The organization of the projection from the cerebral cortex to the striatum in the rat

Transection of corticostriatal afferents reduces amphetamine- and apomorphine-induced striatal Fos expression and turning behaviour in unilaterally 6-hydroxydopamine-lesioned rats

Corticofugal fibres from the prefrontal, prelimbic and anterior sensorimotor cortices were transected by a wide coronal knife-cut through the forceps minor. The cut was performed on the dopamine-depleted side of unilaterally 6-hydroxydopamine-lesioned rats, or on either the right or the left side of intact rats. Sham-lesioned controls received a superficial cortical cut at the same level. Seven days after surgery, apomorphine (0.25 mg/kg s.c.) was administered to 6-hydroxydopamine-lesioned animals and D-amphetamine (5 mg/kg i.p.) was administered to the non-dopamine-denervated ones. Two hours later, the animals were perfusion-fixed for the immunohistochemical detection of the nuclear protein Fos. A computerized image analysis technique was used to quantify, bilaterally, striatal Fos expression in 11 areas of the striatum. The frontocortical transection reduced both apomorphine- and amphetamine-induced Fos expression by 33-66% within the ipsilateral caudate-putamen. The effect was observed throughout the rostral portion of the striatal complex, where the lesioned cortical fibres terminate most densely. A separate batch of unilaterally 6-hydroxydopamine-lesioned rats were used to test the effect of frontocortical transection on amphetamine- and apomorphine-induced turning behaviour. Two groups of rats, showing similar rates of contralateral turning (7-8 turns/min) in response to apomorphine (0.25 mg/kg s.c.), were subjected to either a complete frontocortical transection or a sham lesion on the dopamine-denervated side. An additional two groups, showing comparable rates of ipsilateral turning (15 turns/min) in response to amphetamine (5 mg/kg i.p.), received similar lesions, but now on the side ipsilateral to the intact dopaminergic innervation.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of rat striatal neurons during performance of a lever-release version of the conditioned avoidance response task

Neural activity was recorded from 218 sites in the striatum (caudate-putamen and nucleus accumbens) of rats trained on a lever-release version of the conditioned avoidance response (CAR) task, in which an auditory signal elicits a short-latency, forelimb withdrawal. > 80% of these recording sites showed task-related activity, including neurons that responded to the auditory stimulus (signal-related cells), the lever-release (response-related cells), or both of these events (signal/response-related cells). Histological analysis revealed a predominance of signal-related neurons in medial striatum, whereas lateral recording sites mainly showed response-related activity. Haloperidol (0.1 mg/kg s.c.), a widely used neuroleptic that impairs CAR performance, significantly attenuated task-related neural activity without altering the latency of the neural response or spontaneous firing rate. Collectively, these results, which demonstrate the usefulness of the lever-release CAR paradigm for assessing striatal function, suggest that the sensory and motor aspects of the CAR task are processed by different striatal regions. Moreover, haloperidol appears to disrupt the striatal processing of both sensory and motor information.

Spatial distributions of chemically identified intrinsic neurons in relation to patch and matrix compartments of rat neostriatum

The spatial distributions and dendritic branching patterns of chemically identified subpopulations of striatal intrinsic neurons, defined by immunoreactivity for choline acetyltransferase (ChAT), neuropeptide Y or parvalbumin, were studied in relation to patch and matrix compartments of rat neostriatum. ChAT-immunoreactive cells and fibers showed an uneven pattern of distribution in the striatum. ChAT immunoreactivity was higher in the dorsolateral part and lower in the ventromedial part of the striatum. This regional gradient pattern is the inverse of the overall pattern of calbindin D28k immunoreactivity. However, in small regions close to the lateral ventricle and globus pallidus, areas containing fewer ChAT-immunoreactive cells and fibers coincided with those containing low calbindin D28k immunoreactivity. Neuropeptide Y immunoreactivity was uniform in the neostriatum. Certain neuropeptide Y cells (about 20%) were also immunoreactive for calbindin D28k, indicating that at least a small population of calbindin D28k-immunoreactive cells are medium aspiny cells. Parvalbumin immunoreactivity was not uniform in the striatum. A higher density of parvalbumin immunoreactivity was found in the neuropil in lateral and caudal parts than in the medial part. Small regions with weaker parvalbumin-immunoreactive neuropil partially corresponded to calbindin D28k poor patches. Larger cells immunoreactive for parvalbumin were preferentially located in lateral and caudal parts of the striatum. Cells immunoreactive for ChAT, neuropeptide Y or parvalbumin showed basically similar distribution patterns in relation to the patch and matrix compartments. Most stained cells were located in the matrix, but some were located at the borders of patches and a few were inside patches. Most primary dendrites of stained cells in the matrix or patches remained confined to these compartments, but cells on the borders invariably extended dendrites into both compartments. The striatal intrinsic neurons form chemically differentiated neuronal circuits within the matrix, and the patches and those whose dendrites cross the borders may contribute to associational interconnections between the two compartments, unlike the spiny projection neurons whose dendrites are confined to one or the other compartment.

Prefrontal cortical dopamine systems and the elaboration of functional corticostriatal circuits: implications for schizophrenia and Parkinson's disease

The dopaminergic innervation of the prefrontal cortex is able to transsynaptically regulate the activity of subcortical dopamine innervations. Disruption of the prefrontal cortical DA innervation results in the enhanced biochemical responsiveness of the dopamine innervation of the nucleus accumbens. We present recent data indicating that distinct prefrontal cortical dopamine innervations can be functionally dissociated on the basis of responsiveness to stress. The ventral striatal projection target (nucleus accumbens shell) of the prefrontal cortical region that is stress sensitive is also responsive to stress. In this manner interconnected cortico-striato-pallido-mesencephalic loops can be defined on the basis of the biochemical responsive of local dopamine systems to stress and on the basis of responsiveness to antipsychotic drugs. These data suggest the functional derangement of a distinct corticofugal loops in schizophrenia and in certain aspects of Parkinson's disease.

Disordered dopamine neurotransmission in the striatum of rats undergoing pilocarpine-induced generalized seizures, as revealed by microdialysis

In this study rats were fitted with a concentric dialysis probe in one striatum and extracellular concentrations of dopamine and HVA measured by reverse phase high performance liquid chromatography. Injections of saline or the D1 agonist SKF 38393 (30 mg/kg) did not affect the releases of these compounds. On the other hand, the D2 agonist LY 171555 (0.5 mg/kg) inhibited the release of both dopamine and HVA, whilst amphetamine (1 mg/kg) increased the output of dopamine but not HVA. Treatment with 200 mg/kg pilocarpine caused minimal signs of epileptic activity and did not affect striatal dopamine neurotransmission. Concomitant administration of SKF 38393 (30 mg/kg) to this dose of pilocarpine greatly facilitated the incidence and severity of motor seizures, which were accompanied by an irregular pattern of dopamine release and a significant rise in HVA overflow. Similar results were obtained with rats made to convulse with 400 mg/mg pilocarpine, and to a lesser extent if these animals were first pretreated with a protective dose of LY 171555 (0.5 mg/kg). It is concluded that dopamine neurotransmission in the striatum is disrupted in rats undergoing a pilocarpine-induced motor seizure, and that the extent of this disruption increases as the seizure becomes more severe. An irregular release of dopamine could signify a loss of sensorimotor control by the striatum, which might conceivably contribute to the intractability of the seizure. An increase in the dialysate concentrations of metabolite and not dopamine, is consistent with a heightened glutamate-stimulated release of dopamine from a discrete striatal pool, caused by the seizure spreading through the cortex and activating the cortico-striatal system.

Discrete quinolinic acid lesions of the lateral but not of the medial caudate-putamen reversed haloperidol-induced catalepsy in rats

Discrete lesions in the medial or lateral subregion of the rostral caudate-putamen (CP) were induced by bilateral intracerebral injections of a low dose of quinolinic acid (30 nmol in 1 microliter/per side) in rats. Quinolinic acid lesions in the lateral CP potently reversed haloperidol-induced catalepsy (0.5 mg/kg,i.p.), while lesions in the medial CP were not effective. Spontaneous locomotor activity was not altered significantly after quinolinic acid lesions of either the medial or lateral CP. These results show that the lateral CP seems to be important for the expression of neuroleptic-induced catalepsy and thus further corroborate the concept of a functional heterogeneity of the striatum.

Cortical regulation of subcortical dopamine systems and its possible relevance to schizophrenia

A unique model of DA system regulation is presented, in which tonic steady-state DA levels in the ECF act to down-regulate the response of the system to pulsatile DA released by DA cell action potential generation. This type of regulation is similar in many respects to the phenomenon proposed to mediate the action of norepinephrine on target neurons; i.e., an increase in the "signal-to-noise" ratio as measured by postsynaptic cell firing (Freedman et al., 1977; Woodward et al., 1979). However, in this model the signal and the noise are neurochemical rather than electrophysiological. Furthermore, the "noise" (tonic DA in the ECF) actually down-regulates the "signal" (phasic DA release) directly, and thereby provides a "signal" of its own that affects the system over a longer time-course. Therefore, the difference between signal and noise may also depend on the time frame under which such determinations are made.

Role of the corpus callosum in expression of behavioral asymmetries induced by a unilateral dopamine lesion of the substantia nigra in the rat

The present study examines the effects of sectioning the corpus callosum on the expression of asymmetric behaviors induced by a unilateral 6-hydroxydopamine (6-OHDA) lesion of the substantial nigra. Severing the corpus callosum eliminated the asymmetry in spontaneous investigation of edges in an open-field, without affecting total time of investigation. In contrast, callosotomy reduced the magnitude of externally cued turning, but failed to affect the directional distribution of responding. Moreover, it reduced the magnitude of apomorphine- but not amphetamine-induced turning. It is suggested that transcallosal communication is required for those behavioral asymmetries induced by a unilateral dopamine lesion which depend on head, rather than whole body movements.

Ventrolateral striatal dopamine depletions impair feeding and food handling in rats

The present study was conducted to characterize the changes in feeding behavior produced by localized depletion of dopamine (DA) in the nucleus accumbens and subregions of the neostriatum in the rat. Food-deprived rats were given at least 2 weeks of training, which consisted of being placed in a Plexiglas box and being given 15-18 g of food for a 30-min session. After the training period, rats received bilateral injections of the neurotoxic agent 6-hydroxydopamine (6-OHDA) into the nucleus accumbens, ventromedial striatum, or ventrolateral striatum. Observations were made in 30-min tests on days 3 and 7 after surgery, and measures were obtained for total food intake, time spent feeding, rate of feeding, and forepaw usage during feeding. The ventrolateral striatum was the only site at which dopamine depletion altered aspects of food intake. Rats with ventrolateral striatal DA depletion had reductions in food intake, decreases in the rate of feeding, and impaired forepaw usage during feeding. Time spent feeding was not significantly affected by DA depletion. Water consumption was significantly reduced by DA depletions in the ventrolateral striatum but not by depletions at other sites. These results indicate that ventrolateral striatal DA depletions decrease food intake by impairment of motor functions necessary for the performance of feeding behavior.

Characterization of GABA release from intrastriatal striatal transplants: dependence on host-derived afferents

Extracellular levels of GABA, derived from cell suspension transplants of embryonic day 14-15 rat striatal primordia implanted into the previously excitotoxically lesioned striatum, were measured using intracerebral microdialysis in halothane-anaesthetized rats. GABA overflow was monitored using loop type dialysis probes implanted into grafted, age-matched ibotenic acid-lesioned and intact striata, under baseline conditions and after different pharmacological manipulations. Basal and evoked GABA release, which was reduced by 58 and 96%, respectively, in the excitotoxin-lesioned striatum, was restored by the striatal grafts to levels close to or above those observed in normal striata. The graft-derived release of GABA was most likely of neuronal origin, since the K(+)-evoked (100 mM) GABA overflow was reduced by almost 80% when Ca++ was replaced by 20 mM Mg++ in the perfusion medium, and blockade of GABA uptake by nipecotic acid (0.5 mM), induced a greater than six-fold increase in GABA overflow. However, perfusion of the graft with 1 microM tetrodotoxin in combination with K+ (100 mM) resulted in little if any reduction in the K(+)-evoked overflow. Histological analysis demonstrated a dense tyrosine hydroxylase-positive fibre network in the grafts, which was removed after a 6-hydroxydopamine lesion of the ipsilateral nigrostriatal pathway. The dopamine denervating lesion resulted in an increased K(+)-evoked GABA overflow both in the intact (+76%) and the grafted striata (+181%), suggesting that the tonic dopaminergic inhibitory control of GABA release, seen in the intact striatum, is also present in the grafted striata. The glutamate analogue, kainic acid (1 mM added to the perfusion fluid), evoked a 60-74% increase in GABA overflow both in intact striata (with or without dopaminergic denervation) and in the striatal grafts. This effect seemed to be dependent on an intact corticostriatal projection, since knife-cut transections of the frontal cortex at the level of the forceps minor, abolished the response in both the intact and grafted striata. These results demonstrate that grafts of fetal striatal tissue implanted into the excitotoxically lesioned striatum restore striatal GABA overflow in a neuron-dependent manner, close to or above that seen in the normal intact striatum. Furthermore, the graft-derived GABA release appears to be under normal regulatory control from the host dopaminergic and glutamatergic systems. Since the GABAergic striatal output system is critical for the expression of striatum-related behaviours, it is proposed that the graft-induced behavioural recovery in the striatal lesion model, at least in part, may depend on the restoration of striatal GABAergic neurotransmission.

Prediction of specific damage or infarction from the measurement of tissue impedance following repetitive brain ischaemia in the rat

The development of irreversible brain damage during repetitive periods of hypoxia and normoxia was studied in anaesthetized rats with unilateral occlusion of the carotid artery (modified Levine model). Rats were exposed to 10 min hypoxia and normoxia until severe damage developed. As indices of damage, whole striatal tissue impedance (reflecting cellular water uptake), sodium/potassium contents (due to exchange with blood). Evans Blue staining (blood-brain barrier [BBB] integrity) and silver staining (increased in irreversibly damaged neurons) were used. A substantial decrease in blood pressure was observed during the hypoxic periods possibly producing severe ischaemia. Irreversibly increased impedance, massive changes in silver staining, accumulation of whole tissue Na and loss of K occurred only after a minimum of two periods of hypoxia, but there was no disruption of the BBB. Microscopic examination of tissue sections revealed that cell death was selective with reversible impedance changes, but became massive and non-specific after irreversible increase of the impedance. The development of brain infarcts could, however, not be predicted from measurements of physiological parameters in the blood. We suggest that the development of cerebral infarction during repetitive periods of hypoxia may serve as a model for the development of brain damage in a variety of clinical conditions. Furthermore, the present model allows the screening of potential therapeutic measuring of the prevention and treatment of both infarction and selective cell death.

Effect of the neurotoxin AF64A on intrinsic and extrinsic neuronal systems of rat neostriatum measured by in vivo microdialysis

In the present in vivo microdialysis study the aziridinium ion of ethylcholine mustard, AF64A and the excitotoxin ibotenic acid were compared for their effects on extracellular striatal acetylcholine, choline, gamma-aminobutyric acid (GABA), dopamine and its metabolites, glutamate and aspartate, measured in the same perfusate sample, under basal and high KCL conditions. Ten days following unilateral striatal injections of AF64A (2 x 0.08 to 2 x 8 mM) there was a dose-dependent decrease in the extracellular striatal levels of acetylcholine and GABA, the two major intrinsic striatal neurotransmitter systems. No significant effects were observed on any of the monitored neurotransmitter systems following the lowest (2 x 0.08 mM) dose of AF64A, while at the intermediate (2 x 0.8 mM) dose, AF64A produced a unilateral > 50% and > 70% decrease in basal extracellular striatal acetylcholine and GABA levels respectively. The effects of K(+)-depolarization on extracellular acetylcholine and GABA levels were diminished by approximately 50%. At the highest dose (2 x 8 mM), extracellular striatal acetylcholine levels were non-detectable under basal conditions, while the GABA levels were decreased by > 50%, when compared with the contralateral intact side. However, at this dose, GABA levels were bilaterally decreased compared to levels observed in control animals. Basal extracellular striatal dopamine and glutamate levels, representing the two major extrinsic neurotransmitter systems innervating the neostriatum were only affected by the highest dose of AF64A. The excitotoxin ibotenic acid (2 x 28.4 mM) produced a strong unilateral decrease in extracellular striatal acetylcholine (> 80%) and GABA (> 90%) levels, without significantly affecting basal dopamine and glutamate levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in size of the caudate nucleus of the cat after a prenatal neocortical lesion

In order to study the influence of prenatal developmental factors upon reaction of the brain to injury, fetal kittens (E43-48) were lesioned in the frontal or parietal cortex unilaterally and maintained into young adulthood. The animals were sacrificed by perfusion with an aldehyde fixative or by an overdose of pentobarbital. Frozen sections were cut and stained with thionin. These sections were used for calculation of caudate nuclei volumes and for measurements of neuronal and glial cell packing density and neuronal cell body size. Island and matrix compartments were sampled separately. We found that the volume of the ipsilateral caudate nucleus had significantly increased as compared to (a) the volume of the corresponding nucleus in intact cats (mean, 15%) and (b) the nucleus contralateral to the lesion (mean, 7.6%). The latter nucleus also tended to a volume increase (mean, 8.1%). The cytoarchitecture of the caudate nuclei was essentially unchanged with two exceptions. The neuronal cell packing density in the matrix compartment of the contralateral side was decreased (mean, 14.9%) while the size of neuronal cell bodies in the island compartment of the nucleus ipsilateral to the lesion was smaller (mean, 5%) relative to controls. These findings suggest that the number of neurons in the caudate of lesioned animals was larger than in intact controls, particularly on the lesioned side of the brain. This might be due to a reduction of naturally occurring cell death during development.

Striatal regulation of morphine-induced hyperphagia: an anatomical mapping study

Both systemic and intracranial administration of morphine can result in spontaneous feeding in non-deprived rats. The present investigation was conducted to examine the involvement of the striatum in this phenomenon. Morphine sulfate (0, 0.5, 1.0, 5.0, 10.0, and 20.0 micrograms/0.5 microliters) was microinjected into five discrete striatal subregions in non-deprived rats: the nucleus accumbens, the ventromedial striatum, the ventrolateral striatum, the anterior dorsal striatum, and the posterior dorsal striatum. Feeding, drinking, locomotion, rearing, and food intake were measured over 4 h after infusion. Results indicate that the striatum is a heterogeneous structure with regard to the regulation of opiate-induced feeding behavior and locomotor activity. Morphine infusion into anteroventromedial regions including the nucleus accumbens resulted in a marked hyperphagia that was generally delayed in onset; much smaller increases or no change in feeding occurred after administration into more dorsal, lateral and posterior areas. It is hypothesized that there may exist within the striatum an anatomical gradient that is most sensitive to opiate-induced feeding within the anteroventromedial sector. Since this area has extensive connections with other brain sites sensitive to opiate-induced feeding, it may be a critical part of an opiatergic feeding system within the brain. In addition, a possible role for the anteroventromedial striatum in compulsive feeding and bulimia is discussed.

Grafts in the treatment of Parkinson's disease: animal models

Long-term treatment of parkinsonian patients with L-DOPA leads to a loss of efficacy over time and the appearance of important side effects such as dyskinesias. Grafts of chromaffin cells of the adrenal medulla or fetal ventral mesencephalic neurons bring behavioral improvement in animal models of Parkinson's disease. These improvements are likely to be related to the secretion of dopamine by the grafted cells and/or to the reinnervation of the host tissue. In addition, a leak in the blood-brain barrier may allow peripheral catecholamines to gain access to the brain. Lack of clear effects of grafts in parkinsonian patients may be due to their poor survival in the human brain. Improvement of grafting techniques as well as the addition of neurotrophic factors to grafts may help increase their survival and improve behavioral effects. Recently, genetic techniques have allowed the creation of genetically modified cell lines which can produce L-DOPA and these cells may be grafted in the brain. Interestingly, these cell lines may be encapsulated in permselective membranes which can protect them from immunological rejection and avoid the uncontrolled cell growth of these mitotically active cells. Grafting techniques seem to be an interesting alternative to treat parkinsonian patients. Improvement of grafting procedures may help increase survival of grafts and thus enhance behavioral improvements. Moreover, genetic modification of well-known tumor cell lines or patient's own cells such as astrocytes may help avoid the low availability as well as ethical and immunological problems linked to the use of fetal human tissue.

Immunohistochemical evidence for a crossed cholecystokinin corticostriatal pathway in the rat

Using the indirect immunofluorescence technique, the effects of decortication and callosotomy on the pattern of cholecystokinin (CCK)-like immunoreactivity were studied in the striatum of the rat. Decortication plus callosotomy, but not decortication alone, caused a strong decrease in the immunoreactivity on the side ipsilateral to the lesion. An almost complete disappearance of CCK immunoreactive patches in the medial-dorsal aspects of the striatum was observed. These results indicate that part of the striatal CCK immunoreactive fibres are of cortical origin, to a considerable extent from the contralateral side.

Behavioral and neurochemical indices of barrel cortex-basal ganglia interaction

Previous experiments from our laboratory have shown a wide variety of time-dependent lateralized changes in behavior and nigrostriatal function following unilateral manipulation of the mystacial vibrissae of rats. The present experiment investigated the effects of unilateral radiofrequency lesion of the cortical vibrissae representation (the barrel fields) in light of these results. We measured lateralized changes in behavior as well as tissue monoamines in neostriatum and substantia nigra, between 1 and 16 days post-lesion. Short-term asymmetries in exploratory behavior (thigmotactic scanning) and neostriatal serotonin metabolism that lasted up to day 6 were seen. In substantia nigra, time-related asymmetries in dopamine concentrations were found with higher ipsilateral values on day 3 and higher contralateral values on day 6. After day 6, the animals had recovered from these acute effects and thereafter, neostriatal dopamine metabolism became asymmetrical. Also during this time, they showed a directional bias in spontaneous and apomorphine-induced turning. Finally, neostriatal serotonin was bilaterally elevated on day 16. These results parallel some of the effects previously seen following unilateral removal of the vibrissae, indicating that the barrel cortex is a critical link in the functional interaction between the vibrissae and basal ganglia.

Developmental regulation of phosphoprotein gene expression in the caudate-putamen of rat: an in situ hybridization study

The regional and cellular ontogeny of the mRNA encoding the dopamine- and cAMP-regulated phosphoprotein, DARPP-32, has been studied in rat striatum by quantitative in situ hybridization histochemistry. The mRNA for DARPP-32 exhibited a characteristic developmental profile. The hybridization signal was first visible on the day of birth, at which time DARPP-32 mRNA was concentrated in patches in the caudate-putamen. By the end of the first postnatal week, the majority of neurons in the caudate-putamen expressed the DARPP-32 message. Levels of mRNA per cell increased markedly during the second postnatal week, and peaked around the beginning of the third week. The adult level of DARPP-32 mRNA was lower than that observed at the apex of mRNA expression, on a per cell basis, while the proportion of neurons expressing detectable levels of message remained relatively constant. In the nucleus accumbens and olfactory tubercle, DARPP-32 mRNA development lagged somewhat behind that observed in the caudate-putamen, but was similar in other respects. A non-quantitative study employing an oligonucleotide probe complementary to the mRNA encoding another cAMP-regulated phosphoprotein, ARPP-21, revealed a similar developmental sequence to DARPP-32. The present results suggest that for DARPP-32 mRNA, genetic and, possibly, environmental factors play a role in determining the developmental patterns observed.

Subcortical deterioration after cortical damage: effects of diazepam and relation to recovery of function

Agents which enhance the activity of gamma-aminobutyric acid (GABA) can severely disrupt behavioral recovery in rats following damage to the neocortex if delivered during a sensitive postoperative period. The mechanisms of this disruption have not been found. It has been suggested previously that the ipsilateral striatum and related structures may be transiently disabled after cortical lesions and that diazepam may interfere with restoration of function in these areas. In the present experiment, the subcortical anatomical effects of chronic (3 weeks) administration of diazepam, an indirect GABAergic agonist, were assessed following unilateral lesions of the anteromedial cortex (AMC) or the sensorimotor cortex (SMC) in rats. Atrophic and degenerative changes were examined in the striatum, substantia nigra and thalamus. Following either AMC or SMC lesions, there was a reduction in the size of the ipsilateral striatum and thalamus and a loss of neurons in the ipsilateral substantia nigra pars reticulata (SNr). After AMC lesions, striatal atrophy and neuron loss in the SNr were increased by the diazepam regimen relative to vehicle-treated controls. In addition, diazepam interfered with the behavioral recovery from somatic-sensorimotor asymmetries in AMC-lesioned rats. After SMC lesions, the sites of striatal and thalamic atrophy were different from that observed after AMC lesions, and the extent of atrophy and neuron loss was not exaggerated by diazepam treatment. Consistent with these data, diazepam did not significantly affect recovery from SMC lesions. These findings suggest that the long-term disruptive effects of diazepam on recovery of function after AMC lesions may be related to an augmentation of lesion-induced degeneration.

The depolarization block hypothesis of neuroleptic action: implications for the etiology and treatment of schizophrenia

Antipsychotic drugs are known to block dopamine receptors soon after their administration, resulting in an increase in dopamine neuron firing and dopamine turnover. Nonetheless, antipsychotic drugs must be administered repeatedly to schizophrenics before therapeutic benefits are produced. Recordings from dopamine neurons in rats have revealed that chronic antipsychotic drug treatment results in the time-dependent inactivation of dopamine neuron firing via over-excitation, or depolarization block. Furthermore, the clinical profile of the response to antipsychotic drugs appears to correspond to the dopamine system affected: antipsychotic drugs that exert therapeutic actions in schizophrenics inactivate dopamine neuron firing in the limbic-related ventral tegmental area, whereas drugs that precipitate extrapyramidal side effects cause depolarization block of the motor-related substantia nigra dopamine cells. One factor that remains unresolved with regard to the actions of antipsychotic drugs is the relationship between dopamine turnover and depolarization block--i.e., why does a significant level of dopamine release or turnover remain after antipsychotic drug treatment if dopamine cells are no longer firing? We addressed this question using an acute model of neuroleptic-induced depolarization block. In this model, dopamine cells recorded in rats one month after partial dopamine lesions could be driven into depolarization block by the acute administration of moderate doses of haloperidol. However, similar doses of haloperidol, which were effective at increasing dopamine levels in the striatum of intact rats, failed to change dopamine levels in lesioned rats. This is consistent with a model in which neuroleptic drugs exert their therapeutic effects in schizophrenics by causing depolarization block in DA cells, thereby preventing further activation of dopamine neuron firing in response to external stimuli. Thus, attenuating the responsivity of the dopamine system to stimuli may be more relevant to the therapeutic actions of antipsychotic drugs than receptor blockade or decreases in absolute levels of dopamine, which could presumably be circumvented by homeostatic adaptations in this highly plastic system.

Paradoxical increase in striatal neuropeptide gene expression following ischemic lesions of the cerebral cortex

Ischemic lesions of the cerebral cortex occur frequently in humans as a result of stroke. One major consequence of the death of cortical neurons is the loss of excitatory cortical projections to subcortical regions. Little is known, however, about the transsynaptic effect of such lesions on neurotransmitter expression in subcortical structures. We have examined the effects of ischemic cortical lesions on the peptidergic neurotransmitters enkephalin and tachykinins in the striatum, a brain region massively innervated by glutamatergic cortical inputs. The levels of enkephalin and tachykinin mRNAs increased in the striatum of adult rats after thermocoagulation of pial vessels. The effects were more pronounced in the striatal region most heavily innervated by the lesioned cortex but were also observed in other striatal regions and on the contralateral side. Increased gene expression was accompanied by increased immunoreactivity for the two peptides. Elevated levels of enkephalin mRNA were observed up to 3 months after surgery in the ipsilateral striatum. Whereas results of previous studies of acute cortical ablations suggested that excitatory corticostriatal neurons were necessary to maintain normal peptide levels in striatal efferent neurons, the present data indicate that lesions of the same corticostriatal neurons secondary to local ischemia result in a paradoxical transsynaptic activation of neuropeptide synthesis in subcortical structures. This effect may play a role in the functional consequences of cortical strokes and progressive cortical atrophy in humans and may have critical bearing for their treatment and prognosis.

Synaptic organization of GABAergic inputs from the striatum and the globus pallidus onto neurons in the substantia nigra and retrorubral field which project to the medullary reticular formation

Anatomical tract-tracing and immunohistochemical techniques involving correlated light and electron microscopy were used to determine whether the descending striatal and pallidal afferents to the substantia nigra pars reticulata converge onto individual neurons projecting to the pontomedullary and medullary reticular formation in the rat. Injections of biocytin into the ventrolateral region of the striatum and Phaseolus vulgaris-leucoagglutinin into the ventrolateral and caudal regions of the globus pallidus led to overlapping anterogradely labelled terminal fields within the dorsolateral substantia nigra pars reticulata. These terminal fields were punctuated by neurons which had been retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into the lateral pontomedullary reticular formation. The anterogradely labelled striatal and pallidal terminals displayed different morphological characteristics; the striatal terminals were small and diffusely distributed throughout the neuropil without any particular neuronal association whereas the pallidal terminals were large and formed pericellular baskets around the perikarya of retrogradely and non-retrogradely labelled nigral neurons. In areas of the substantia nigra where there was an overlap between the two terminal fields, individual retrogradely labelled nigroreticular neurons were found to be apposed by both sets of anterogradely labelled terminals. Electron microscopic analysis revealed that the striatonigral and pallidonigral terminals displayed different ultrastructural features, the striatal terminals were small, contained few mitochondria and formed symmetric synaptic contacts predominantly with the distal dendrites of nigroreticular neurons whereas the pallidal terminals were large, contained numerous mitochondria and formed symmetric synaptic contacts preferentially with perikarya and proximal dendrites of nigroreticular neurons. Post-embedding immunohistochemical staining revealed that both striatonigral and pallidonigral terminals, some which formed synaptic contact with nigroreticular neurons, displayed GABA immunoreactivity. Examination of twelve retrogradely labelled neurons in the electron microscope revealed that all received synaptic inputs from both sets of anterogradely labelled terminals. In addition to the substantia nigra pars reticulata, neurons of the retrorubral field were also retrogradely labelled following injections of wheatgerm agglutinin conjugated to horseradish peroxidase into pontomedullary reticular formation. These retrorubroreticular neurons were part of a continuum of labelled cells which extended from the dorsolateral substantia nigra pars reticulata caudally into the retrorubral field. When combined with anterograde tracing methods it was found that the retrorubroreticular neurons received synaptic inputs from pallidal terminals which were morphologically similar to the pallidonigral terminals and formed symmetric synapses with the neuronal somata and proximal dendrites. In contrast to nigroreticular neurons, the stratonigral terminals were not seen in contact with retrorubroreticular cells.(ABSTRACT TRUNCATED AT 400 WORDS)

On the significance of subterritories in the "accumbens" part of the rat ventral striatum

Although many workers have appreciated the striking cytologic and neurochemical similarities of neostriatum, accumbens and olfactory tubercle, a compelling case for regarding these areas as territories in a striatal complex awaited the arguments made by Heimer and his colleagues based on their investigations of connections. A number of recent papers support this viewpoint and extend it with the characterization of three accumbal subterritories: core, shell and rostral pole. The case for separate classifications of systems traversing the accumbens has become more compelling with each study that demonstrates connectional, cytoarchitectural and neurochemical specificity conforming to the boundaries separating the core and its downstream targets from the shell and its projection fields. Furthermore, its apparent composite of core-like and shell-like characteristics distinguishes the rostral pole as yet another unique subterritory. Differences in compartmental organization distinguish the accumbens and neostriatum. The available data are consistent with the periventricular and rostrolateral enkephalin-rich zones being ventralmost parts of the neostriatal patch and matrix compartments, respectively. The accumbal cell cluster compartment, on the other hand, appears to be a separate entity, with connectional and neurochemical features that are dissimilar to both patch and matrix of neostriatum. Boundaries between the accumbens and caudate-putamen remain elusive, and the point of view that such boundaries do not exist but, rather, are represented by "transition zones" must to a large degree reflect the reality. Likewise, it is important to acknowledge that the boundaries between accumbal subterritories are not necessarily distinct or observed faithfully by all of the afferent systems. "Transition zones" appear to be particularly significant organizational features in rostral and lateral parts of the accumbens. Interestingly, histochemically distinct cell clusters tend to be numerous in boundary regions between adjacent territories and subterritories. The predominant organizational pattern appears to be one in which the core, shell and rostral pole engage different forebrain systems that possibly subserve entirely different functions mediated by distantly related mechanisms. In this regard, it is of paramount interest that the processing of information conveyed to the accumbens by diverse cortical and subcortical inputs occurs within distinct and perhaps very different dopaminergic environments in the core, shell and rostral pole (e.g., see Refs 24, 34, 90, 110).

The non-NMDA glutamate antagonist NBQX blocks the local hippocampal toxicity of kainic acid, but not the diffuse extrahippocampal damage

The neuronal lesion caused locally by the injection of 0.47 nmol kainic acid into the dorsal hippocampus was greatly reduced by the co-administration of 190 nmol 2,3-dihydro-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX). Protection was particularly marked for the neurons present in the CA3 and dentate hilar regions which are the neurons most vulnerable to kainic acid. On the other hand, systemic administration of NBQX (3 doses of 30 mg/kg i.p.) was completely ineffective in blocking neuronal loss in the CA3 and hilar regions. Furthermore, neither hippocampal nor systemic NBQX could prevent the diffuse neuronal damage to other regions in the limbic system outside of the dorsal hippocampus.

Somatotopic organization in rat striatum: evidence for a combinational map

2-Deoxy-D-[14C]glucose autoradiography was used in awake rats to map neural activity in the sensorimotor sector of striatum. Stimulation of hindlimb, trunk, or forelimb activated primary sensory cortex in a localized columnar pattern, indicating activation of somatosensory receptors and a discrete cortical functional unit. In sensorimotor striatum, an image analysis detection technique revealed regions of maximal activity, or features, that formed a patchy pattern of activation reminiscent of the known anatomic patterns of cortico-striate terminals. Ipsilateral as well as contralateral activation was observed. The activated areas revealed a body map in striatum that was organized in a manner consistent with cortical topography (dorsoventrally: hindlimb, trunk, forelimb) at most anteroposterior levels, similar to that found in other species. However, at other levels, a different organization (e.g., trunk, hindlimb, forelimb) was observed. Furthermore, the arrangements of body region and side were also unique at different anteroposterior levels. Thus, functional activity showed multiple, different juxtapositions of body elements--i.e., a combinational map. The data suggest that striatum may provide an anatomic substrate for different combinations of inputs necessary to select and integrate movement.

Cortical and quasi-cortical regions innervate ventrostriopallidal structures in the rat: an electrophysiological analysis

Antidromic unit driving was utilized to demonstrate afferent projections from prefrontal cortical (PFC) and quasi-cortical structures (main olfactory bulb, MOB; anterior olfactory nucleus, AON; basolateral amygdaloid nucleus, BLA) to the ventrostriopallidal region (VSPR) of the rat. In all regions explored, a substantial number of antidromically invaded neurons were found following electrical stimulation of the VSPR. In addition, both the AON and the amygdalostriatal zone harbor cells with branched axons which innervate the MOB and the VSPR and the agranular insular cortex and the VSPR, respectively. These results support and extend previous neuroanatomical and neurophysiological data on afferent connections of the VSPR and emphasize the fact that several regions of the basal forebrain, which are actively involved in processing of olfactory information, and the VSPR, are more closely interrelated than hitherto suspected.

Injections of the NMDA-antagonist D-2-amino-7-phosphonoheptanoic acid (AP-7) into the nucleus accumbens of rats enhance switching between cue-directed behaviours in a swimming test procedure

The present study explores the behavioural effects of intra-accumbens injections of D-2-amino-7-phosphonoheptanoic acid (AP-7), a selective competitive N-methyl-D-aspartate (NMDA) receptor antagonist, using a swimming test procedure, in which rats were forced to swim for 6 min. The behaviour of the rats was analysed in terms of cue-directed (CDBs) and non-cue-directed behaviours (NCDBs). AP-7 (100-500 ng/0.5 microliter) dose-dependently enhanced the number of switches to CDBs, without affecting the number of switches to NCDBs. Further analysis of the data showed that the number of switches between CDBs was enhanced, while no effect was found on the number of switches from NCDBs to CDBs, from CDBs to NCDBs or between NCDBs. These data suggest that the NMDA-receptor in the nucleus accumbens is involved in the ability to switch between cue-directed behaviours.

Topographical organization of the projections from physiologically identified areas of the motor cortex to the striatum in the rat

The present study was undertaken to determine in the rat the topography of the neostriatal projections originating from the motor cortex. For that purpose, anterograde tracers (Phaseolus vulgaris leucoagglutinin: PHA-L; wheat germ agglutinin conjugated to horseradish peroxidase: WGA-HRP) were deposited in discrete cortical sites physiologically identified by microstimulation. Five major motor areas were considered in this study: the rostral (RFL) and caudal (CFL) forelimb areas, the hindlimb (HL) area, the vibrissae motor-frontal eye field (V-FEF) region and the jaw, lips and tongue (JLT) area (according to the nomenclature of Neafsey et al.). The results indicate that functionally different regions of the motor cortex project to different sectors of the caudate putamen (CPU). All 3 distinct limb areas RFL, CFL and HL project to the dorsolateral quarter of the CPU, V-FEF area projects to the dorsomedial quarter, whereas the JLT area projects to the ventrolateral quarter. The pattern of terminal labeling is relatively consistent, whatever the cortical area in which the tracer is deposited. This pattern is characterized by the presence of two or more labeled bands which are obliquely oriented along a ventrolateral-dorsomedial axis. Control experiments were also undertaken in which a retrograde tracer (WGA-HRP) was deposited in various neostriatal loci. The results are congruent with the findings of the anterograde study and further indicate that a given neostriatal sector receives projections from cytoarchitectonically different but functionally related regions of the neocortex. The somatotopic features of both motor and somatosensory corticostriatal projections appear to be in register. In addition, the striatal distribution of motor cortical fibers was compared in 6 experimental cases to the compartmental subdivision of the striatum in patches and matrix, following immunohistochemical localization of calbindin 28 kDa. The calbindin-immunoreactivity is extremely weak in the dorsolateral sector but is higher in the central and ventrolateral parts of the CPU. In these deep striatal regions receiving fibers from V-FEF, JLT and, to a lesser extent, from the limb areas, the cortical fibers are mostly directed to the matrix. The band-like organization of the projection from the motor cortex is correlated to the patch-matrix organization. The patches correspond to the bands of low density of terminal fibers and the matrix to the bands of high terminal density. The present results provide an anatomical basis to both electrophysiological and behavioral observations suggesting that functional distinctions can be established between subregions of the striatum.

Effects of 6-hydroxydopamine lesions of the prefrontal cortex on tyrosine hydroxylase activity in mesolimbic and nigrostriatal dopamine systems

The effects of prefrontal cortical dopamine depletion on subcortical dopamine function in the rat were examined. 6-Hydroxydopamine lesions of the dopaminergic innervation of the prefrontal cortex did not alter concentrations of dopamine or its metabolite 3,4-dihydroxyphenylacetic acid in either the striatum or nucleus accumbens. Similarly, the activity of the catecholamine biosynthetic enzyme tyrosine hydroxylase in the striatal complex was not changed in animals with prefrontal cortical lesions. Animals sustaining neurotoxic lesions of the prefrontal cortex were challenged with haloperidol in order to activate submaximally tyrosine hydroxylase activity. The magnitude of the haloperidol-induced increase in enzyme activity in the nucleus accumbens was significantly greater in lesioned subjects than in control animals. These data suggest that lesions of the prefrontal cortical dopamine innervation do not result in significant alterations in basal dopaminergic function in the striatal complex. However, lesions of the dopaminergic innervation of the prefrontal cortex significantly increase the responsiveness of mesolimbic dopamine afferents to pharmacological challenge.

Distribution of neuronal cannabinoid receptor in the adult rat brain: a comparative receptor binding radioautography and in situ hybridization histochemistry

The neuronal distribution of cannabinoid receptor in the adult rat brain is reported, combining receptor binding radioautography using the synthetic psychoactive cannabinoid ligand CP55,940 with in situ hybridization histochemistry using oligonucleotide probes complementary to rat cannabinoid receptor cDNA. In the cerebral cortex, especially in the frontal and cingulate cortex, dense binding was found in layers I and VI together with slight mRNA levels in a majority of both pyramidal and non-pyramidal-shaped neurons and of high mRNA levels in a moderate number of non-pyramidal-shaped neurons especially in layers II-III and V-VI. In the hippocampal dentate gyrus, very dense staining was found in the molecular layer together with high mRNA levels in a moderate number of hilar neurons close to the granular layer. In Ammon's horn, especially in the CA3 sector, very dense binding was found in the dendritic layers together with slight mRNA levels in the majority of the pyramidal cells and high mRNA levels in a moderate number of interneurons. In the basal ganglia, binding was very dense in the lateral putamen, substantia nigra pars reticulata, globus pallidus and entopeduncular nucleus, moderate in the medial putamen and caudate; and slight in the accumbens, together with slight to moderate mRNA levels in the striatal medium-sized neurons. Together with slight binding, slight to moderate mRNA levels were found in the majority of the neurons in the subthalamic nucleus. No binding and mRNA were found in the substantia nigra pars compacta and ventral tegmental area. Slight to moderate binding was found together with slight to moderate mRNA levels in the majority of neurons in the anterior olfactory nucleus; septum, especially medial septum and diagonal band of Broca; amygdala, especially basolateral amygdala; lateral habenula; ventromedial hypothalamic nucleus; lateral interpeduncular nucleus; central gray, dorsal cochlear nucleus; parabrachial nucleus; dorsal pontine tegmentum; pontine nuclei; commissural part of the nucleus tractus solitarius; inferior olive and dorsal horn of the spinal cord. In the cerebellum, very dense binding was found in the molecular layer together with slight mRNA levels in the majority of the granule cells and moderate mRNA levels in the basket and stellate cells. In conclusion, this study provides, for the first time, indirect assessment of the neurons containing cannabinoid receptor in the entire adult rat brain and will serve as a basis for future direct morphological confirmation using receptor immunohistochemistry and for functional studies.

Behaviourally derived estimates of excitability in striatal and medial prefrontal cortical self-stimulation sites

The refractory periods of the substrate underlying brain-stimulation reward were investigated in three rats with moveable electrodes implanted in the rostral caudate-putamen and the medial prefrontal cortex. Acquisition of caudate-putamen self-stimulation occurred within the first session, while self-stimulation for medial prefrontal cortex was observed only after three sessions of caudate-putamen stimulation. The currents required for self-stimulation ranged from 300 to 800 microA (0.1 ms pulse duration) across animals; the maximum response rates averaged roughly 40 bar presses per minute for both structures. Refractory period estimates were obtained from ten caudate-putamen and four medial prefrontal cortex sites. The time course of recovery had the following profile: the curves began to rise at 0.65 ms and 0.95 ms for caudate-putamen and medial prefrontal cortex stimulation, respectively, thereafter increasing to approach an asymptote at 6.00 ms for the caudate-putamen and 6.25 ms for the medial prefrontal cortex. The mean effectiveness value corresponding to the asymptotic portion of the curves was 73% for the caudate-putamen and 69% for the medial prefrontal cortex. Like other forebrain structures, the behaviourally derived refractory periods underlying caudate-putamen and medial prefrontal cortex stimulation, at least at these particular sites, are significantly longer than those observed in most medial forebrain bundle areas, both beginning and ending later. One interpretation for the similarity in their refractory period profiles and the apparent facilitating effect of caudate-putamen stimulation on acquisition of medial prefrontal cortex self-stimulation is that these two regions form part of the same reward substrate.

Effects of anaesthetics, anticonvulsants and glutamate antagonists on kainic acid-induced local and distal neuronal loss

A semi-quantitative estimation has been made of the effect of anaesthetics, anticonvulsants and glutamate antagonists on the extent of neuronal loss in the hippocampus caused by the local injection of the excitotoxin kainic acid, and on the vulnerability of neurons in various extrahippocampal regions due to the resulting seizure activity. Following the intrahippocampal injection of 0.47 nmol kainic acid (a submaximal dose), the amount of neuronal loss in the dorsal hippocampus was greater when given under the short-acting anaesthetics halothane and ketamine (a non-competitive glutamate antagonist), than when given under pentobarbital anaesthesia (with or without co-administration of ketamine (30 mg/kg)). When kainic acid was injected under halothane or ketamine anaesthesia a greater number of extrahippocampal limbic regions (distal toxicity) were also affected, usually on the ipsilateral side, and the extent of damage in each of these regions was generally more extensive. The anticonvulsants MK 801 and diazepam, or multiple injections of ketamine over a period of 5 h, decreased both the local and distal toxicity of kainic acid injected under short duration anaesthesia, to levels similar to those found under pentobarbital anaesthesia. However, these compounds, even at high doses, could not reliably prevent all seizure-related damage in extrahippocampal areas.

Do forebrain structures compete for behavioral expression? Evidence from amphetamine-induced behavior, microdialysis, and caudate-accumbens lesions in medial frontal cortex damaged rats

The neurochemical basis of behavioral changes following medial frontal cortex damage were investigated. Experiment 1 examined locomotion in response to D-amphetamine (1.5 and 5 mg/kg) in rats that had received bilateral aspirative lesions of the medial frontal cortex alone or in combination with 6-hydroxydopamine (6-OHDA) lesions of the nucleus accumbens or caudate-putamen. Relative to controls, medial frontal cortex rats were initially hypoactive (day 1 postoperative) but rapidly became hyperactive (days 5-15 postoperative). Locomotor-time profiles and stereotypy ratings showed that amphetamine produced a selective enhancement of locomotion at the expense of stereotyped behavior. Nucleus accumbens lesions blocked the locomotion but enhanced stereotyped behavior in the medial frontal cortex damaged rats, suggesting that amphetamine-enhanced locomotion is dependent upon the integrity of the nucleus accumbens. In Experiment 2, intracerebral microdialysis was used to examine whether alterations in dopamine (DA) or monoamine metabolites in the nucleus accumbens or caudate-putamen accompanied the lesion-induced changes in locomotion. There were no differences in extracellular DA or monoamine levels between control rats and medial frontal cortex rats when tested on day 1 or day 15 postsurgery, either when they were at rest, while they walked on a motor-driven belt, or after amphetamine treatment. Therefore, it seems unlikely that changes in amphetamine-induced locomotion following medial frontal cortex lesions are related to underlying modifications in dopaminergic activity in the nucleus accumbens. It is suggested that neural structures compete for behavioral expression and that postlesion behavioral alterations reveal the competitive advantage of remaining intact neural systems.

Topographical organization and relationship with ventral striatal compartments of prefrontal corticostriatal projections in the rat

The anterograde tracer Phaseolus vulgaris-leucoagglutinin was used to examine the topographical organization of the projections to the striatum arising from the various cytoarchitectonic subdivisions of the prefrontal cortex in the rat. The relationship of the prefrontal cortical fibres with the compartmental organization of the ventral striatum was assessed by combining PHA-L tracing and enkephalin-immunohistochemistry. The prefrontal cortex projects bilaterally with an ipsilateral predominance to the striatum, sparing only the lateral part of the caudate-putamen complex. Each of the cytoarchitectonic subfields of the prefrontal cortex has a longitudinally oriented striatal terminal field that overlaps slightly with those of adjacent prefrontal areas. The projections of the medial subdivision of the prefrontal cortex distribute to rostral and medial parts of the striatum, whereas the lateral prefrontal subdivision projects to more caudal and lateral striatal areas. The terminal fields of the orbital prefrontal areas involve midventral and ventromedial parts of the caudate-putamen complex. The projection of the ventral orbital area overlaps with that of the prelimbic area in the ventromedial part of the caudate-putamen. In the "shell" region of the nucleus accumbens, fibres arising from the prelimbic area concentrate in areas of high cell density that are weakly enkephalin-immunoreactive, whereas fibres from the infralimbic area avoid such areas. Rostrolaterally in the "core" region of the nucleus accumbens, fibres from deep layer V and layer VI of the dorsal part of the prelimbic area avoid the enkephalin-positive areas surrounding the anterior commissure and distribute in an inhomogeneous way over the intervening moderately enkephalin-immunoreactive compartment. The other prefrontal afferents show only a preference for, but are not restricted to, the latter compartment. In the border region between the nucleus accumbens and the ventromedial part of the caudate-putamen complex, patches of strong enkephalin immunoreactivity receive prefrontal cortical input from deep layer V and layer VI, whereas fibres from more superficial cortical layers project to the surrounding matrix. Individual cytoarchitectonic subfields of the prefrontal cortex thus have circumscribed terminal domains in the striatum. In combination with data on the organization of the midline and intralaminar thalamostriatal and thalamoprefrontal projections, the present results establish that the projections of the prefrontal cortical subfields converge in the striatum with those of their midline and intralaminar afferent nuclei. The present findings further demonstrate that the relationship of the prefrontal corticostriatal fibres with the neurochemical compartments of the ventral striatum can be influenced by both the areal and the laminar origin of the cortical afferents, depending on the particular ventral striatal region under consideration.

Projections from the nucleus accumbens to cholinergic neurons of the ventral pallidum: a correlated light and electron microscopic double-immunolabeling study in rat

A correlated light- and electron microscopic double-immunolabeling study combining choline acetyltransferase immunocytochemistry with anterograde tracing of Phaseolus vulgaris leucoagglutinin (PHA-L) revealed that axons of the nucleus accumbens terminate on cholinergic neurons of the ventral pallidum. These findings are discussed with respect to the possibility that these cholinergic neurons may be part of parallel circuits, providing feedback to the same cortical and amygdaloid areas which innervate the nucleus accumbens.

Glutamate stimulation of tyrosine hydroxylase is mediated by NMDA receptors in the rat striatum

We have studied the action of glutamate on striatal tyrosine hydroxylase activity and determined which type of glutamate receptors are involved. Glutamate stimulated (EC50 = 4 +/- 2 microM) the activity of tyrosine hydroxylase in slices of rat neostriatum. The selective N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (10 microM) blocked the stimulation; however, both the non-NMDA receptor antagonist glutamate diethyl ester (10 microM) and the general excitatory amino acid antagonist kynurenate (10 microM) had no effect. NMDA was even more potent than glutamate in stimulating tyrosine hydroxylase activity. Quisqualate (100 microM) only slightly stimulated the enzyme, and kainate had practically no effect. Omission of Mg2+ from the incubation medium potentiated the glutamate stimulation. Neither tetrodotoxin nor atropine prevented the stimulation. These results suggest that glutamate stimulates striatal tyrosine hydroxylase activity via NMDA receptors. The lack of effect of tetrodotoxin and atropine suggests that glutamate acts on NMDA receptors located on the dopaminergic nigrostriatal terminal. The stimulation may involve the entry of Ca2+ into the terminal through the NMDA receptor ionophore, since a Ca(2+)-free medium or cadmium totally blocked the stimulation of the enzyme by glutamate.

Cellular interactions in the striatum involving neuronal systems using ?classical? neurotransmitters: Possible functional implications

The neostriatum contains a wide variety of neuroactive substances associated with several well-defined functional neuronal systems. This structure, which is the seat of numerous neurological pathological disorders, is commonly used as a model for studying the basic mechanisms of neurotransmitter interactions in the brain and their putative involvement in striatal functions. Increasing interest has been focusing lately on the cellular interactions that may occur between the corticostriatal putatively glutamatergic system and the nigrostriatal dopaminergic input. Current evidence suggests that the activatory corticostriatal glutamatergic input may play a more crucial role in regulating striatal functions than was formerly assumed in comparison with the dopaminergic input. The key role of cholinergic interneurons in the striatum may therefore be attributable to the fact that they modulate the glutamatergic transmission to GABA striatal efferent neurons. Likewise, dopamine may actually act indirectly in the striatum by "tuning down" the cortical excitation of striatal neurons. Consequently, an impairment of the dopaminergic transmission such as that occurring in Parkinsonism may lead to an increase in the corticostriatal glutamatergic transmission, which may further contribute towards reinforcing the "imbalance" between subsets of striatal neuronal systems controlling the output of the basal ganglia.

Effect of haloperidol and clozapine on the density of "perforated" synapses in caudate, nucleus accumbens, and medial prefrontal cortex

Perforated synapses, which contain a discontinuous density along the postsynaptic membrane, can increase or decrease in numbers following various behavioral and biochemical manipulations. We have previously established that 14-day treatment with haloperidol causes an increase in the number of perforated synapses within the caudate nucleus (dorsolateral region) but not the nucleus accumbens (Meshul and Casey 1989). This effect was reversed if the animals were withdrawn from the drug for an equivalent period of time. We have now further examined the effects of haloperidol administration, which is associated with a high incidence of extrapyramidal side effects (EPS) and tardive dyskinesia (TD), and assessed the effects of clozapine, which appears to have a lower potential for inducing EPS and TD. Administration of haloperidol for 2 weeks significantly increased the percentage of perforated synapses in the caudate, but not in the nucleus accumbens or layer VI of medial prefrontal cortex (MPCx). There was an increase in specific [125I]epidepride binding to D-2 receptors in the caudate nucleus and MPCx following haloperidol. Administration of clozapine for 2 weeks did not affect the percentage of perforated synapses in any of the three dopamine (DA)-rich regions that were examined. There was an increase in specific [3H]SCH 23390 binding to D-1 receptors and in specific [125I]epidepride binding to D-2 receptors only within MPCx following clozapine.(ABSTRACT TRUNCATED AT 250 WORDS)

The regulation of subcortical dopamine systems by the prefrontal cortex: interactions of central dopamine systems and the pathogenesis of schizophrenia

A recent hypothesis of the pathogenesis of schizophrenia posits a developmentally-specific dysfunction of the dopaminergic innervation of the prefrontal cortex (PFC; Weinberger, 1987; Berman and Weinberger, 1990). It has been difficult to reconcile this hypothesis with the observation that all clinically effective antipsychotic drugs used for the treatment of schizophrenia block dopamine D2 receptors (see Deutch et al., 1991a). A resolution between the suggestion of functional dopamine (DA) "depletion" in the PFC and enhanced subcortical DA function was offered by studies of Carter, Pycock, and associates (Carter and Pycock, 1980; Pycock et al., 1980a, b). These investigators reported that depletion of DA in the rat PFC enhanced DA utilization in subcortical sites such as the nucleus accumbens septi (NAS) and striatum. Thus, a functional deficit in DA neurotransmission in the PFC would increase subcortical DA turnover, and the D2 receptor blockade induced by antipsychotic drugs would counteract the increase in dopaminergic tone in subcortical sites. This hypothesis has been particularly influential because it incorporates both an explanation for negative symptoms, which are thought to reflect cortical dysfunction (a derangement in DA transmission in the PFC), and the efficacy of antipsychotic drugs in the treatment of positive symptoms (arising from increases in subcortical DA tone). As attractive as this hypothesis has been, the physiological underpinnings that subserve such system interactions have remained elusive. Pycock, Carter, and colleagues (Carter and Pycock, 1980; Pycock et al., 1980a, b) reported that 6-hydroxydopamine (6-OHDA) lesions of the PFC increase DA levels and DA turnover in the striatum; certain aspects of their findings have been confirmed (Martin-Iversen et al., 1986; Leccese and Lyness, 1987; Haroutounian et al., 1988). However, other groups have been unable to confirm either the biochemical or behavioral findings of Pycock and associates (Joyce et al., 1983; Oades et al., 1986; Deutch et al., 1990). Moreover, Pycock and colleagues did not observe consistent effects of PFC DA deafferentation on various indices of subcortical DA function (Carter and Pycock, 1980; Pycock et al., 1980a, b). In light of the importance that such DA system interactions may have in the pathogenesis of schizophrenia, we have reinvestigated the effects of cortical DA lesions on subcortical DA function.

Excitatory amino acid binding sites in the basal ganglia of the rat: a quantitative autoradiographic study

Quantitative receptor autoradiography was used to determine the distribution of excitatory amino acid binding sites in the basal ganglia of rat brain. alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid, N-methyl-D-aspartate, kainate, quisqualate-sensitive metabotropic and non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had their highest density in striatum, nucleus accumbens, and olfactory tubercle. Kainate binding was higher in the lateral striatum but there was no medial-lateral striatal gradient for other binding sites. N-Methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding sites were most dense in the nucleus accumbens and olfactory tubercle. There was no dorsal-ventral gradient within the striatal complex for the other binding sites. Other regions of the basal ganglia had lower densities of ligand binding. To compare binding site density within non-striatal regions, binding for each ligand was normalized to the striatal binding density. When compared to the striatal complex, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and metabotropic binding sites had higher relative density in the globus pallidus, ventral pallidum, and subthalamic nucleus than other binding sites. Metabotropic binding also had a high relative density in the substantia nigra. Non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had a high relative density in globus pallidus, ventral pallidum, and substantia nigra. N-Methyl-D-aspartate binding sites had a low relative density in pallidum, subthalamic nucleus, substantia nigra and ventral tegmental area. Our data indicate heterogeneous distribution of excitatory amino acid binding sites within rat basal ganglia and suggest that the character of excitatory amino acid-mediated neurotransmission within the basal ganglia is also heterogeneous.

Membrane properties and synaptic responses of rat striatal neurones in vitro

1. A tissue slice containing a section of striatum was cut obliquely from rat brain so as to preserve adjacent cortex and pallidum. Intracellular recordings were made from 368 neurones, using either conventional or tight-seal configurations. 2. Two types of neurone were distinguished electrophysiologically. Principal cells (96%) had very negative resting potentials (-89 mV) and a low input resistance at the resting membrane potential (39 M omega): membrane conductance (10 nS at -65 mV) increased within tens of milliseconds after the onset of hyperpolarization (99 nS at -120 mV). Secondary cells (4%) had less negative resting potentials (-60 mV) and a higher input resistance (117 m omega at the resting potential): hyperpolarization caused an inward current to develop over hundreds of milliseconds that had the properties of H-current. 3. Most principal cells were activated antidromically by electrical stimulation of the globus pallidus or internal capsule. Intracellular labelling with biocytin showed that principal cells had a medium sized soma (10-18 microns), extensive dendritic trees densely studded with spines and, in some cases, a main axon which extended towards the globus pallidus. 4. Electrical stimulation of the corpus callosum or external capsule evoked a depolarizing postsynaptic potential. This synaptic potential was reversibly blocked by a combination of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and DL-2-amino-5-phosphonovaleric acid (APV, 30 microM), but was unaffected by bicuculline (30 microM) and picrotoxin (100 microM). The underlying synaptic current had a fast component (time to peak about 4 ms), the amplitude of which was linearly related to membrane potential and which was blocked by CNQX; in CNQX the synaptic current had a slower component (time to peak about 10 ms) which showed voltage dependence typical of N-methyl-D-aspartate (NMDA) receptors. Both currents reversed at -5 mV. 5. Focal electrical stimulation within the striatum (100-300 microns from the site of intracellular recording) evoked a synaptic potential that was partially blocked (45-95%) by CNQX and APV: the remaining synaptic potential was blocked by bicuculline (30 microM). The bicuculline-sensitive synaptic current reversed at the chloride equilibrium potential. 6. The findings confirm that the majority of neostriatal neurones (principal cells, medium spiny neurones) project to the pallidum and receive synaptic inputs from cerebral cortex mediated by an excitatory amino acid acting through NMDA and non-NMDA receptors. These cells also receive synaptic inputs from intrinsic striatal neurones mediated by GABA.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional changes of striatal dopamine receptors following denervation by 6-hydroxydopamine and fetal mesencephalic grafts in the rat

Young adult female rats received a 6-hydroxydopamine lesion in the left substantia nigra and, 3 weeks later, some of them were grafted with a cell suspension from the ventral mesencephalon of rat embryos (14-15 days old). Six months after transplantation, some grafted rats, following injection of amphetamine, had switched to turning only toward the intact side (type 1), whereas others turned toward the intact side only during the first half of the test (type 2). Levels of dopamine, dihydroxyphenylacetic acid and homovanillic acid were, respectively, 2%, 15% and 35% of the intact side in the denervated striatum of 6-hydroxydopamine rats. Dopamine concentrations were restored to 13% and 10% of the intact side in the grafted striatum of type 1 and type 2 animals, respectively. Levels of homovanillic acid were unchanged following grafts whereas those of dihydroxyphenylacetic acid increased by 209% and 247% in the grafted striatum of type 1 and type 2 animals, respectively. The ratios of dihydroxyphenylacetic acid/dopamine as well as homovanillic acid/dopamine were low in the intact striatum whereas they increased in the denervated striatum with or without graft. The tyrosine hydroxylase immunoreactivity decreased by about 80% in the denervated striatum of 6-hydroxydopamine rats. In type 1 rats, tyrosine hydroxylase immunoreactivity revealed that the graft was localized in the dorsomedial part of the denervated striatum, whereas in type 2 animals, it was also in the medial striatum but it overlapped the dorsal and ventral parts of it equally. D1 as well as D2 dopamine receptors were measured throughout the striatum (9.0-7.6 rostral-caudal coordinates), by autoradiography, using [3H]SCH 23390 (D1 antagonist) and [3H]spiperone (D2 antagonist) binding. Supersensitive D2 receptors were normalized in the dorso- and ventromedial parts of the grafted striatum. D2 receptor density was higher in type 2 than in type 1 rats, more specifically at 8.6-8.2 rostral-caudal coordinates, where the graft was. D1 receptor supersensitivity was modest compared to D2 receptors in the striatum of 6-hydroxydopamine rats and decreased following grafts. DA receptors changes in the striatum, following fetal mesencephalic grafts, may explain the behavioral recovery seen in grafted rats.

Representation of the body by single neurons in the dorsolateral striatum of the awake, unrestrained rat

Single cell recordings in awake monkeys and cats have demonstrated that individual body parts are represented within striatal subregions receiving projections from somatic sensorimotor cortex. Literature indicating that the lateral striatum of the rat receives similar cortical inputs and subserves sensorimotor functions prompted a study of whether this subregion contains similar representations of the body. Single cell recordings were obtained from 923 neurons of 24 awake, unrestrained rats. Of 788 neurons categorized according to body part, 264 (34%) discharged in relation to active movement, passive manipulation, and/or cutaneous stimulation of a particular part of the body; the remainder were related to global, whole body movement (38%) or were unresponsive (28%). Neurons related to individual body parts were recorded throughout the entire anterior-posterior extent of the dorsolateral striatum (+1.60 to -2.12 mm A-P, from bregma), intermingled among each other in all 3 dimensions. Two topographic arrangements were observed. First, neurons that fired rhythmically, in phase with low frequency (5-6 Hz) whisking of the vibrissae were segregated in the caudal striatum (-0.2 to -2.12 mm A-P) from neurons related to other body parts, which were distributed from +1.6 to -0.8 mm A-P. Second, representations of the head and face were located ventral to those of the limbs, despite substantial overlap in their overall distributions. A prominent feature of individual electrode tracks was the clustering together of cells related to the same body part. Neurons related to body parts exhibited substantial diversity, which took several distinct forms. Some neurons fired during movement or sensory stimulation in any direction, whereas others showed selectivity for a particular direction. Certain neurons responded to sensory stimulation of a large unilateral region of the body (e.g., all vibrissae or the entire forelimb), whereas others responded to stimulation of highly restricted regions (e.g., a single vibrissa or a single forepaw digit). Finally, neurons differed in the extent to which they exhibited active and passive properties. Among vibrissae-related neurons, one group fired rhythmically during whisking but did not respond to sensory stimulation of the vibrissae; a second group responded to sensory stimulation of the vibrissae but did not fire rhythmically during whisking; a third group showed both properties. Among limb-related neurons, firing during active movement was a property of every cell; none showed sensory responsiveness without showing a relation to active movement of one limb. Of the limb-related neurons, 89% tested responded to passive manipulation of the limb to which the neuron was actively related, and 71% also responded to cutaneous stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Localized intracaudate dopamine D2 receptor activation during the post-training period improves memory for visual or olfactory conditioned emotional responses in rats

Rats with cannulas aimed at the posteroventral (PV) or ventrolateral (VL) areas of the caudate nucleus were trained on a conditioned emotional response (CER) task. Post-training microinjections of the indirect catecholamine agonist, d-amphetamine (5 micrograms), or of the dopamine D2 receptor agonist, LY171555 (1 microgram), into the PV area improved retention of a CER with a visual CS, but had no effect on a CER with an olfactory CS. Post-training injections of the same two drugs into the VL area improved retention of a CER with an olfactory CS, but had no effect on a CER with a visual CS. Post-training injections of the dopamine D1 receptor agonist, SKF38393 (0.5, 1.0, 2.0 micrograms), into either site had no effects on either CER. These findings suggest that different areas of the caudate nucleus mediate acquisition of CERs with different CSs, possibly implicating the topographically organized corticostriatal innervation in the acquisition of certain types of memories in the caudate nucleus. The findings also suggest that dopamine D2 receptors in the caudate nucleus are involved in the acquisition of these CERs.

The effects of 6-OHDA-induced dopamine depletions in the ventral or dorsal striatum on maternal and sexual behavior in the female rat

The effects of dopamine-depleting 6-OHDA infusions in the ventral or dorsal striatum on maternal and sexual behaviors were examined in female rats. Like sham-operated controls, lactating rats receiving 6-OHDA in the ventral striatum built good nests, nursed the infants and showed maternal aggression toward strange intruders. By contrast, the lesioned females performed poorly in tests for pup retrieval, as reflected in greatly protracted retrieval latencies. There was no effect of ventral striatal DA depletions on proceptive and receptive elements of female sexual behavior, which was studied after lactation following ovariectomy and exogenous administration of ovarian hormones, but these animals did show an attenuated hyperactivity response to a low dose of amphetamine. Females with dopamine lesions in the dorsal striatum did not differ from controls with respect to maternal and sexual behavior, but they did show an enhanced hyperactivity response to amphetamine treatment.