Turning behaviour in animals

Comparative analysis of anxiety-like behaviors and sensorimotor functions in two rat mutants, ci2 and ci3, with lateralized rotational behavior

There is increasing evidence that developmental anomalies of cerebral asymmetry are involved in the etiology of psychiatric disorders, including schizophrenia, depression and anxiety. Thus, rodents with abnormal cerebral lateralization are interesting tools to study the association between such anomalies and behavioral dysfunction. The most studied indicator of cerebral asymmetry in the rat is that of circling or rotational behavior. We have recently described two rat mutants, ci2 and ci3, in which lateralized rotational behavior occurs either spontaneously or in response to external stimuli, such as new environment or handling. While cochlear and vestibular defects are found in ci2 rats, ci3 rats do not exhibit any inner ear abnormalities. The abnormal motor response to external stimuli raised the possibility that the circling rat mutants may be more likely to express anxiety-related behavior in tests of emotionality. In the present study, we characterized anxiety-related behaviors of ci2 and ci3 rats in the open field, elevated plus-maze and light/dark exploration test. Furthermore, sensorimotor functions of these rats were evaluated by the rotarod, accelerod and wire hang tests. Heterozygous (ci2/+) littermates or rats of the respective background strains (LEW, BH.7A) were used as controls. In contrast to our expectation, both mutants demonstrated less anxiety-related behavior than controls in tests of emotionality. Ci3 rats exhibited normal sensorimotor functions, whereas marked impairment was observed in ci2 rats, which is most likely a consequence of the vestibular dysfunction in these animals. The acoustic startle response (ASR) and prepulse inhibition of ASR did not differ between ci3 rats and controls. The reduced emotionality of the mutant rats indicated by the present experiments may not be specifically linked to anxiety per se, but is maybe more reflective of impulsivity or the inability to normally perceive or process potentially threatening situations. Based on previous findings of dysfunctions of the central dopamine system in ci2 and ci3 mutant rats, we assume that alterations in dopaminergic activity are involved in the maladaptive behavior observed in the present study.

The chemokine stromal cell-derived factor-1/CXCL12 activates the nigrostriatal dopamine system

We recently demonstrated that dopaminergic (DA) neurons of the rat substantia nigra constitutively expressed CXCR4, receptor for the chemokine stromal cell-derived factor-1 (SDF-1)/CXCL12 (SDF-1). To check the physiological relevance of such anatomical observation, in vitro and in vivo approaches were used. Patch clamp recording of DA neurons in rat substantia nigra slices revealed that SDF-1 (10 nmol/L) induced: (i) a depolarization and increased action potential frequency; and (ii) switched the firing pattern of depolarized DA neurons from a tonic to a burst firing mode. This suggests that SDF-1 could increase DA release from neurons. Consistent with this hypothesis, unilateral intranigral injection of SDF-1 (50 ng) in freely moving rat decreased DA content and increased extracellular concentrations of DA and metabolites in the ipsilateral dorsal striatum, as shown using microdialysis. Furthermore, intranigral SDF-1 injection induced a contralateral circling behavior. These effects of SDF-1 were mediated via CXCR4 as they were abrogated by administration of a selective CXCR4 antagonist. Altogether, these data demonstrate that SDF-1, via CXCR4, activates nigrostriatal DA transmission. They show that the central functions of chemokines are not restricted, as originally thought, to neuroinflammation, but extend to neuromodulatory actions on well-defined neuronal circuits in non-pathological conditions.

Auditory and vestibular defects and behavioral alterations after neonatal administration of streptomycin to Lewis rats: Similarities and differences to the circling (ci2/ci2) Lewis rat mutant

The clinical usefulness of aminoglycoside antibiotics is limited by their ototoxicity. In rodents, damage to the inner ear is often associated with rotational behavior and locomotor hyperactivity reminiscent of such behaviors resulting from an imbalance of forebrain dopamine systems. Based on previous observations in the circling (ci2/ci2) Lewis (LEW) rat mutant, a spontaneous mutation leading to hair cell loss, deafness, impairment of vestibular functions, lateralized circling, hyperactivity and alterations in the nigrostriatal dopamine system, we have recently hypothesized that vestibular defects during postnatal development, independent of whether induced or inherited, lead to secondary changes in the dopaminergic system within the basal ganglia, which would be a likely explanation for the typical behavioral phenotype seen in such models. In the present study, we directly compared the phenotype induced by streptomycin in LEW rats with that of the ci2 LEW rat mutant. For this purpose, we treated neonatal LEW rats over 3 weeks by streptomycin, which induced bilateral degeneration of cochlear and vestibular hair cells. Following this treatment period, the behavioral syndrome of the streptomycin-treated animals, including the lateralized rotational behavior, was almost indistinguishable from that of ci2 mutant rats. However, in contrast to the ci2 mutant rat, all alterations, except the hearing loss, were only transient, disappearing between 7 and 24 weeks following treatment. In conclusion, in line with our hypothesis, vestibular defects induced in normal LEW rats led to the same phenotypic behavior as the inherited vestibular defect of ci2 mutant rats. However, with increasing time for recovery, adaptation to the vestibular impairment developed in streptomycin-treated rats, while all deficits persisted in the mutant animals. At least in part, the transient nature of the abnormal behaviors resulting from treatment with streptomycin could be explained by adaptation to the vestibular impairment by the use of visual cues, which is not possible in ci2 rats because of progressive retinal degeneration in these mutants. Although further experiments are needed to prove this hypothesis, the present study shows that direct comparisons between these two models serve to understand the mechanisms underlying the complex behavioral phenotype in rodents with vestibular defects and how these defects are compensated.

Zolpidem modulates GABA(A) receptor function in subthalamic nucleus

The subthalamic nucleus occupies a position in the indirect pathway of basal ganglia circuit, which plays an important role in the movement regulation. Zolpidem is an imidazopyridine agonist with a high affinity on the benzodiazepine site of GABA(A) receptors containing alpha 1 subunit. Recently, zolpidem has been reported to be useful in treating subgroups of parkinsonian patients. A high density of zolpidem binding sites has been shown in rat subthalamic nucleus. To further investigate the modulation of zolpidem on GABA(A) receptor-mediated inhibitory synaptic current in subthalamic nucleus, whole-cell patch clamp recordings were used in the present study. Zolpidem at 100nM significantly prolonged the decay time and rise time of miniature inhibitory postsynaptic currents, with no effect on the amplitude and frequency. The benzodiazepine antagonist flumazenil could completely block the potentiation induced by zolpidem, confirming the specificity on the benzodiazepine site. At a high concentration of 1 microM, zolpidem significantly increased the decay time, rise time, amplitude and frequency of miniature inhibitory postsynaptic currents. In the behaving rats, unilateral microinjection of zolpidem into subthalamic nucleus induced a significant contralateral rotation. The present findings on the effect of zolpidem in subthalamic nucleus provide a rationale for further investigations into its potential in the treatment of Parkinson's disease.

Alterations in dopamine D3 receptors in the circling (ci3) rat mutant

We have previously described a black-hooded mutant rat (BH.7A/Ztm-ci3/ci3) that displays abnormal lateralized circling behavior, but normal auditory and vestibular functions. Neurochemical determination of dopamine and dopamine metabolite levels in striatum, nucleus accumbens and substantia nigra showed that ci3 rats have a significant asymmetry in striatal dopamine in that dopamine levels were significantly lower in the hemisphere contralateral to the preferred direction of turning. Consistent with this finding, immunohistological examination of dopaminergic neurons in substantia nigra and ventral tegmental area yielded a significant laterality in the medial part of substantia nigra pars compacta with a lower density of tyrosine hydroxylase-positive neurons in the contralateral hemisphere of mutant circling rats, while no laterality was seen in unaffected rats of the background strain. In the present study, quantitative autoradiography was used to examine the binding of [(3)H]SCH 23390, [(3)H]raclopride and [(3)H]7-OH-DPAT (7-hydroxy-N,N-di-n-propyl-2-aminotetralin) to dopamine D1, D2, and D3 receptors, respectively, in various brain regions of ci3 rats and unaffected rats of the background strain (BH.7A(LEW)/Won). No significant differences between circling rats and controls were obtained for D1 and D2 receptor binding in any region, but mutant rats differed from controls in dopamine D3 binding in several regions. A significant decrease in D3 binding was seen in the shell of the nucleus accumbens, the islands of Calleja, and the subependymal zone of ci3 mutant rats. Furthermore, a significant laterality in D3 binding was determined in ci3 rats in that binding was lower in the contralateral hemisphere in the shell of the nucleus accumbens and the islands of Calleja. Our data indicate that alterations of dopamine D3 receptors may be involved in the behavioral phenotype of the ci3 rat, thus substantiating the findings from a recent genetic linkage analysis that indicated the D3 receptor gene as a candidate gene in this rat mutant.

Substantia nigra osmoregulation: taurine and ATP involvement

An extracellular nonsynaptic taurine pool of glial origin was recently reported in the substantia nigra (SN). There is previous evidence showing taurine as an inhibitory neurotransmitter in the SN, but the physiological role of this nonsynaptic pool of taurine has not been explored. By using microdialysis methods, we studied the action of local osmolarity on the nonsynaptic taurine pool in the SN of the rat. Hypoosmolar pulses (285-80 mosM) administered in the SN by the microdialysis probe increased extrasynaptic taurine in a dose-dependent way, a response that was counteracted by compensating osmolarity with choline. The opposite effect (taurine decrease) was observed when osmolarity was increased. Under basal conditions, the blockade of either the AMPA-kainate glutamate receptors with 6-cyano-7-nitroquinoxaline-2,3-dionine disodium or the purinergic receptors with pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid modified the taurine concentration, suggesting that both receptors modulate the extrasynaptic pool of taurine. In addition, these drugs decreased the taurine response to hypoosmolar pulses, suggesting roles for glutamatergic and purinergic receptors in the taurine response to osmolarity. The participation of purinergic receptors was also supported by the fact that ATP (which, under basal conditions, increased the extrasynaptic taurine in a dose-dependent way) administered in doses saturating purinergic receptors also decreased the taurine response to hypoosmolarity. Taken together, present data suggest osmoregulation as a role of the nonsynaptic taurine pool of the SN, a function that also involves glutamate and ATP and that could influence the nigral cell vulnerability in Parkinson's disease.

Quantitative measurement of neurological deficit after mild (30 min) transient middle cerebral artery occlusion in rats

Although 30-min transient middle cerebral artery occlusion (30-min tMCAo) causes reproducible subcortical infarction in rats, it is difficult to evaluate the resulting neurological deficit using common behavioral tests such as the rota-rod test, adhesive-removal test, or narrow beam test. Establishment of a method of quantitative evaluation would help to develop a novel therapeutic approach to treat cerebral infarction. To solve this problem, we examined whether the neurological deficit could be detected by the Montoya staircase test or methamphetamine-induced rotation, which are commonly used in a Parkinson disease model induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA). From 10 to 14 days after tMCAo, the Montoya staircase test showed significant clumsiness in forelimb tasks contralateral to the lesion side, whereas sham-operated rats showed no significant clumsiness in both forelimbs. The number of ipsilateral rotations induced by methamphetamine was also increased in tMCAo-rats at 21 days after tMCAo. Although Pearson's correlations coefficient showed that the results of these tests were correlated with the infarction volume, there was no significant correlation between the results of these two tests. These findings imply that the neurological deficit detected by both tests might reflect the severity of ischemic injury, but each test might evaluate different aspects of neurological deficit. Thus, the Montoya staircase test and methamphetamine-induced rotation are useful to evaluate neurological deficit in the chronic stage of subcortical infarction induced by 30-min tMCAo.

Oncoprotein Akt/PKB induces trophic effects in murine models of Parkinson's disease

Despite promising preclinical studies, neurotrophic factors have not yet achieved an established role in the treatment of human neurodegenerative diseases. One impediment has been the difficulty in providing these macromolecules in sufficient quantity and duration at affected sites. An alternative approach is to directly activate, by viral vector transduction, intracellular signaling pathways that mediate neurotrophic effects. We have evaluated this approach in dopamine neurons of the substantia nigra, neurons affected in Parkinson's disease, by adeno-associated virus 1 transduction with a gene encoding a myristoylated, constitutively active form of the oncoprotein Akt/PKB. Adeno-associated virus Myr-Akt has pronounced trophic effects on dopamine neurons of adult and aged mice, including increases in neuron size, phenotypic markers, and sprouting. Transduction confers almost complete protection against apoptotic cell death in a highly destructive neurotoxin model. Activation of intracellular neurotrophic signaling pathways by vector transfer is a feasible approach to neuroprotection and restorative treatment of neurodegenerative disease.

Relation between rotation in the 6-OHDA lesioned rat and dopamine loss in striatal and substantia nigra subregions

The relation between the rotation response to drug-induced activation of the dopamine (DA) receptor in the rat unilaterally lesioned with 6-hydroxydopamine (6-OHDA) in the substantia nigra (SN) and the loss of DA in subregions of the SN and caudate-putamen (C/PUT) is not clear. Here this relation was examined in 23 rats classified as rotators to amphetamine (5 mg/kg). After their response was characterized in terms of ipsilateral rotation, contralateral rotation, and oral stereotypy in one place, they were divided into high, medium, low, and very low rotators. The loss of DA in each group was visualized on brain sections immunoreacted to tyrosine hydroxylase (TH). The density of the TH label on the side of the lesion was compared to that on the intact side. In the ventral midbrain, the density was determined in the SN subdivided into far lateral, lateral, central, and medial subregions and also in the ventral tegmental area (VTA). In the forebrain, it was determined in the C/PUT subdivided into lateral, central, and medial subregions and also in the nucleus accumbens (ACC). These measurements led to three principal findings. The first was a positive overall correlation between rotation and loss of TH label. The second was a correlation between rotation and penetration of the loss from the lateral subregions into more medial areas. The third was a larger loss in SN and VTA (midbrain) than in C/PUT and ACC (forebrain). These findings show that rotation depended not only on the overall loss of DA but also on its distribution across subregions. The loss in the lateral subregion, always the largest regardless of the rate of rotation, may have been the first step in inducing the motor abnormality, and the loss in the central and medial subregions may have served to enhance the abnormality due to the loss in the lateral subregion.

Glycine release in the substantia nigra: Interaction with glutamate and GABA

Previous studies have reported a high number of glycine (GLY) receptors in the substantia nigra (SN) but a low number of GLY-neurons, suggesting that taurine, a partial agonist of GLY-receptors, is the natural substrate for SN GLY-receptors. By using microdialysis to quantify amino acids in the extracellular space of the SN, we observed an extracellular pool of GLY in the rat that increased after depolarizing with high-K+ in a Ca2+-dependent manner and that diffuses through the extracellular space. GLY markedly increased after blocking either the tricarboxylic cycle with fluorocitrate or the glutamine synthetase activity with MSO. Because these products act selectively on glial cells, their effects show glia as a key cell in maintaining the extracellular pool of GLY in the SN. Extracellular GLY was modified by glutamate and glutamate receptor agonists. The local administration of GLY modified the extracellular concentration of GABA. Taken together, the complex regulation of the extracellular level of GLY, its possible glial origin and interaction with glutamate and GABA suggest a volume transmitter role for GLY in the SN, a possibility which also agrees with the recent finding of GLY-transporters in this centre.

Impairment of skilled forelimb use after ablation of striatal interneurons expressing substance P receptors in rats: an analysis using a pasta matrix reaching task

Local injection of substance P (SP)-saporin can cause selective ablation of striatal interneurons expressing SP receptors (SPR). In this study, we evaluated quantitatively the impairment of skilled forelimb use after unilateral ablation of the striatal interneurons using a pasta matrix reaching task in rats. We found a significant decrease of the number of the pasta pieces (uncooked spaghetti) retrieved using the paw of the experimental side contralateral to the ablation, whereas the number of the pasta pieces retrieved using the paw of the intact side increased significantly. These findings, with our previous reports, suggest that the modulation of the cortico-striato-entopeduncular direct pathway by striatal interneurons is important for maintaining normal basal-ganglia control for skilled forelimb movements.

Role of nitric oxide on motor behavior

The present review paper describes results indicating the influence of nitric oxide (NO) on motor control. Our last studies showed that systemic injections of low doses of inhibitors of NO synthase (NOS), the enzyme responsible for NO formation, induce anxiolytic effects in the elevated plus maze whereas higher doses decrease maze exploration. Also, NOS inhibitors decrease locomotion and rearing in an open field arena. These results may involve motor effects of this compounds, since inhibitors of NOS, NG-nitro-L-arginine (L-NOARG), N(G)-nitro-L-arginine methylester (L-NAME), N(G)-monomethyl-L-arginine (L-NMMA), and 7-Nitroindazole (7-NIO), induced catalepsy in mice. This effect was also found in rats after systemic, intracebroventricular or intrastriatal administration. Acute administration of L-NOARG has an additive cataleptic effect with haloperidol, a dopamine D2 antagonist. The catalepsy is also potentiated by WAY 100135 (5-HT1a receptor antagonist), ketanserin (5HT2a and alfal adrenergic receptor antagonist), and ritanserin (5-HT2a and 5HT2c receptor antagonist). Atropine sulfate and biperiden, antimuscarinic drugs, block L-NOARG-induced catalepsy in mice. L-NOARG subchronic administration in mice induces rapid tolerance (3 days) to its cataleptic effects. It also produces cross-tolerance to haloperidol-induced catalepsy. After subchronic L-NOARG treatment there is an increase in the density NADPH-d positive neurons in the dorsal part of nucleus caudate-putamen, nucleus accumbens, and tegmental pedunculupontinus nucleus. In contrast, this treatment decreases NADPH-d neuronal number in the substantia nigra compacta. Considering these results we suggest that (i) NO may modulate motor behavior, probably by interfering with dopaminergic, serotonergic, and cholinergic neurotransmission in the striatum; (ii) Subchronic NO synthesis inhibition induces plastic changes in NO-producing neurons in brain areas related to motor control and causes cross-tolerance to the cataleptic effect of haloperidol, raising the possibility that such treatments could decrease motor side effects associated with antipsychotic medications. Finally, recent studies using experimental Parkinson's disease models suggest an interaction between NO system and neurodegenerative processes in the nigrostriatal pathway. It provides evidence of a protective role of NO. Together, our results indicate that NO may be a key participant on physiological and pathophysiological processes in the nigrostriatal system.

Behavioral and anatomical effects of quinolinic acid in the striatum of the hemiparkinsonian rat

Parkinson's disease (PD), a hypokinetic disorder, and Huntington's disease (HD), a hyperkinetic disorder, share the fact that in the motor pathways the dysfunction starts in the striatum. In PD the projection neurons are overactive due to decreased inhibitory regulation by lost dopamine afferents, while in HD the output from the striatum is insufficient due to loss of projection neurons. This study aimed to determine whether the introduction of a mild HD condition in the PD striatum can counter the hypokinetic condition. The experiment was carried out in the 6-OHDA rat model for PD in which amphetamine, 5 mg/kg, evokes an asymmetric rotation response toward the side of the 6-OHDA lesion (ipsilateral rotation). The response to amphetamine in this study was fractionated into multiple components and measured automatically. After baseline measurements, the subjects were divided into four groups. Group I was unilaterally sham-lesioned in medial, central, and lateral striatum. Group II was injected quinolinic acid (QA) 20 nM in medial, central, and lateral striatum. Group III was injected QA 60 nM in central striatum. Group IV was injected QA 120 nM in central striatum. The effects of QA were measured weekly. The sham lesions in Group I had no effects. In Group II, ipsilateral rotation was reduced and replaced by oral stereotypy, a competitive behavior. In Group III, ipsilateral rotation decreased, but to a lesser degree than in Group II. In Group IV, QA had no effects. Histological findings show a unilateral loss of tyrosine immunoreactive (TH) neurons in substantia nigra and of fibers in striatum in all subjects. In addition, in Group II the striatum was atrophied. These findings suggest that the shift in Group II from ipsilateral rotation to oral stereotypy after QA was due to reduced striatal output caused by a loss of projection neurons, a loss insufficient to induce HD symptoms, but sufficient to counter the PD condition.

Serotonergic influence on the potentiation of D-amphetamine and apomorphine-induced rotational behavior by the α2-adrenoceptor antagonist 2-methoxy idazoxan in hemiparkinsonian rats

The alpha(2)-adrenoceptor antagonists potentiate both ipsilateral and contralateral rotations induced by amphetamine and apomorphine respectively in hemiparkinsonian rats. The present study investigated the role of serotonergic transmission in this potentiation in unilaterally 6-hydroxydopamine nigral lesioned rats. D-amphetamine (0.5 mg/kg, i.p.) produced ipsilateral rotations, which were decreased by the dopamine receptor antagonist haloperidol (0.2 mg/kg, i.p.) and the alpha(1)-receptor antagonist prazosin (1 mg/kg, i.p.). The selective alpha(2)-antagonist 2-methoxy idazoxan (0.2 mg/kg, i.p.) potentiated the amphetamine-induced ipsilateral rotations, that were attenuated by haloperidol and prazosin. The selective serotonin re-uptake inhibitor citalopram (10 mg/kg, i.p.) and selective serotonin synthesis inhibitor p-chlorophenylalanine (150 mg/kg, i.p., 3 days) decreased and increased the observed potentiation respectively. Apomorphine (0.2 mg/kg, s.c.) produced contralateral rotations, which were decreased by haloperidol but not by prazosin. 2-methoxy idazoxan potentiated these rotations which were attenuated by haloperidol but not by prazosin. Citalopram and p-chlorophenylalanine increased and decreased the observed potentiation respectively. Citalopram and p-chlorophenylalanine had no effect by per se on D-amphetamine and apomorphine-induced rotations. 2-methoxy idazoxan alone increased both ipsilateral and contralateral spontaneous rotations. Taken together, these findings indicate that an increase in noradrenergic tone by 2-methoxy idazoxan potentiates both D-amphetamine-induced ipsilateral and apomorphine induced contralateral rotations. alpha(1)-Antagonism attenuates D-amphetamine induced ipsilateral rotations and its potentiation by 2-methoxy idazoxan but not apomorphine rotations or its potentiation. Increasing and decreasing the serotonergic transmission decreases and increases D-amphetamine potentiation, whereas increases and decreases apomorphine potentiation respectively. The possible mechanisms for these findings are discussed.

Locomotor effects of imidazoline I2-site-specific ligands and monoamine oxidase inhibitors in rats with a unilateral 6-hydroxydopamine lesion of the nigrostriatal pathway

The present study examined the ability of the selective imidazoline I(2)-site ligands 2-(-2-benzofuranyl)-2-imidazoline (2-BFI) and 2-[4,5-dihydroimidaz-2-yl]-quinoline (BU224) and selected monoamine oxidase (MAO) inhibitors to evoke locomotor activity in rats bearing a lesion of the nigrostriatal pathway. Male Sprague-Dawley rats were injected with 12.5 microg 6-hydroxydopamine (6-OHDA) into the right median forebrain bundle to induce a unilateral lesion of the nigrostriatal tract. After 6 weeks, test drugs were administered either alone or in combination with L-DOPA (l-3,4-dihydroxyphenylamine) and the circling behaviour of animals was monitored as an index of anti-Parkinsonian activity. Intraperitoneal (i.p.) administration of the irreversible MAO-B inhibitor deprenyl (20 mg kg(-1)) or the imidazoline I(2)-site ligands BU224 (14 mg kg(-1)) and 2-BFI (7 and 14 mg kg(-1)) produced significant increases in ipsiversive rotations compared to vehicle controls totaling, at the highest respective doses tested, 521 +/-120, 131 +/- 37 and 92.5 +/- 16.3 net contraversive rotations in 30 (deprenyl) or 60 (BU224 and 2-BFI) min. In contrast, the reversible MAO-A inhibitor moclobemide (2.5-10 mg kg(-1)) and the reversible MAO-B inhibitor lazabemide (2.5-10 mg kg(-1)) failed to instigate significant rotational behaviour compared to vehicle. Coadministration of lazabemide (10 mg kg(-1)), moclobemide (10 mg kg(-1)) or 2-BFI (14 mg kg(-1)) with L-DOPA (20 mg kg(-1)) significantly increased either the duration or total number of contraversive rotations emitted over the testing period in comparison to L-DOPA alone. These data suggest that I(2)-specific ligands have dual effects in the 6-OHDA-lesioned rat model of Parkinson's disease; a first effect associated with an increase in activity in the intact hemisphere, probably via an increase in striatal dopamine content, and a secondary action which, through the previously documented inhibition of MAO-A and/or MAO-B, increases the availability of dopamine produced by L-DOPA.

High-frequency stimulation of the subthalamic nucleus reverses limb-use asymmetry in rats with unilateral 6-hydroxydopamine lesions

Deep brain stimulation (DBS) is a widely used clinical treatment for Parkinson's disease (PD). A rodent model of DBS is a necessary tool for understanding the neural mechanisms of this method. Our previous study showed that high-frequency stimulation (HFS) of the subthalamic nucleus (STN) improved treadmill locomotion in rats with unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of nigrostriatal dopamine (DA) neurons. The present study tested DBS effects on limb-use asymmetry (LUA) during vertical/lateral exploration in a cylindrical chamber in rats with similar unilateral nigrostriatal DA lesions. Limb-use asymmetry assessment has been used to detect functional capacity over a wide range of dopamine depletion. Before lesioning, rats exhibited regular rearing activity and used both forelimbs equally often to support weight during exploration of the walls of the cylinder. After unilateral nigrostriatal DA lesioning, rats displayed reduced rearing activity and predominant use of the ipsilateral (good) forelimb to touch the wall. HFS of the STN, but not of other nearby regions surrounding the STN, in the lesioned rats restored normal rearing activity and reversed the limb-use asymmetry caused by the unilateral DA depletion. This study is consistent with the possibility that there can be beneficial effects of STN-DBS on behavioral impairments in unilateral DA-depleted rats and may suggest an appropriate rodent model for DBS study.

Noradrenergic mechanisms in neurodegenerative diseases: a theory

A deficiency in the noradrenergic system of the brain, originating largely from cells in the locus coeruleus (LC), is theorized to play a critical role in the progression of a family of neurodegenerative disorders that includes Parkinson's disease (PD) and Alzheimer's disease (AD). Consideration is given here to evidence that several neurodegenerative diseases and syndromes share common elements, including profound LC cell loss, and may in fact be different manifestations of a common pathophysiological process. Findings in animal models of PD indicate that the modification of LC-noradrenergic activity alters electrophysiological, neurochemical and behavioral indices of neurotransmission in the nigrostriatal dopaminergic system, and influences the response of this system to experimental lesions. In models related to AD, noradrenergic mechanisms appear to play important roles in modulating the activity of the basalocortical cholinergic system and its response to injury, and to modify cognitive functions including memory and attention. Mechanisms by which noradrenaline may protect or promote recovery from neural damage are reviewed, including effects on neuroplasticity, neurotrophic factors, neurogenesis, inflammation, cellular energy metabolism and excitotoxicity, and oxidative stress. Based on evidence for facilitatory effects on transmitter release, motor function, memory, neuroprotection and recovery of function after brain injury, a rationale for the potential of noradrenergic-based approaches, specifically alpha2-adrenoceptor antagonists, in the treatment of central neurodegenerative diseases is presented.

Subthalamic high frequency stimulation induced rotations are differentially mediated by D1 and D2 receptors

High frequency stimulation (HFS) of the subthalamic nucleus (STN) has clinically emerged as a promising approach in the treatment of Parkinson's disease, epilepsy, dystonia as well as compulsive and possibly other mood disorders. The underlying mechanisms are incompletely understood, but are definitely related to high frequency and likely to involve the dopamine (DA)-system. To further test this hypothesis the present study investigated the modulation of STN-HFS-induced circling by systemic and intracerebral injection of drugs acting on DA receptors in naive freely moving rats. Within this experimental setup, unilateral STN-HFS alone induced intensity-dependent circling. Systemic injections of selective D1- (SCH-23390) and D2-((-)-sulpiride) antagonists as well as the mixed D1 and D2 agonist apomorphine dose-dependently reduced STN-HFS-induced rotational behavior. Intracerebral microinjections of (-)-sulpiride but not SCH-23390 decreased circling when injected intrastriatally and increased the number of rotations when injected intranigrally (pars reticulata (SNr)). These data reveal that STN-HFS-induced contralateral circling is differentially modulated by D1 and D2 receptors. While D2 receptor-mediated effects involve the dorso-/ventrolateral striatum and the SNr, D1 receptors probably exert their actions via brain areas outside the striatum and SNr. These findings suggest the nigrostriatal DA-system to be specifically involved in the mediation of STN-HFS-induced motor effects.

Extracellular taurine in the substantia nigra: Taurine-glutamate interaction

Taurine has been proposed as an inhibitory transmitter in the substantia nigra (SN), but the mechanisms involved in its release and uptake remain practically unexplored. We studied the extracellular pool of taurine in the rat's SN by using microdialysis methods, paying particular attention to the taurine-glutamate (GLU) interaction. Extracellular taurine increased after cell depolarization with high-K(+) in a Ca(2+)-dependent manner, being modified by the local perfusion of GLU, GLU receptor agonists, and zinc. Nigral administration of taurine increased the extracellular concentration of gamma-aminobutyric acid (GABA) and GLU, the transmitters of the two main inputs of the SN. The modification of the glial metabolism with fluocitrate and L-methionine sulfoximine also changed the extracellular concentration of taurine. The complex regulation of the extracellular pool of taurine, its interaction with GABA and GLU, and the involvement of glial cells in its regulation suggest a volume transmission role for taurine in the SN.

Effects of electrolytic and 6-hydroxydopamine lesions of rat nigrostriatal pathway on nitric oxide synthase and nicotinamide adenine dinucleotide phosphate diaphorase

The aim of the present study was to assess degenerative changes in the nitric oxide (NO) system of basal ganglia in animals with experimentally induced Parkinson's disease. In one procedure, rats were stereotaxically injected with 6-hydroxydopamine (6-OHDA) in the right medial forebrain bundle; in a second procedure, electrodes were implanted in the right substantia nigra pars compacta (SNc). After 15 and 30 days animals were tested for rotational asymmetry induced by apomorphine. Apomorphine induced rotation in lesioned animals, towards the ipsilateral side after electrolytic lesion and towards contralateral side in 6-OHDA animals. Structural deficits in basal ganglia were quantified by nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and by nitric oxide synthase (NOS) immunoreactivity. 6-OHDA and electrolytic lesions induced a significant decrease in the number of NADPH-d/NOS positive cells in the lesion ipsilateral to SNc, in contrast with cell number increase in the ipsilateral dorsal striatum. By contrast, 6-OHDA-treated animals showed a decrease in the number of NOS immunoreactive cells in the contralateral nucleus accumbens. We conclude that populations of NO-synthesizing neurons are differentially regulated in Parkinson's disease induced by different experimental procedures.

Turning behaviour induced by stimulation of the 5-HT receptors in the subthalamic nucleus

The basal ganglia, which receive a rich serotonergic innervation, have been implicated in hyperkinetic and hypokinetic disorders. Moreover, a decrease in subthalamic nucleus (STN) activity has been associated with motor hyperactivity. To address the role of subthalamic serotonergic innervation in its motor function, turning behaviour was studied in rats with stimulation of the subthalamic serotonin (5-HT) receptors by intracerebral microinjections. The intrasubthalamic administration of 5-HT induced dose-dependent contralateral turning behaviour, with a maximal effect at a dose of 2.5 microg in 0.2 microL. Similar results were observed with microinjections of other 5-HT receptor agonists: quipazine (a 5-HT2B/C/3 agonist), MK-212 (a 5-HT2B/C agonist) and m-chlorophenylbiguanidine (a 5-HT3 agonist), while microinjections of 5-HT into the zona incerta or in the previously lesioned STN were ineffective. The effect of 5-HT was blocked by coadministration of the antagonist mianserin. Stimulation of subthalamic 5-HT receptors in animals bearing a lesion of the nigrostriatal pathway did not modify the motor response, which indicates that the dopamine innervation of the nucleus is not involved in this effect. Kainic acid lesion of the substantia nigra pars reticulata (SNr) suppressed the contralateral rotations elicited by stimulation of 5-HT2B/C/3 subthalamic receptors. This suggests a role of the subthalamic-nigral pathway in the turning activity. Furthermore, the partial blockade of glutamatergic receptors in the SNr by the antagonist DNQX increased the contralateral circling elicited by stimulation of 5-HT receptors in the STN. We concluded that the activation of the 5-HT2B/C and 5-HT3 subthalamic receptors elicited contralateral turning behaviour, probably via the subthalamic-nigral pathway.

The effects of chronic L-DOPA therapy on pharmacodynamic parameters in a rat model of motor response fluctuations

Chronic L-3,4-dihydroxyphenylalanine (L-DOPA) therapy in Parkinson's disease (PD) is complicated by motor response fluctuations and dyskinesia. The relative contributions of disease severity and chronic L-DOPA therapy to the development of motor fluctuation are not well defined clinically. Experimental studies have been limited partly because models for the antiparkinsonian effects on akinesia have not been employed. Therefore, we employed a model of akinesia using forepaw adjusting steps that have been well characterized to reflect the effect of lesions and the antiparkinsonian effect of dopaminergic drugs and transplants. We administered L-DOPA (12.5 mg/kg) intermittently for 4 weeks to rats with severe nigrostriatal lesions produced by injecting 6-hydroxydopamine into the medial forebrain bundle. The peak magnitude responses to L-DOPA increased after treatment compared to the pretreatment baseline. The latency to peak response to L-DOPA became shorter and reversed after the discontinuation of treatment. The duration of response showed minor changes. The pattern of changes in response to apomorphine was similar to that of L-DOPA except that the peak magnitude did not increase despite chronic L-DOPA treatment. The changes in D1 and D2 receptor binding did not correlate with behavioral changes. In summary, long-term intermittent L-DOPA treatment resulted in priming of antiparkinsonian effects on improving akinesia in a rat model of severe PD. These observed changes do not mirror all aspects of motor response fluctuations in advanced PD patients and suggest differential contributions of dopaminergic treatment and lesion severity to motor complication patterns.

Conditional ablation of striatal neuronal types containing dopamine D2 receptor disturbs coordination of basal ganglia function

Dopamine (DA) exerts synaptic organization of basal ganglia circuitry through a variety of neuronal populations in the striatum. We performed conditional ablation of striatal neuronal types containing DA D2 receptor (D2R) by using immunotoxin-mediated cell targeting. Mutant mice were generated that express the human interleukin-2 receptor alpha-subunit under the control of the D2R gene. Intrastriatal immunotoxin treatment of the mutants eliminated the majority of the striatopallidal medium spiny neurons and cholinergic interneurons. The elimination of these neurons caused hyperactivity of spontaneous movement and reduced motor activation in response to DA stimulation. The elimination also induced upregulation of GAD gene expression in the globus pallidus (GP) and downregulation of cytochrome oxidase activity in the subthalamic nucleus (STN), whereas it attenuated DA-induced expression of the immediate-early genes (IEGs) in the striatonigral neurons. In addition, chemical lesion of cholinergic interneurons did not alter spontaneous movement but caused a moderate enhancement in DA-induced motor activation. This enhancement of the behavior was accompanied by an increase in the IEG expression in the striatonigral neurons. These data suggest that ablation of the striatopallidal neurons causes spontaneous hyperactivity through modulation of the GP and STN activity and that the ablation leads to the reduction in DA-induced behavior at least partly through attenuation of the striatonigral activity as opposed to the influence of cholinergic cell lesion. We propose a possible model in which the striatopallidal neurons dually regulate motor behavior dependent on the state of DA transmission through coordination of the basal ganglia circuitry.

Timecourse of striatal re-innervation following lesions of dopaminergic SNpc neurons of the rat

Previously we described the extent of sprouting that axons of the rat substantia nigra pars compacta (SNpc) undergo to grow new synapses and re-innervate the dorsal striatum 16 weeks after partial lesions. Here we provide insights into the timing of events related to the re-innervation of the dorsal striatum by regenerating dopaminergic nigrostriatal axons over a 104-week period after partial SNpc lesioning. Density of dopamine transporter and tyrosine hydroxylase immunoreactive axonal varicosities (terminals) decreased up to 80% 4 weeks after lesioning but returned to normal by 16 weeks, unless SNpc lesions were greater than 75%. Neuronal tracer injections into the SNpc revealed a 119% increase in axon fibres (4 mm rostral to the SNpc) along the medial forebrain bundle 4 weeks after lesioning. SNpc cells underwent phenotypic changes. Four weeks after lesioning the proportion of SNpc neurons that expressed tyrosine hydroxylase fell from 90% to 38% but returned to 78% by 32 weeks. We discuss these phenotype changes in the context of neurogenesis. Significant reductions in dopamine levels in rats with medium (30-75%) lesions returned to normal by 16 weeks whereas recovery was not observed if lesions were larger than 75%. Finally, rotational behaviour of animals in response to amphetamine was examined. The clear rightward turning bias observed after 2 weeks recovered by 16 weeks in animals with medium (30-75%) lesions but was still present when lesions were larger. These studies provide insights into the processes that regulate sprouting responses in the central nervous system following injury.

Changes in function and ultrastructure of striatal dopaminergic terminals that regenerate following partial lesions of the SNpc

Following partial substantia nigra lesions, remaining dopaminergic neurones sprout, returning terminal density in the dorsal striatum to normal by 16 weeks. This suggests regeneration and maintenance of terminal density is regulated to release appropriate levels of dopamine. This study examined the structure and function of these reinnervated terminals, defining characteristics of dopamine uptake and release, density and affinity of the dopamine transporter (DAT) and ultrastructural morphology of dopamine terminals in the reinnervated dorsal striatum. Finally, rotational behaviour of animals in response to amphetamine was examined 4 and 16 weeks after substantia nigra pars compacta (SNpc) lesions. Dopamine transport was markedly reduced 16 weeks after lesioning along with reduced density and affinity of DAT. Rate of dopamine release and peak concentration, measured electrochemically, was similar in lesioned and control animals, while clearance was prolonged after lesioning. Ultrastructurally, terminals after lesioning were morphologically distinct, having increased bouton size, vesicle number and mitochondria, and more proximal contacts on post-synaptic cells. After 4 weeks, tendency to rotate in response to amphetamine was proportional to lesion size. By 16 weeks, rotational behaviour returned to near normal in animals where lesions were less than 70%, although some animals demonstrated unusual rotational patterns at the beginning and end of the amphetamine effect. Together, these changes indicate that sprouted terminals are well compensated for dopamine release but that transport mechanisms are functionally impaired. We discuss these results in terms of implications for dyskinesia and other behavioural states.

Behavioral/neurophysiological investigation of effects of combining a quinolinic acid entopeduncular lesion with a fetal mesencephalic tissue transplant in striatum of the 6-OHDA hemilesioned rat

Behavioral and electrophysiological methods were used to investigate the effects of combining a unilateral quinolinic acid lesion of the entopeduncular nucleus (QA/EP) with a striatal transplant of fetal ventral mesencephalic tissue in the 6-hydroxydopamine (6-OHDA) hemilesioned rat model for Parkinson's disease. The subjects were 6-OHDA-lesioned rats selected because their response to amphetamine treatment was a strongly biased rotation toward the side of the 6-OHDA lesion in the substantia nigra, at the expense of other evoked behaviors associated with amphetamine. Two experiments were performed. In the first, the motor effects of the QA/EP lesion alone and of the combination of QA/EP lesion with striatal transplant were determined by measuring six aspects of the motor response. In the second the electrophysiological effects of the two interventions on the responses of neurons in the subthalamic nucleus to amphetamine and apomorphine were determined in the 6-OHDA-lesioned rats. The results of the first experiment show that the QA/EP lesion by itself produced an attenuation of the rotation response and, simultaneously, an increase of oral stereotypy. They also show that the combination of QA/EP lesion with striatal transplant was more effective than the single intervention, inducing more attenuation of rotation and more oral stereotypy. The results of the second experiment show that the responses of subthalamic neurons to amphetamine in the behaving hemiparkinsonian rat with combined QA/EP lesion and transplant were larger than the responses in the hemiparkinsonian rat with the QA/EP lesion alone. However, even these larger responses in the rats with combined intervention were not as large as those recorded at the same time in the subthalamus in the opposite, intact, hemisphere. The results of the two experiments, both of which show enhanced motor and neuronal sensitivity to amphetamine after the combined intervention, suggest that such a multiple approach might prove more beneficial than a one-site intervention targeting either the EP or the striatum.

Behavioral and subthalamic effects of combining a fetal ventral mesencephalic transplant in striatum with an electrolytic lesion of the entopeduncular nucleus in the rat with a unilateral 6-OHDA lesion of substantia nigra

Behavioral and electrophysiological methods were used to determine whether a transplant of dopamine-rich fetal tissue in striatum combined with an electrolytic lesion of the entopeduncular nucleus have additive effects in the unilaterally lesioned rat model for Parkinson's disease. The subjects were rats with the left substantia nigra lesioned with 6-hydroxydopamine (6-OHDA) and responding to systemic amphetamine with rotation toward the side of the lesion (ipsilateral rotation). The motor response to amphetamine was fractionated into six aspects, half reflecting the unilateral deafferentation in striatum and half representing those aspects of the response evoked in normal rats. After collection of baseline values, 25 rotators received a transplant of fetal ventral mesencephalic tissue in the left striatum and 20 received a transplant and, at the same time, an electrolytic lesion of the left entopeduncular nucleus. Testing for the motor response to amphetamine resumed after 4 weeks of recovery and continued at weekly intervals for 5 weeks. Upon completion of these tests, each rotator was implanted with multiple electrodes in the subthalamic nucleus. After recovery, multiunit responses to amphetamine and apomorphine were recorded from several electrodes in parallel during the motor response to the drugs. In rotators with transplant only, treatment with amphetamine evoked oral stereotypy and an attenuated ipsilateral rotation response. In rotators with combined transplant and entopeduncular lesion, ipsilateral rotation did not change or increased. Subthalamic responses to amphetamine and apomorphine were larger in rotators with combined transplant and entopeduncular lesion than in rotators with transplant alone. These findings indicate that the combination of transplant and pallidotomy in the 6-OHDA rat model for parkinsonism does not lead to additive benefits, an effect that may have been due to the nonselectivity of the electrolytic damage and/or of the lesion extending beyond the entopeduncular nucleus into the lateral hypothalamus.

Host brain regulation of dopaminergic grafts function: role of the serotonergic and noradrenergic systems in amphetamine-induced responses

The indirect dopaminergic (DA) agonist amphetamine has frequently been used to study functional responses of DA grafted neurons. However, it is not known if striatal responses, primarily related to DA release by the grafted neurons, are modulated by the host striatal afferents. We investigated the changes in amphetamine-induced rotational behavior and striatal expression of Fos in DA-denervated and grafted rats subjected to serotonergic denervation and/or treatment with the alpha(1)-adrenergic receptor antagonist Prazosin. Acute serotonergic lesions with p-chlorophenylalanine suppressed the expression of Fos induced by 1 mg/kg of amphetamine in both the grafted and the contralateral striatum. Chronic serotonergic denervation with 5,7-dihydroxytryptamine induced a significant reduction in Fos expression in both the grafted and nongrafted striata and a nonsignificant reduction in the contraversive rotation. In DA-innervated striata, Prazosin significantly reduced the expression of Fos but only in the presence of serotonergic innervation. However, Prazosin did not decrease the expression of Fos induced by grafts located in striata not subjected to serotonergic denervation. The present results suggest functional integration of transplanted DA neurons and major host striatal afferent systems, particularly the serotonergic system, in modulating responses of the host striatal neurons. However, indirect effects exerted by the noradrenergic system on the normal striatum were not observed in the DA-denervated and grafted striata.

Asymmetrical development of the monoamine systems in 2,4-dichlorophenoxyacetic acid treated rats

The purpose of this study was to determine whether the regional brain biogenic amine levels in adult rats were altered by pre- and post-natal exposure to 2,4-dichlorophenoxyacetic acid (2,4-D). Pregnant rats were daily orally exposed to 70 mg/kg per day of 2,4-D from gestation day (GD) 16 to post-partum day (PPD) 23. After weaning, the pups were assigned to one of two subgroups: T1 fed with untreated diet up to post-natal day (PND) 90 and T2 (maintained with 2,4-D diet up to PND 90). In addition, we wanted to know the effect of 2,4-D on lateralization in the monoamine systems of the basal ganglia of these adult rats and whether there was any correlation with the behavioral developmental pattern previously reported by us. In this study the content of noradrenaline (NA) was significantly increased in substantia nigra (SN) while it decreased in cerebellum in male and female rats of T2 group. The decreased dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovallinic acid (HVA) contents in cerebellum, midbrain, ventral tegmental area (VTA) and prefrontal cortex (PFc) showed an alteration in the mesocorticolimbic system. However, an increase of DA in SN and of DOPAC and HVA in nucleus accumbens (NAc) in both sexes and of DA and DOPAC (only in females) in striatum was detected. The contents of serotonin (5-hydroxytryptamine, 5-HT) were significantly increased in both sexes in PFc, striatum (St), midbrain, SN and cerebellum. Variations of any monoamine levels in NAc and VTA were determined. T1 rats were irreversibly altered: a diminution in DA and/or DOPAC levels in PFc, midbrain, VTA and cerebellum was determined. Indolamines of these rats were increased in both sexes in PFc and St. There was also a large increase in 5-HT levels in midbrain of male rats. Although no changes in the dopaminergic system with respect to their control values in any side of these brain structures were observed, DA and DOPAC levels were found to be decreased in the right side with respect to the left side in striata and accumbens nuclei in T2 female rats supporting the behavioral rotation previously registered by us in these rats. In addition, the increased 5-HT content detected in both the right and left striata observed in this study could be the answer to the behaviors observed and to the early alterations in dopamine in basal ganglia by 2,4-D in neonatal exposed rats, mediated by a serotonergic modulation on the dopaminergic system.

Lesion of substantia nigra pars compacta by the GluR5 agonist ATPA

Dopamine (DA) released by substantia nigra pars compacta (SNc) neurons is a key regulator of motor activity. A deficiency in the striatum DA content due to SNc degeneration is a characteristic of Parkinson's disease. The involvement of excitotoxic mechanisms in this pathology has been suggested. The kainate receptor subunit GluR5 has been identified in a few basal ganglia but it is strongly expressed in SNc. Here we examine whether (RS)-2-amino-3-(3-hydroxy-5-tbutylisoxazol-4-yl) propanoic acid (ATPA), a selective agonist of GluR5, induces damage in dopaminergic (DAergic) neurons. ATPA (13 nmol) was administered to rat SNc. Immediately after recovery from surgery, the rats displayed ipsilateral turning. This behavior disappeared in subsequent days. The administration of the D1/D2 agonist, apomorphine (1 mg/kg, s.c.) 1 and 2 weeks after ATPA-infusion also induced ipsilateral turning. Histological studies-performed 21 days after ATPA-infusion-showed a lesion of the lateral and central part of the SNc, where a significant loss (36%) of DAergic cells was detected by tyrosine hydroxylase immunohistochemistry. The lesion was restricted to the SNc, since no damage or glial reaction was observed in the substantia nigra pars reticulata as assessed by Nissl staining, tomato lectin staining for microglial cells and GFAP immunohistochemistry for astrocytes.

IN CONCLUSION

(1). ATPA-infusion induces neuronal damage in the SNc in the rat and (2). the behavioral effects of unilateral infusion of ATPA are consistent with DAergic alterations in basal ganglia.

Somatostatin modulates the behavioral effects of dopamine receptor activation in parkinsonian rats

Somatostatin may play a role in several neuropsychiatric disorders, including Parkinson's disease. Although functional interactions between somatostatinergic and dopaminergic transmitter systems have been well documented, no study has been conducted in animals with experimental Parkinsonism to explore the effects of somatostatin on dopamine receptor-mediated behavior. In the present study, rats with unilateral 6-hydroxydopamine-induced destruction of the medial forebrain bundle were assessed following administration of the dopamine(1/2) receptor agonist apomorphine. Ipsilateral intrastriatal infusion of somatostatin produced a dose-related inhibition of apomorphine-induced rotations with maximal effect at a dose of 7.5 microg in 2 microl. This inhibitory effect of somatostatin was antagonized by the somatostatin antagonist cyclo-somatostatin (0.1 microg in 2 microl, intrastriatally). Neither somatostatin (up to 15 microg in 2 microl) nor cyclo-somatostatin on its own induced rotations; similarly, this dose of cyclo-somatostatin did not affect apomorphine-induced rotations. From these results we suggest that exogenous somatostatin, by directly acting on its specific receptors in the striatum, inhibits the effects of dopamine receptor activation in parkinsonian rats. We conclude that therapies based on modulation of somatostatin may be worth exploring in the management of Parkinson's disease and other disorders of the basal ganglia.

Drug-induced rotation intensity in unilateral dopamine-depleted rats is not correlated with end point or qualitative measures of forelimb or hindlimb motor performance

The pharmacological induction of rotational (circling) behavior is widely used to assess the effects of lesions to the dopaminergic system and the success of treatment strategies in rat models of Parkinson's disease. While the number of rotations under apomorphine, L-DOPA and amphetamine is related to the extent of dopamine depletion after unilateral 6-hydroxydopamine lesion of the nigrostriatal dopamine system, the relationship of the intensity of rotational behavior to the degree of impairment in motor behavior is unclear. The present study examined this question by correlating rotational behavior and motor abilities in a rat analogue for Parkinson's disease produced by unilateral nigrostriatal bundle lesion with 6-hydroxydopamine. Ipsiversive and contraversive rotation was measured in the rats following systemic administration of low and high doses of apomorphine, the dopamine precursor L-DOPA, and amphetamine. The motor assessment included end point and qualitative measures of fore- and hindlimbs assessed in a skilled reaching task and a skilled ladder rung walking task. The intensity of drug-induced rotation did not correlate with the measures of motor performance. We conclude that independence of rotational behavior and motor performance argues that both the assessment of 6-hydroxydopamine behavioral deficits and potential treatments for the functional deficits require comprehensive assessment, including both measures of rotation and motor behavior.

A novel rotometer based on a RISC microcontroller

A new, low-cost rotometer, based on a reduced instruction set computer (RISC) microcontroller, is presented. Like earlier devices, it counts the number and direction of full turns for predetermined time periods during the evaluation of turning behavior induced by drug administration in rats. The present stand-alone system includes a nonvolatile memory for long-term data storage and a serial port for data transmission. It also contains a display for monitoring the experiments and has battery backup to avoid interruptions owing to power failures. A high correlation was found (r > .988, p < 2 x 10(-14)) between the counts of the rotometer and those of two trained observers. The system reflects quantitative differences in turning behavior owing to pharmacological manipulations. It provides the most common counting parameters and is inexpensive, flexible, highly reliable, and completely portable (weight including batteries, 159 g).

A novel black-hooded mutant rat (ci3) with spontaneous circling behavior but normal auditory and vestibular functions

Abnormal circling behavior in rodents is usually attributed to vestibular dysfunction. In rats, all circling mutants described previously have inner ear defects resulting in auditory and vestibular dysfunctions. Here, we describe a new mutant rat with abnormal spontaneous circling behavior but normal auditory and vestibular functions. The new circling mutant rat was discovered in progeny of an apparently normal black-hooded (BH) rat inbred line [BH.7A(LEW)/Won] and was termed ci3, because we recently found two other mutant circling rats (ci1 and ci2) in a Lewis (LEW) inbred rat strain. The ci3 mutant is characterized by circling behavior and locomotor hyperactivity, which occur in phases or bursts either spontaneously or in response to stress, e.g., when rats are transferred to a new environment. Video monitoring of undisturbed rats in their home cage during the light and dark periods showed that circling behavior is much more intense during the dark period, i.e., during the active phase of the animals. Most ci3 rats show a lateral preference in their rotational behavior, i.e., they either rotate to the left or to the right. Brainstem auditory evoked potential testing and different tests of vestibular function did not disclose any auditory or marked vestibular defects in ci3 rats. Furthermore, no morphological abnormalities were seen during histological examination of the cochlear and vestibular nuclei in the brainstem. Neurochemical determination of dopamine and dopamine metabolite levels in striatum, nucleus accumbens and substantia nigra showed that ci3 rats have a significant asymmetry in striatal dopamine in that dopamine levels were significantly lower in the hemisphere contralateral to the preferred direction of turning. Consistent with this finding, immunohistological examination of dopaminergic neurons in substantia nigra and ventral tegmental area yielded a significant laterality in the medial part of substantia nigra pars compacta with a lower density of tyrosine hydroxylase-positive neurons in the contralateral hemisphere of mutant circling rats, while no laterality was seen in unaffected rats of the background strain [BH.7A(LEW)/Won].Thus, the novel mutant ci3 rat exhibits several features which clearly differ from previously described circling rat or mouse mutants. The behavioral phenotype occurs in the absence of auditory or obvious vestibular defects and is most likely a consequence of lateralized abnormalities found in the nigrostriatal circuit. Apart from the use of ci3 rats for studying the functional lateralization of brain functions, the ci3 mutant may serve as a new model for movement disorders with abnormal lateralization.

Brainstem control of head movements during orienting; organization of the premotor circuits

When an object appears in the visual field, animals orient their head, eyes, and body toward it in a well-coordinated manner (orienting movement). The head movement is a major portion of the orienting movement. Interest in the neural control of head movements in the monkey and human have increased in the 1990's, however, fundamental knowledge about the neural circuits controlling the orienting head movement continues to be based on a large number of experimental studies performed in the cat. Thus, it is crucial now to summarize information that has been clarified in the cat for further advancement in understanding the neural control of head movements in different animal species. The superior colliculus (SC) has been identified as the primary brainstem center controlling the orienting. Its output signal is transmitted to neck motoneurons via two major separate pathways: one through the reticulospinal neurons (RSNs) in the pons and medulla and the other through neurons in Forel's field H (FFH) in the mesodiencephalic junction. The tecto-reticulo-spinal pathway controls orienting chiefly in the horizontal direction, while the tecto-FFH-spinal pathway controls orienting in the vertical direction. In each pathway, a subgroup of neurons functions as premotor neurons for both extraocular and neck motoneurons, while others are specified for each, which allows both coordinated and separate control of eye and head movements. Head movements almost always produce shifts in the center of gravity that might cause postural disturbances. The postural equilibrium may be maintained by transmitting the orienting command to the limb segments via descending axons of the reticulospinal and long propriospinal neurons. The SC and brainstem relay neurons receive descending inputs from higher order structures such as the cerebral cortex, cerebellum, and basal ganglia. These inputs may serve context-dependent control of orienting by modulating the activities of the primary brainstem pathways.

Differential effects of a small, unilateral, 6-hydroxydopamine-induced nigral lesion on behavior in high and low responders to novelty

The goal of this study was to develop an animal model that evaluates striatal-specific behavior after partial, unilateral destruction of nigrostriatal neurons. 6-OHDA (1 microg) was injected intranigrally (day 0) to reduce dopaminergic innervation of the dorsal striatum (DS); 6-OHDA (5 microg) was injected to reduce innervation of DS and nucleus accumbens (ACC). We analyzed changes in (a) behavior regulated by dopamine (DA) release in the DS (hindpaw preference from day 5 to day 19, every other day) and the ACC (novelty-induced locomotion on day 16) and (b) apomorphine-induced rotation (on day 21). We used two types of rat that show differences in structure and function of the dopaminergic neurons, namely high (HR) and low (LR) responders to novelty. 6-OHDA (1 microg) significantly decreased TH immunoreactivity (TH-ir) in the DS and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. Only in LRs was the significant increase of novelty-induced locomotion accompanied by a significant increase in TH-ir density in the ACC: this suggests a lesion-induced shift in nigrostriatal/mesolimbic balance toward a dominance of the mesolimbic system. The higher 6-OHDA dose significantly decreased TH-ir in the DS and the ACC and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. However, this increase occurred significantly earlier in LRs than in HRs. Apomorphine elicited contralateral rotations solely in LRs, and not in HRs, indicating development of supersensitive dopamine receptors in the DS of LRs, but not HRs. The data show that LRs are more susceptible to 6-OHDA than HRs. The relevance of the present data for Parkinson's disease is discussed.

Spontaneous circling behavior and dopamine neuron loss in a genetically hypothyroid mouse

The genetically hypothyroid mouse, Tshr(hyt), has a single point mutation resulting in a defective thyroid-stimulating hormone receptor, and therefore a non-functional thyroid gland. This is an autosomal recessive disorder and affected mice have been reported to have a number of somatic and behavioral deficits. This study reports a pronounced, spontaneous, asymmetrical circling behavior in the Tshr(hyt) mouse. The spontaneous circling behavior appeared in about 25% of the homozygous animals, in both males and females. The circling usually appeared by postnatal day 35 and continued throughout the lifespan of the animal. The circling was in one direction only, either clockwise or counterclockwise, with the directional preference being almost absolute. A stereological analysis of tyrosine hydroxylase immunoreactive neurons in the substantia nigra and adjacent ventral tegmental area of circling homozygous mice, non-circling homozygous mice and heterozygous mice revealed that the circlers had significantly fewer (40% reduction) midbrain dopamine neurons than those animals that did not circle. There was not an association between the direction of the circling and an asymmetry in the number of dopamine neurons in the midbrains of these mice. There was no difference in the number of dopamine neurons in the midbrain of the homozygous non-circlers and the heterozygous mice. These studies indicate that about 25% of genetically hypothyroid mice demonstrated a spontaneous, perseverative, unilateral circling behavior that was associated with a significant reduction in the number of their midbrain dopamine neurons. Thus congenitally hypothyroid mice are at risk for a reduction in the number of nigral dopamine neurons and an associated repetitive movement disorder.

Effects of rotational side preferences on immobile behavior of normal mice in the forced swimming test

It has been suggested that side preferences in spontaneous rotational behavior are determinant of differences in vulnerability to the effects of the learned helplessness paradigm. The purpose of the present study was to investigate the effects of side preferences of rotational behavior in another animal model of depression, the forced swimming test. Immobility was also investigated upon repeated testing sessions and in interaction with sex. Swiss mice (69 males and 73 females) were submitted to three sessions (test time = 5 min) of forced swimming. Immobile and turning behaviors were measured for each session and within each testing session. Consistency of laterality was defined considering the persistence of the same side turning preference in the three sessions. In general, there was an increase in immobility as test progressed and upon repeated testing sessions. Marked interindividual differences in mice immobile behavior were observed when consistency of laterality was considered. Consistent-right-turners presented greater immobility in the first session and better test-retest reliability, indicating that for this group, the adoption of immobile behavior was faster and more reliable over time. Immobility was higher for side-consistent males than for side-consistent females in the first session. This difference became even greater when consistent-right-turner males were compared to consistent-left-turner females. These results reinforce the idea that side preferences of spontaneous rotational behavior may account for interindividual differences in animal models of depression.

Spontaneous paroxysmal circling behavior in the ci2 rat mutant: epilepsy with rotational seizures or hyperkinetic movement disorder?

Circling, turning, rotating, spinning, wheeling, and cursive hyperkinesia are all synonymous terms used to describe the active movement of an animal in a circular direction. Circling behavior can be evoked by unilateral electrical and chemical stimulation or lesions of various brain sites, but can also occur after systemic drug administration or spontaneously in normal animals or mutant rodents. In humans, stereotypic body rotation can occur as a distinctive entity of generalized and focal epilepsy, and may be due to involvement of the striatum. We have previously described a Lewis rat mutant (ci2) with a behavioral phenotype characterized by lateralized circling, hyperactivity, opisthotonus, and ataxia. In these rats, circling occurs in phases or bursts either spontaneously or in response to stress. Neurochemical data indicate that the circling behavior of the ci2 mutants is related to an abnormal asymmetry in dopaminergic activity in the striatum. Because of the similarities to rotational epilepsy, we used video and electroencephalographic recordings to study whether the rotational behavior of the ci2 mutant rat is a result of a partial or generalized epilepsy. Epileptic WAG/Rij rats were used for comparison. Video monitoring of ci2 rats in the absence of any stress or disturbance showed that circling occurs in paroxysmal bursts during active wakefulness, but not during passive wakefulness or sleep. Circling was not preceded or followed by any convulsive motor seizures and was not associated with epileptiform abnormalities in the electroencephalogram, whereas WAG/Rij rats exhibited myoclonic seizures and epileptic spike-wave discharges during passive wakefulness and sleep. As a result of the association of circling with active wakefulness, ci2 rats exhibited many more rotations during the dark (active) phase compared with the light (rest) period. Increase in active wakefulness during the light phase by transfer of the rats to a new environment induced or intensified circling behavior. Most ci2 rats showed a consistent lateral preference during circling, but some rats changed their preference from one session to another. The data indicate that spontaneous paroxysmal circling behavior in the ci2 rat is not a consequence of epilepsy but reflects a hyperkinetic movement disorder with abnormal lateralization of brain function.

Alteration of second messengers during acute cerebral ischemia - adenylate cyclase, cyclic AMP-dependent protein kinase, and cyclic AMP response element binding protein

A variety of neurotransmitters and other chemical substances are released into the extracellular space in the brain in response to acute ischemic stress, and the biological actions of these substances are exclusively mediated by receptor-linked second messenger systems. One of the well-known second messenger systems is adenylate cyclase, which catalyzes the generation of cyclic AMP, triggering the activation of cyclic AMP-dependent protein kinase (PKA). PKA controls a number of cellular functions by phosphorylating many substrates, including an important DNA-binding transcription factor, cyclic AMP response element binding protein (CREB). CREB has recently been shown to play an important role in many physiological and pathological conditions, including synaptic plasticity and neuroprotection against various insults, and to constitute a convergence point for many signaling cascades. The autoradiographic method developed in our laboratory enables us to simultaneously quantify alterations of the second messenger system and local cerebral blood flow (lCBF). Adenylate cyclase is diffusely activated in the initial phase of acute ischemia (< or = 30 min), and its activity gradually decreases in the late phase of ischemia (2-6 h). The areas of reduced adenylate cyclase activity strictly coincide with infarct areas, which later become visible. The binding activity of PKA to cyclic AMP, which reflects the functional integrity of the enzyme, is rapidly suppressed during the initial phase of ischemia in the ischemic core, especially in vulnerable regions, such as the CA1 of the hippocampus, and it continues to decline. By contrast, PKA binding activity remains enhanced in the peri-ischemia area. These changes occur in a clearly lCBF-dependent manner. CREB phosphorylation at a serine residue, Ser(133), which suggests the activation of CREB-mediated transcription of genes containing a CRE motif in the nuclei, remains enhanced in the peri-ischemia area, which is spared of infarct damage. On the other hand, CREB phosphorylation at Ser133 rapidly diminishes in the ischemic core before the histological damage becomes manifest. The Ca2+ influx during membrane depolarization contributes to CREB phosphorylation in the initial phase of post-ischemic recirculation, while PKA activation and other signaling elements seem to be responsible in the later phase. These findings suggest that derangement of cyclic AMP-related intracellular signal transduction closely parallels ischemic neuronal damage and that persistent enhancement of this signaling pathway is important for neuronal survival in acute cerebral ischemia.

Auditory and vestibular defects in the circling (ci2) rat mutant

The circling rat is an autosomal recessive mutant (homozygous ci2/ci2) that displays lateralized circling behaviour, locomotor hyperactivity, ataxia and stereotypic head-movement. These abnormal behaviours occur in phases or bursts either spontaneously or in response to stress. Heterozygous (ci2/+) littermates display normal spontaneous behaviours. We have previously found that ci2/ci2 rats of both genders have a lower tissue content of dopamine in the striatum ipsilateral to the preferred direction of rotation, indicating that the rats turn away from the brain hemisphere with higher striatal dopaminergic activity. In view of the similarities of the motor syndrome of the ci2/ci2 mutant rat to that of mouse deafness mutants, the present study evaluated the hearing ability of the circling rat mutant by recording brainstem auditory-evoked potentials. To test for vestibular dysfunction, a swimming test was conducted. Histological methods were used to examine the cochlear and vestibular parts of the inner ear and the cochlear and vestibular brainstem nuclei for defects. The absence of auditory-evoked potentials demonstrated a complete hearing loss in the adult ci2/ci2 mutant rat, whereas heterozygous littermates exhibited auditory-evoked potentials with thresholds resembling those of other laboratory strains. Furthermore, the mutant rats were unable to swim. Histological analysis of the inner ear of adult mutants revealed virtually complete loss of the cochlear neuroepithelium, while no such hair cell degeneration was seen in the vestibular parts of the inner ear. However, part of the vestibular hair cells showed protrusions into the endolymphatic space, suggesting alterations in the cytoskeletal architecture. The histological findings in mutant circling rats strongly indicate that the hearing loss of the mutants is of the sensory neural type, the most prevalent type of hearing loss. In the cochlear nuclei of the brain stem of mutant rats, neurons exhibited an abnormal shape, reduced size and increased density compared to controls. In contrast, no abnormal neuronal morphology was seen in the vestibular nuclei, but a significantly reduced neuronal density was found in the medial vestibular nucleus. Abnormal vestibular function would be a likely explanation for the disturbed balance of mutant rats as exemplified by the ataxia and the inability to swim, whereas the previous data on these rats strongly indicate an involvement of the basal ganglia in the abnormal circling behaviour. The genetic defect in the mutant rats, thus, results in a clinical syndrome with features also seen in human genetic disorders with deafness and hyperkinesia, making the ci2/ci2 rat an excellent model for investigating both cochlear/vestibular dysfunction and hyperkinetic movement disorders.

Differential effects of unilateral striatal and nigrostriatal lesions on grip strength, skilled paw reaching and drug-induced rotation in the rat

Lateralised motor deficits associated with basal ganglia dysfunction were compared in separate groups of rats receiving unilateral 6-hydroxydopamine-induced lesions of the dopaminergic nigrostriatal pathway, quinolinic acid-induced lesions of the striatum, or sham control injections. Amphetamine induced ipsilateral rotation in both lesion groups, whereas a low ('supersensitive') dose of apomorphine induced rotation only in the nigrostriatal lesion group. Both lesions induced impairments in skilled paw reaching with the contralateral paw in the 'staircase' test; by contrast the striatal lesions also induced a marked impairment with the ipsilateral paw, which was unaffected by the nigrostriatal lesion. A previously reported increase in grip strength with the contralateral paw after nigrostriatal lesion was replicated, whereas striatal lesions induced only minor bilateral deficits in this test. The results are discussed in the context of the utility, reliability and validity of alternative tests of motor deficit in animal models of Parkinson's and Huntington's diseases.

Entopeduncular lesions facilitate and thalamic lesions depress spontaneous and drug-evoked motor behavior in the hemiparkinsonian rat

Pallidotomy is a neurosurgical procedure designed to ameliorate the akinesia and bradykinesia associated with Parkinson's disease. In the present study, the effects of pallidal-like lesions on motor behavior in the hemiparkinsonian rat were compared to the effects of lesions in the ventrolateral thalamus, a target of entopeduncular projections feeding motor-related information to motor cortex. Six aspects of spontaneous and evoked behavior induced by amphetamine and apomorphine in the hemiparkinsonian rat with either bilateral electrolytic entopeduncular lesions or bilateral electrolytic ventrolateral thalamic lesions were measured for 60 min. Saline or amphetamine, 5 mg/kg, or apomorphine, 0.3 mg/kg, were administered IP 5 min before the tests. The results show that on all measures except time spent resting the hemiparkinsonian rats with the entopeduncular lesions were more active than the hemiparkinsonian rats with the thalamic lesions. The asymmetrical rotation responses to dopamine receptor stimulation evoked by amphetamine and apomorphine were influenced by the general effect on gross motor behavior, as shown by the response being very large in the entopeduncular group and very small in the thalamic group. These results are consistent with current thinking about the functional organization of the basal ganglia according to which damage of the entopeduncular nucleus reduces its inhibitory control of the thalamic motor regions, thereby promoting thalamic facilitation of motor cortex, and damage to the thalamic motor regions has the opposite effect. These effects of the lesions translate, respectively, into hyperactivity and hypoactivity without blocking the asymmetrical rotation response of the hemiparkinsonian rat.

Activated phosphorylation of cyclic AMP response element binding protein is associated with preservation of striatal neurons after focal cerebral ischemia in the rat

Phosphorylation of the DNA-binding transcription factor, cyclic AMP response element binding protein, has recently been suggested to provide neuroprotective signals in times of cellular stress. Medium-sized striatal neurons are among the cells that are most vulnerable to ischemic stress in the brain. In the present study, phosphorylation of cyclic AMP response element binding protein was immunohistochemically evaluated in rat striatum in order to examine the ischemic vulnerability of each striatal region from the standpoint of cyclic AMP response element binding protein. Rats were subjected to 90-min focal cerebral ischemia followed by various periods of recirculation. Focal ischemia was induced by occlusion of the middle cerebral artery by the intraluminal suture method. Local cerebral blood flow measured by the 14C-iodoantipyrine method in the lateral and the medial striatal regions during occlusion was 5.0+/-7. 1 and 42.5+/-8.1ml/100g/min, respectively. Cerebral blood flow in each region was restored to the control level during the recirculation period. The lateral and the medial regions of the striatum in the sham animals showed hardly any immunoreactivity with the specific antibody against phosphorylated cyclic AMP response element binding protein. By contrast, at 3.5h of recirculation, a number of phosphorylated cyclic AMP response element binding protein-positive neurons were detected in the medial striatal region on the occluded side, and the increase in the number of immunopositive cells continued until two weeks of recirculation with gradual decline. The lateral striatal region on the ischemic side showed only a mild increase in phosphorylated cyclic AMP response element binding protein-positive cells at 3.5h of recirculation, and the immunoreactivity rapidly disappeared during the subsequent recirculation period. Appreciable increase in immunoreactive cells was also noted in the contralateral striatum during the early phase of recirculation, and this increase seemed to be associated with spontaneous circling movements of the animals. Cresyl Violet staining revealed that striatal neurons in the medial region remained intact until two weeks of recirculation, whereas neurons in the lateral striatal region soon showed ischemic damage, followed by complete neuronal loss, and evolution of a frank infarct. Immunoreactivity for bcl-2, apoptosis-suppressive protein, was clearly detected in many neurons in the medial striatal region, but no such immunoreactivity was detected in the lateral striatal region. These findings suggest that persistently activated phosphorylation of cyclic AMP response element binding protein in the striatum during post-ischemic recirculation may be closely associated with protection of striatal neurons on the ischemic side, while it may be associated with spontaneous circling movements on the contralateral side.

Melatonin protects against 6-OHDA-induced neurotoxicity in rats: a role for mitochondrial complex I activity

Unilateral injection into the right substantia nigra of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA) produces extensive loss of dopaminergic cells ('hemi-parkinsonian rat'). The pineal hormone melatonin, which is a potent antioxidant against different reactive oxygen species and has been reported to be neuroprotective in vivo and in vitro, was evaluated for potential anti-Parkinson effects in this model. Imbalance in dopaminergic innervation between the striata produced by intranigral administration of 6-OHDA results in a postural asymmetry causing rotation away from the nonlesioned side. Melatonin given systemically prevented apomorphine-induced circling behavior in 6-OHDA-lesioned rats. Reduced activity of mitochondrial oxidative phosphorylation enzymes has been suggested in some neurodegenerative diseases; in particular, selective decrease in complex I activity is observed in the substantia nigra of Parkinson's disease patients. Analysis of mitochondrial oxidative phosphorylation enzyme activities in nigral tissue from 6-OHDA-lesioned rats by a novel BN-PAGE histochemical procedure revealed a clear loss of complex I activity, which was protected against in melatonin-treated animals. A good correlation between behavioral parameters and enzymatic (complex I) analysis was observed independent of melatonin administration. A deficit in mitochondrial complex I could conceivably contribute to cell death in parkinsonism via free radical mechanisms, both directly via reactive oxygen species production and by decreased ATP synthesis and energy failure. Melatonin may have potential utility in the treatment of neurodegenerative disorders where oxidative stress is a participant.

Dopamine receptor gene transfer into rat striatum using a recombinant adenoviral vector: rotational behaviour

To study the role of dopamine (DA) receptor expression on dopamine-mediated rotational behaviour, adenovirus expressing the lacZ reporter gene (AdCMVLacZ) or D2R expressing adenoviral vector (AdRSVD2) viruses, mediating expression of beta-galactosidase and DAD2 receptors, respectively, were microinjected stereotactically into Sprague-Dawley rat striatum. Apomorphine stimulated rotational behaviour was measured in rats unilaterally injected with either AdCMVLacZ or AdRSVD2. No significant difference in rotational direction was observed until day 14 post-injection, when animals showed a tendency to rotate away from the injected side. Our data indicate that unilateral changes in receptor density mediated by a non-cell type selective adenoviral vector results in minor changes in rotational behavior. This suggests that supersensitivity in dopamine receptor signaling, rather than receptor levels per se, are the major factor in determining rotational response with dopamine agonist stimulation in unilateral striatal dopamine depleted animals.

Temporal changes of dopaminergic and glutamatergic receptors in 6-hydroxydopamine-treated rat brain

Quantitative receptor autoradiography was used to examine the sequential patterns of changes in dopaminergic and glutamatergic receptors in the brain of rats lesioned with 6-hydroxydopamine. The animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks of postlesion. Degeneration of the nigrostriatal pathway caused a significant increase in dopamine D(2) receptors in the ipsilateral striatum from 1 to 8 weeks of postlesion. In the ipsilateral substantia nigra (SN), a significant decrease in dopamine D(2) receptors was also observed from 1 to 8 weeks of postlesion. On the other hand, dopamine D(1) receptors were increased in the ipsilateral ventromedial striatum from 2 to 4 weeks of postlesion. In the ipsilateral SN, a transient increase in dopamine D(1) receptors was observed only 1 week after lesioning. However, other regions in both ipsilateral and contralateral sides showed no significant change in dopamine D(1) and D(2) receptors during postlesion except for a transient change in a few regions. N-Methyl-D-aspartate (NMDA) receptors showed no significant changes in all brain regions studied during the postlesion. In contrast, a transient increase in excitatory amino acid transport sites was observed only in the frontal cortex and ventromedial striatum of the ipsilateral side at 2 weeks of postlesion. However, glycine receptors showed a significant change in any brain areas of both ipsilateral and contralateral sides after lesioning. The change in the brain areas of contralateral side was more pronounced than that of ipsilateral side for glycine receptors. In addition, dopamine uptake sites showed a severe damage in the ipsilateral striatum from 1 to 8 weeks after lesioning. In the contralateral side, in contrast, no significant change in dopamine uptake sites was found in the striatum during the postlesion. These results indicate that unilateral injection of 6-hydroxydopamine in the medial forebrain bundle can cause a significant increase in dopamine D(1) and D(2) receptors in the striatum. The increase in dopamine D(2) receptors was more pronounced than that in dopamine D(1) receptors in the striatum after 6-hydroxydopamine treatment. In contrast, dopamine uptake sites showed a severe damage in the striatum during the postlesion. Furthermore, our results support the existence of dopamine D(2) receptors on the neurons of SN, but not dopamine D(1) receptors. For glutamatergic receptor system, the present study suggests that the changes in glycine receptors may be more susceptible to degeneration of nigrostriatal pathway than NMDA receptors and excitatory amino acid transport sites. Thus, our findings are of interest in relation of degeneration of the nigrostriatal pathway that occurs in Parkinson's disease

Development of an adenoviral vector for intracerebral delivery of the dopamine D(2) receptor

The age-related loss of striatal dopamine D(2) receptors (D(2)R) has been observed in numerous species, including rodents, monkeys, and man, and is partly responsible for impaired motor function in aged mammals. We have developed an adenoviral vector designed for intracerebral transfer of cDNA for D(2)R. Results of in vitro studies demonstrated that the vector produced abundant message for D(2)R and that the vector was membrane bound and capable of binding appropriate ligand. Results of in vivo studies provided clear evidence of D(2)R production when injected into the striatum of rats. The D(2)R produced were capable of binding appropriate ligand. In addition, evidence of functional receptors was produced by demonstrating apomorphine-induced rotational behavior in rats receiving a unilateral injection of the vector. Despite these successes, we have been unable to demonstrate improvement in the motor behavior of aged rats receiving bilateral injections of the vector. A major problem with this vector as with similar adenoviral vectors is the loss of expression beginning 3-5 days after injection to undetectable levels at 21 days. Because of the lack of motor functional effects in aged rats and the loss of expression of the vector, other strategies for development of the vector are being pursued. Regarding functional effects, we have examined the feasibility of manipulating hippocampal acetylcholine (ACh) release through D(2)R manipulation to improve memory performance. Using microdialysis, we have demonstrated in vivo in rats that treatment with a D(2)R agonist increases hippocampal ACh release while treatment with a D(2)R antagonist attentuates this effect as well as impairs performance in a complex maze task. In addition, a D(2)R null mutant mouse is being used to examine possible therapeutic effects of the vector. These mice show specific motor deficits. Recent studies using positron emission tomography have also demonstrated the feasibility of in vivo imaging of the vector. Thus, use of adenoviral vectors specific for neurotransmitter receptors can provide a highly useful research tool for examining age-related alterations in behavioral function and a possible strategy for therapeutic intervention.