Lateralized changes in behavior and striatal dopamine release following unilateral tactile stimulation of the perioral region: a microdialysis study

Whisker dependent responsiveness of C57BL/6J mice to different behavioral test paradigms

Whisker trimming is very common in C57BL/6J mice. Dewhiskering may lead to an alteration in the thalamocortical connectivity and relevant behavioral functions. Since C57BL/6J is a commonly used strain for neurobehavioral studies, it is important to examine how whisker dependent heterogeneity affects the internal validity of behavioral phenotypes. The present study aimed to investigate the responsiveness of mice to different behavioral test paradigms in the presence or absence of whiskers. We employed two models of whisker deprivation: Acute Whisker Desensitization (AWD) and Chronic Habitual Dewhiskering (CHD). The AWD model blocks whisker sensation by lidocaine application. For CHD model, mice at the age of 12 weeks were carefully scrutinized for presence or absence of whiskers and divided into three groups, the whiskered mice, partially dewhiskered mice and completely dewhiskered mice. The whisker-dependent behavioral functions were assessed using open field test, novel object recognition test, marble burying test and forced swim test. Our results showed that habitual dewhiskering significantly altered the short-term memory and basal anxiety-like functions. Such behavioral alteration due to dewhiskering was significantly different in fully and partially dewhiskered mice, which is indicative of behavioral adaptation to the whisker desensitization. Contrary to CHD, the Acute Whisker Desensitization ameliorated behavioral compulsivity and basal anxiety. Our results suggest that vibrissal desensitization in the mice may lead to changes in their affective and cognitive state. Since, heterogeneity in whisker status may affect behavioral functions, careful inspection of the whisker status of C57BL/6J mice is recommended to increase the reproducibility and reliability of results obtained from behavioral assessments.

Serotonin release in the central nucleus of the amygdala in response to noxious and innocuous cutaneous stimulation in anesthetized rats

We investigated the effect of noxious (pinching) and innocuous (stroking) stimulation of skin on serotonin (5-HT) release in the central nucleus of the amygdala (CeA) in anesthetized rats. 5-HT in the CeA was collected by microdialysis methods. Dialysate output from consecutive 10-min periods was injected into a high-performance liquid chromatograph and 5-HT was measured with an electrochemical detector. Bilateral pinching of the back for 10 min increased 5-HT release significantly; 5-HT release was also increased with stimulation of the forelimb or hindlimb. In contrast, stroking of these areas decreased 5-HT release significantly. Furthermore, simultaneous stroking and pinching produced no change in the 5-HT release. In conclusion, the present study demonstrates that 5-HT release in the CeA is regulated by somatic afferent stimulation in a modality-dependent manner, and that innocuous stimulation can dampen the change in 5-HT release that occurs in response to noxious stimulation.

Dopaminergic lateralisation in the forebrain: relations to behavioural asymmetries and anxiety in male Wistar rats

Neurochemical lateralisation has been demonstrated in dopaminergic systems in the rat brain, and it has been suggested that such lateralisation might contribute to asymmetric and emotional behaviour. Here, we investigated dopaminergic brain lateralisation in relation to spontaneous and drug-induced behavioural asymmetries, and to emotional behaviour in a sample of 24 male Wistar rats. Asymmetric behaviour was measured in the open field in the undrugged state and after a systemic challenge with the muscarinic receptor antagonist scopolamine (0.5 mg/kg). Emotional behaviour was measured in the elevated plus-maze. Dopaminergic lateralisation was assessed by means of a post-mortem analysis of tissue dopamine (DA) and dihydroxyphenyl acetic acid (DOPAC) content. We found higher DOPAC/DA ratios in the neostriatum, ventral striatum, frontal cortex and amygdala of the right hemisphere. In the open field, the complete sample of rats did not show a left/right asymmetry in spontaneous behaviour, whereas systemic scopolamine induced a left-sided preference in thigmotactic scanning. A correlational analysis yielded individual relationships between behaviour and post-mortem neurochemistry, since lateralisation of DOPAC/DA ratios in favour of the right ventral striatum was related to right-side thigmotaxis. Furthermore, a right dopaminergic lateralisation in the frontal cortex was associated with lower anxiety. The study indicates that asymmetries in ventral striatal dopamine might contribute to side preferences in thigmotactic scanning while frontal dopaminergic lateralisation might influence emotional processing.

Occlusal disharmonies modulate central catecholaminergic activity in the rat

Occlusal disharmonies have classically been thought to be involved in the etiopathogenesis of bruxism, as have, more recently, alterations in central neurotransmission, particularly dopaminergic neurotransmission. However, the connection between these two factors has still not been established. In this study, we assessed the effects of diverse occlusal disharmonies, maintained for either 1 day or 14 days, on neurochemical indices of dopaminergic and noradrenergic activity in the striatum, frontal cortex, and hypothalamus of the rat. The in vivo activity of tyrosine hydroxylase, determined as the accumulation of 3,4-dihydroxyphenylalanine (DOPA), 30 min after the administration of 3-hydroxybenzylhydrazine, a DOPA decarboxylase inhibitor, and dopamine and noradrenaline contents were quantified by high-performance liquid chromatography with electrochemical detection. The wearing of an acrylic cap on both lower incisors for 1 day induced a significant increase in DOPA accumulation in the regions analyzed, with parallel increases in dopamine levels in the hypothalamus and dopamine and noradrenaline in the frontal cortex. After the cap was maintained for 14 days, DOPA accumulation tended to return to control values, except in the left striatum, thereby causing an imbalance between hemispheres. In contrast, 1 or 14 days after the lower left and the upper right incisors were cut, less pronounced changes in catecholaminergic neurotransmission were found in the brain areas studied. Moreover, the cutting of one lower incisor did not modify either DOPA accumulation or dopamine and noradrenaline contents in the striatum or hypothalamus. These results provide experimental evidence of a modulation of central catecholaminergic neurotransmission by occlusal disharmonies, being dependent on the nature of the incisal alteration and on the time during which it was maintained.

Maternal motivation of lactating rats is disrupted by low dosages of haloperidol

Motorically-active maternal behaviors of rats, such as retrieval and licking of pups, are known to be reduced or suspended following systemic injection of > or = 0.2 mg/kg haloperidol (HAL), a dopamine (DA) receptor blocker. Further, when these behaviors are thwarted by muzzling, dams persistently attempt to make snout contact with pups by pushing them with the muzzle, indicative of intense maternal motivation. To evaluate whether time spent contact-seeking by muzzle-pushing is impaired by dosages of HAL too low to reduce retrieval and licking of pups, dams were fitted with a full muzzle (FM), given 0, 0.05 or 0.10 mg/kg HAL, and reunited with their pups for 30 min after a 4-h separation. Similarly-treated dams fitted with a control muzzle, which allows perioral contact with pups, displayed essentially normal maternal behavior. In FM dams, low dosages of HAL severely and dose-dependently reduced muzzle-pushing, as well as actual contact by handling-touching and moving pups with their paws, although the latency to initiate these behaviors by responders was not impaired. A threshold level of DA is apparently necessary for efficient motor control (handling) and for maternal incentive, persistent effort to achieve contact with pups (muzzle-pushing), consistent with an arousal explanation of the action of DA.

Anesthetics eliminate somatosensory-evoked discharges of neurons in the somatotopically organized sensorimotor striatum of the rat

The somatotopic organization of the lateral striatum has been demonstrated by anatomical studies of corticostriatal projections from somatosensory and motor cortices and by single-cell recordings in awake animals. The functional organization in the rat, characterized thus far in the freely moving rat preparation, could be mapped more precisely if a stereotaxic, and possibly an anesthetized, preparation could be used. Because striatal discharges evoked by innocuous somatosensory stimulation are used in mapping, this study tested whether such discharges can be observed during anesthesia, encouraged by responsiveness during anesthesia in somatosensory cortical layers projecting to the striatum. Electrode tracks through lateral striatum of anesthetized rats (pentobarbital or ketamine) revealed spontaneously discharging neurons but no discharges evoked by somatosensory examination (passive manipulation and cutaneous stimulation of 14 body parts). Similar tracks in chronically implanted rats showed evoked firing at numerous sites during wakefulness but not during anesthesia (pentobarbital or urethane). Comparisons of the activity of individual neurons between wakefulness and anesthesia showed that pentobarbital, ketamine, chloral hydrate, urethane, or metofane eliminated evoked firing and suppressed spontaneous firing. Recovery time was greater for neural than for behavioral measures. Thus, mapping as proposed is ruled out, and more importantly, the data show that somatotopically organized lateral striatal neurons stop discharging in response to natural stimulation during anesthesia. Available data indicate they do not reach threshold in response to depolarizations produced by glutamatergic corticostriatal synaptic transmission projected from the somatosensory cortex. These data and demonstrations of anesthetic-induced imbalances in most striatal neurotransmitters emphasize that many results regarding striatal physiology and pharmacology during anesthesia cannot be extrapolated to behavioral conditions, thus indicating the need for more empirical testing in conscious animals.

Effects of dopaminergic drugs, occlusal disharmonies, and chronic stress on non-functional masticatory activity in the rat, assessed by incisal attrition

Observational methods and the recording of nonspecific jaw movements or masticatory muscle activity have been used to evaluate oral parafunctional movements in animal models of bruxism. In this study, we have used a new approach in which the non-functional masticatory activity in the rat was assessed by the measurement of incisal attrition, with the aim of investigating the role of diverse factors involved in the etiology of bruxism. We quantified the attrition rate weekly by making superficial notches in the lower incisors and measuring the distances to the incisor edges. Repeated stimulation of the dopaminergic system with apomorphine led to an enhancement of the non-functional masticatory activity (p < 0.0001). The severity of the apomorphine-induced oral behavior was positively correlated (r(s) = 0.69, p < 0.01) with an increase in the incisal attrition rate (20.9%, p < 0.0001). Apomorphine-induced non-functional masticatory activity was strongly enhanced by the placement of an acrylic cap on both lower incisors (306%, p < 0.0001), but not by the cutting of a lower incisor. Repeated cocaine administration also increased the attrition rate (22.5%, p < 0.0001). However, neither chronic blockade of dopaminergic receptors with haloperidol, nor its withdrawal, modified attrition. In addition, since emotional disturbances are considered to be causal factors of bruxism, we tested whether experimental stress might accelerate tooth wear. Exposure to two different chronic stress regimes did not induce significant changes in incisal attrition. Moreover, exposure to chronic stress after the withdrawal of chronic haloperidol treatment did not alter attrition either. These results partially support the role of the central dopaminergic system in bruxism and suggest that stress, in general, may not be a relevant factor in tooth wear.

Increased neostriatal dopamine activity after intraperitoneal or intranasal administration of L-DOPA: on the role of benserazide pretreatment

L-DOPA provides the most potent medication to treat Parkinson's disease, and such systemic treatment is usually combined with a peripheral amino acid decarboxylase inhibitor to amplify its central effectiveness. Since L-DOPA can lose its efficacy or can lead to adverse effects with prolonged application, current pharmacokinetic and dynamic research is aimed at improving the drug's applicability. In a previous study, performed with in vivo microdialysis in the anesthetized rat, we have shown that intranasal L-DOPA administration (without prior decarboxylase inhibition) can increase extracellular dopamine levels in the neostriatum. Using similar experimental conditions in the present experiment, we tested the neurochemical effects of L-DOPA treatment in combination with the peripheral amino acid decarboxylase inhibitor benserazide. In accordance with other data, it was found that the combination of i.p. benserazide and i.p. L-DOPA led to pronounced increases of extracellular levels of dopamine, dihydroxyplenylacetic acid and homovanillic acid in the neostriatum, whereas i.p. L-DOPA alone only moderately increased dopamine, but strongly increased the metabolite levels. Furthermore, increased dopamine levels, and weaker increases of dihydroxyplenylacetic acid and homovanillic acid were observed after i.p. benserazide followed by intranasal L-DOPA. Finally, we found that i.p. benserazide alone can lead to pronounced increases in neostriatal dopamine and moderate increases of dihydroxyplenylacetic acid levels, whereas it did not affect homovanillic acid. Thus, not only the combination of L-DOPA (i.p. or intranasal) with the presumed peripheral L-DOPA decarboxylase inhibitor benserazide, but also each component alone can affect dopamine activity in the brain. Especially the findings with benserazide treatment might be of relevance for understanding the mechanisms of current L-DOPA therapy, since they indicate that part of the treatment's actions may possibly be determined by central dopaminergic effects of the accompanying amino acid decarboxylase inhibitor.

Extracellular adenosine levels in neostriatum and hippocampus during rest and activity periods of rats

Adenosine is an inhibitory modulator in the mammalian brain with a possible role in sleep regulation, which is mainly indicated by pharmacological studies showing that adenosine or its analogs can induce sedation and sleep, whereas adenosine antagonists, like caffeine and theophylline, are potent behavioral and neuronal stimulants. In contrast to these pharmacological findings, data on endogenous adenosine in relation to sleep and waking are sparse. Therefore, we have now used in vivo microdialysis to investigate the extracellular levels of adenosine in the neostriatum and hippocampus of freely moving rats. Adenosine was monitored over a time course of 24 h, during which the animals were exposed to a 12 h day/night rhythm with lights-off from 19.00 to 07.00. In this lights-off period, i.e. the rats' active period, the maximal levels of neostriatal and hippocampal extracellular adenosine were higher than during the lights-on period. In contrast to the neostriatum, extracellular levels of hippocampal adenosine tended to increase towards the end of the lights-off period, reaching its maximal level at 07.00, and decreasing again within the following hour. The changes of hippocampal adenosine levels were related to behavior, since significant increases in "sleep-like" behavior, as well as decreases in overall movements and consummatory behavior, were observed when adenosine levels had reached their maxima in the hippocampus; no such relationship was found with respect to the neostriatum. These results are in keeping with a role of endogenous adenosine in the regulation of sleep and wakefulness, and point to a specific role of adenosine in the hippocampus. They also raise the possibility that adenosine may be involved in different behavioral processes dependent on the area of the brain, as well as the type of adenosine receptor involved. Finally, given the known evidence for neuroprotective actions of adenosine, its accumulation in the hippocampus as a function of behavioral activity may serve to prevent or repair the neural degenerative consequences of such activity. It is proposed that adenosine's sleep-promoting effects result from its signalling to cease behavioral activity in order to prevent excessive activity-related changes, and thus allow other restorative sleep-related processes to take over.

The behavioral neurochemistry of motivation: methodological and conceptual issues in studies of the dynamic activity of nucleus accumbens dopamine

Considerable experimental and clinical evidence links forebrain dopamine (DA) systems to the performance of motor activities and to motivational processes. Much of the support for this conclusion was obtained from studies utilizing lesions or drugs to manipulate aspects of central dopaminergic function. Although such experiments yield important information concerning the behavioral consequences of interference with DA systems in brain, they do not demonstrate any relation between the dynamic activity of DA neurons and the level or type of motor function exhibited by the organism. This review discusses the emerging field of behavioral neurochemistry, and provides an overview of recent studies investigating the relation between nucleus accumbens DA release and behavior. Particular emphasis is placed upon current research involving microdialysis, voltammetry and electrophysiology. These different methods are viewed as complementary techniques for investigating the activity of DA systems in behaving animals. Evidence indicates that DA activity is most reliably activated by stimuli that trigger instrumental behavior and during the preparatory or instrumental phase of motivated behavior. The effects of consummatory reactions to positive reinforcers are somewhat equivocal; with food consumption, dialysis studies have yielded inconsistent results, while some voltammetric and electrophysiological studies have shown that DA activity in accumbens or ventral tegmental area actually decreases during consumption of food reinforcement. Moreover, the responsiveness of accumbens DA activity during behavioral stimulation is not unique to appetitive conditions, as several studies have shown that aversive or stressful conditions also stimulate accumbens DA release or metabolism. It is reasonable to suggest at this time that accumbens DA neurons are activated by a variety of different motivational conditions, but that the consequence of that activation is to modulate the behavioral reactivity of the organism. This type of function is seen as representing an area of overlap between motor and motivational processes.

Changes in extracellular levels of dopamine metabolites in somatosensory cortex after peripheral denervation

This study examined the effects of a nerve transection on monoamine release from primary somatosensory cortex. The technique of microdialysis was employed to sample extracellular levels of norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in the barrel field of freely moving rats following the surgical transection of the contralateral infraorbital nerve. Microdialysates obtained 3, 4, and 5 days after deafferentation were analyzed using high-performance liquid chromatography with electrochemical detection. We found a significant increase in the release of the dopamine metabolites, DOPAC and HVA from the deafferented cortex. Three days after deafferentation the release of DOPAC was three-fold higher in the deafferented than in the control animals, and remained about 100% higher in the next two days in this group of animals. The release of HVA showed a gradual increase following the deafferentation procedure, since a 92% larger value on day 3 increased to a 338% difference on day 5. On the other hand, the release rate of NE and the levels of the serotonin metabolite 5-HIAA were not significantly affected by the deafferentation procedure. These results are discussed in the context of the possible participation of dopamine in the reorganization of the deafferented somatosensory cortex.

Quantitative autoradiographic analysis of D1 and D2 dopamine receptors in rat brain in early and late pregnancy

This study examined the levels of D1 and D2 dopamine receptors in the rat brain during pregnancy, a physiologically unique and important naturally occurring state. We are particularly interested in changes in the dopamine receptor complement of the brain during pregnancy because these receptors might support some components of the immediate postpartum onset of normal maternal behavior. Quantitative in vitro receptor autoradiography was applied particularly focusing on brain areas that control maternal behavior. The D1 dopamine receptor selective antagonist -3H-SCH23390 and the D2 dopamine receptor selective antagonist [3H]spiperone were used as the ligands. We examined the levels of binding to D1 and D2 dopamine receptors in brains in females on day 2 (early pregnancy) and day 21 (late, but prepartum pregnancy) of pregnancy. In addition, brains from females on diestrus-1 and from males provided reference points to the existing literature. Late in pregnancy females had significantly 18-27% lower levels of binding to D1 dopamine receptors in the lateral striatum, the medial striatum, and the nucleus accumbens when compared to all other groups. Late in pregnancy, females had also significantly 11-25% lower levels of binding to D2 dopamine receptors in the lateral striatum, the anterior striatum, the nucleus accumbens and the olfactory tubercle compared to all other experimental groups. We examined all of the brain regions already established to be important for maternal behavior, and found that dopamine receptor binding changed across pregnancy only in one such region, the nucleus accumbens. Thus pregnancy, perhaps the hormones of pregnancy, reduces the levels of D1 and D2 dopamine receptors in the striatum, and the nucleus accumbens, but not in other brain regions.

Brain microdialysis and its application for the study of animal behaviour

Microdialysis is a sampling method that is used to determine the extracellular concentration of neurotransmitters in the brain. The method can be applied to conscious and unrestrained animals and is very suitable for the study of the chemistry of endogenous behaviour. This article reviews the contribution that microdialysis made to our understanding of the chemistry of behaviour. Methodological and practical considerations such as the implantation time and the use of guide cannulas are reviewed. The question whether neurotransmitters and related metabolites in dialysates reflect true synaptic release is critically discussed. There is much evidence that dopamine, noradrenaline, acetylcholine and serotonin in dialysates are related to neurotransmission, but there is serious doubt whether this is the case with amino acid transmitters such as GABA, glutamate and aspartate. Until now far over 100 papers appeared that used microdialysis in behavioural studies. Behavioural activation, the sleep-awake cycle and diurnal rhythms were subject of several of these studies. Various workers have described neurochemical changes in the brain that are related to feeding. Other studies were concerned with sexual behaviour and the sexual cycle in females. Parturition, maternal behaviour and offspring recognition have been studied in a series of microdialysis studies carried out in sheep. An overview is given of the microdialysis studies that were carried out to understand the biochemistry of stress. In this respect dopamine and noradrenaline have received much attention. A great number of microdialysis studies dealt with the role of dopamine in self-stimulation, reward and aversive emotions. It is concluded that microdialysis is at presently the most versatile and practical method to study the chemistry of behaviour and it is to be expected that it will soon be a routine methodology in behavioural research. Finally, perspectives and possible future developments of the methods are discussed.

Relationship between dopamine release in nucleus accumbens and place preference induced by substance P injected into the nucleus basalis magnocellularis region

The activity of the neurotransmitter dopamine in the nucleus accumbens is considered to be an important element in the central processing of reinforcement. Unilateral administration of the neurokinin substance P into the area of the nucleus basalis magnocellularis of rats was found to be reinforcing, as assessed by the conditioned place preference paradigm. Simultaneous in vivo microdialysis showed that administration of substance P into the area of the nucleus basalis magnocellularis could increase extracellular concentrations of dopamine in the contralateral nucleus accumbens. Only those animals in which the administration of substance P induced this increase in dopamine levels acquired place preference. Furthermore, the changes in extracellular dopamine levels after substance P administration had a bimodal time course with an acute increase (to about 160% of baseline) during the first hour after injection, with a low (to 120-130%) and enduring increase occurring thereafter. Interestingly, during this second increase there were indications for positive correlations with the degree of place preference induced by substance P. Further positive correlations with place preference were found in the levels of the serotonergic metabolite 5-hydroxyindoleacetic acid. In contrast to dopamine, these were observed ipsi- and contralateral to the side of substance P administration. By combining the methods of in vivo microdialysis and conditioned place preference it was shown that the reinforcing effect induced by unilateral substance P injection in the nucleus basalis magnocellularis is related to dopaminergic (and possibly serotonergic) mechanisms in the nucleus accumbens.

The role of neuropeptides in learning: focus on the neurokinin substance P

The neurokinin substance P (SP) can have neurotrophic as well as memory-promoting effects. The study of its mechanisms may provide new insights into processes underlying learning and neurodegenerative disorders. Our work shows that SP, when applied peripherally (i.p.), promotes memory and is reinforcing at the same dose of 37 nmol/kg. Most important, however, is the finding that these effects seemed to be encoded by different SP-sequences, since the N-terminal SP1-7 (185 nmol/kg) enhanced memory, whereas C-terminal hepta- and hexapeptide sequences of SP proved to be reinforcing in a dose equimolar to SP. These differential behavioral effects were paralleled by selective and site-specific changes in dopamine (DA) activity, as both SP and its C-, but not N-terminus, increased extracellular DA in the nucleus accumbens (NAc), but not in the neostriatum. The neurochemical changes lasted at least 2 h after injection. Direct application of SP (0.74 pmol) into the region of the nucleus basalis magnocellularis (NBM) was also memory-promoting and reinforcing, and again, these effects were differentially produced by the N-terminus and C-terminus, supporting the proposed structure-activity relationship for SP's effects on memory and reinforcement. In addition, it was found that a single injection of SP into the NBM led to an increase of extracellular DA in the contralateral NAc. This effect of SP was observed only in those animals where SP was reinforcing, providing evidence for a lateralized relationship between reinforcement induced by injection of SP into the NBM and DA activity in the NAc. Furthermore, the outcome of a series of experiments suggests, that SP may not only be considered to have memory-promoting effects in normal animals, but can also improve functional recovery after unilateral 6-OHDA lesion of the substantia nigra and after lesions of the hippocampus, and can counteract age-related performance deficits.

Role of the nucleus accumbens and the striatum in the production of turning behaviour in intact rats

Recent knowledge of the mechanisms underlying turning or circling behaviour in intact rats is reviewed. Most interest has been directed towards the striatum because of the classical hypothesis that turning behaviour results from lateral differences in the activity of the bilateral nigrostriatal pathway. However, the assumption that asymmetrical activation of the striatum is a necessary condition for dopamine-dependent turning behaviour has been questioned by several studies showing that unilateral injection of amphetamine or dopamine receptor agonists into the nucleus accumbens, a target of the mesolimbic dopaminergic system, also produces reliable circling away from the side of injection. Apart from discussing differences in stepping patterns of turning and discussing the role of the dopamine D1/D2 receptor interaction, the present survey focuses attention upon the two-component hypothesis, especially in relation to our recent studies in which activities of dopamine D1 and D2 receptors in the striatum and the nucleus accumbens have been manipulated separately in intact rats. It is hypothesized that turning behaviour is produced by asymmetry within nucleus accumbens circuits which involve neuronal connections from the nucleus accumbens to the A9 cell area, which in turn projects to the ventrolateral striatum that determines the direction of turning.

Behavioral and neurochemical asymmetries following unilateral trephination of the rat skull: is this control operation always appropriate?

The present results are from rats that were intended as sham-operated controls in a study of unilateral lesion of the cortical barrel fields. These animals received a trephine hole through the skull, centered over the barrel fields of one hemisphere. Unexpectedly, they showed time-dependent behavioral and neurochemical asymmetries: 1 + 4 days after unilateral skull trephination they scanned an open field mainly with the contralateral vibrissae. Thereafter (days 7 + 14), scanning recovered to symmetry; however, an ipsilateral asymmetry was induced now by challenge with the dopamine receptor agonist apomorphine. At the same time period after skull trephination, an asymmetry of thigmotactic swimming had developed, with more thigmotactic swimming ipsilateral to the side of skull trephination. Neurochemically, there were indications for changes in neostriatal dopamine metabolism because the tissue levels of dopamine and dihydroxyphenylacetic acid were lower on the ipsilateral side in animals killed 6-16 days after trephination. The time courses of behavioral and neurochemical asymmetries after unilateral skull trephination paralleled those seen following unilateral barrel cortex lesion or unilateral removal of the corresponding contralateral vibrissae; however, without exception, the asymmetries after trephination were in the opposite direction than after cortex lesion or vibrissae removal. The possible mechanisms by which skull trephination might have affected behavior and neurochemistry are discussed, especially with respect to the vibrissae-barrel cortex system and the basal ganglia. Because trephination of the skull is routinely employed, both as a control procedure and for CNS manipulation, these results may have important implications for the design of future experiments.

Unilateral stimulation or removal of rat vibrissae: analysis of nerve growth factor and tyrosine hydroxylase mRNA in the brain

Previous work has shown that unilateral manipulation of vibrissae in the rat can lead to behavioral asymmetries and to neuronal changes in the basal ganglia: in brief, vibrissae stimulation led to increases in neostriatal dopamine release, whereas unilateral removal of vibrissae led to asymmetries in striatal afferents and to bilateral changes in mesencephalic dopamine mechanisms which were related to the occurrence of behavioral asymmetries and the later recovery therefrom. In the present study, the analysis of neuronal mechanisms possibly affected by vibrissae manipulation was extended to the nerve growth factor and the expression of tyrosine hydroxylase mRNA. Unilateral stimulation or removal of the vibrissae did not lead to significant changes in tissue levels of nerve growth factor in the neostriatum, parietal cortex (including the barrel cortex) or the hippocampus. In contrast, tyrosine hydroxylase mRNA in the substantia nigra and ventral tegmental area was affected by vibrissae removal but not by stimulation, as a bilateral increase in labeling was observed on the level of individual neurons. This effect was only observed in animals tested 4 h after vibrissae removal but not after 10 days. The results are discussed with respect to the interaction of vibrissae function with the basal ganglia, the neurotransmitter dopamine and mechanism of functional recovery.

Stress-induced dopamine release in the neostriatum: evaluation of the role of action potentials in nigrostriatal dopamine neurons or local initiation by endogenous excitatory amino acids

It has been hypothesized that excitatory amino acids can initiate dopamine release in neostriatum. We examined whether the increase in extracellular dopamine in neostriatum produced by acute stress reflects presynaptic initiation of dopamine release by endogenous excitatory amino acids. Thirty minutes of intermittent tail-shock stress significantly elevated extracellular concentrations of dopamine, glutamate, aspartate, and gamma-aminobutyric acid in neostriatum of freely moving rats as measured with in vivo microdialysis. Local infusion of the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovalerate or the non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione via the dialysis probe did not attenuate the stress-induced increase in extracellular dopamine. In fact, the increase was prolonged in rats treated with specific excitatory amino acid receptor antagonists. Infusion of tetrodotoxin into medial forebrain bundle increased extracellular glutamate and aspartate in neostriatum yet reduced basal dopamine in extracellular fluid to below the limit of detection of the assay and eliminated the stress-induced increase in extracellular dopamine. These findings fail to support the hypothesis that the stress-induced increase in extracellular dopamine in neostriatum is initiated locally by excitatory amino acids. Rather, the effects of stress on extracellular dopamine seem to be determined by impulse propagation in dopamine neurons.

Interaction with pups enhances dopamine release in the ventral striatum of maternal rats: a microdialysis study

A growing body of evidence suggests that an interference with dopamine (DA) transmission disrupts maternal behavior in the rat. The present brain microdialysis study was therefore conducted to investigate whether infants can modulate ventral striatal DA release in mother rats. There was a significant rise in the extracellular concentrations DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in the ventral striatum when mothers were reunited with their litters following separation overnight. Nursing was the predominant behavior during this phase of the experiment. More active behaviors were elicited by soiling pups with flowerpot earth, and this was accompanied by further increases in DA, DOPAC, HVA, and 5-HIAA. It is suggested that pup-induced stimulation of ventral striatal DA release facilitates parental responses such as pup retrieval.

Sequence-specific effects of neurokinin substance P on memory, reinforcement, and brain dopamine activity

There is ample evidence that the neurokinin substance P (SP) can have neurotrophic as well as memory-promoting effects. This paper outlines a recent series of experiments dealing with the effects of SP and its N- and C-terminal fragments on memory, reinforcement, and brain monoamine metabolism. It was shown that SP, when applied peripherally (IP), promotes memory (inhibitory avoidance learning) and is reinforcing (place preference task) at the same dose of 37 nmol/kg. Most important, however, is the finding that these effects seemed to be encoded by different SP sequences, since the N-terminal SP1-7 (185 nmol/kg) enhanced memory, whereas C-terminal hepta- and hexapeptide sequences of SP proved to be reinforcing in a dose equimolar to SP. These differential behavioral effects were paralleled by selective and site-specific changes in dopamine (DA) activity, as both SP and its C-, but not N-terminus, increased extracellular DA in the nucleus accumbens (NAc), but not in the neostriatum. The neurochemical changes lasted at least 2 h after injection. These results show that the reinforcing action of peripheral administered SP may be mediated by its C-terminal sequence, and that this effect could be related to DA activity in the NAc. Direct application of SP (0.74 pmol) into the region of the nucleus basalis magnocellularis (NBM) was also memory-promoting and reinforcing, and again, these effects were differentially produced by the N-terminus and C-terminus, supporting the proposed structure-activity relationship for SP's effects on memory and reinfrocement. These results may provide a hypothetical link between the memory-modulating and reinforcing effects of SP and the impairment in associative functioning accompanying certain neurodegenerative processes.

Peripherally administered substance P affects extracellular dopamine concentrations in the neostriatum but not in the nucleus accumbens under anesthesia

The in situ microdialysis technique was used in urethane-anesthetized rats to monitor changes in the extracellular concentrations of dopamine and its metabolites in neostriatum and nucleus accumbens after the peripheral administration of substance P (50 or 250 micrograms/kg, IP). Four to five hours after urethane anesthesia a decrease of extracellular dopamine and its metabolites was observed which continued in the nucleus accumbens in the following 3 h. The administration of substance P induced a decrease in extracellular concentration of dopamine in neostriatum. This neurochemical change after substance P was not accompanied by parallel alterations in extracellular concentrations of dopamine metabolites. No effects of substance P were observed on dopamine or its metabolites in nucleus accumbens. These data are discussed in relation with the contrasting effects of substance P on awake rats and the possible changes in striatal dopamine activity induced by anesthetics.

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.

The C-terminal fragment of substance P enhances dopamine release in nucleus accumbens but not in neostriatum in freely moving rats

The in vivo microdialysis technique was used to study the effects of carboxyl or amino terminal sequences of substance P on the extracellular concentrations of dopamine, its metabolites dihydroxyphenylacetic acid and homovanillic acid, as well as on 5-hydroxyindoleacetic acid, in neostriatum and nucleus accumbens of freely moving rats. The i.p. administration of 37 nmol/kg of the substance P C-terminal heptapeptide analog [pGlu5, MePhe8, Sar9]SP5-11 (DiMe-C7) caused an increase in extracellular dopamine concentrations in nucleus accumbens but not in neostriatum. The administration of the equimolar dose of the heptapeptide N-terminal fragment substance P 1-7 (SP1-7) did not have an effect in either structure. No changes were observed in the extracellular concentrations of the metabolites after the administration of either substance. These results are discussed with respect to the reinforcing effects of substance P and its C-terminal sequence, which may be mediated via dopamine release in the nucleus accumbens.

Effects of substance P on extracellular dopamine in neostriatum and nucleus accumbens

Microdialysis was used to monitor changes in dopamine release in the neostriatum and nucleus accumbens after peripheral administration of substance P in freely moving rats. Substance P in a dose of 50 micrograms/kg produced a steady moderate increase in dopamine levels in the neostriatum, which persisted for at least 5 h. In contrast, a dose of 250 micrograms/kg caused an acute increase in dopamine levels in the nucleus accumbens, which lasted about 2 h. These data suggest that the peripheral administration of substance P can influence dopamine release in mesolimbic and mesostriatal terminals.

Behavioral concomitants of regional changes in the brain's biogenic amines after apomorphine and amphetamine

Behavioral and neurochemical changes were analyzed in rats after systemical injections of the dopamine receptor agonist apomorphine (0.5 mg/kg) or the indirect agonist amphetamine (1.0 mg/kg). As expected, amphetamine led to an increase in locomotion, whereas apomorphine resulted in decreases in locomotion, rearings, and grooming. The analysis of biogenic amines in tissue samples showed that amphetamine decreased 3,4-dihydroxy-phenylacetic acid (DOPAC) levels and DOPAC/dopamine ratios in the neostriatum, and resulted in a lower 5-hydroxyindole-3-acetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) ratio in the ventral mesencephalon. Apomorphine decreased the dopamine metabolites [DOPAC, homovanillic acid (HVA), 3-methoxy-tyramine (3-MT)] and their respective metabolite/transmitter ratios and increased dopamine levels in the neostriatum. Similar decreases in dopamine metabolites or their ratios were found in the ventral mesencephalon, septum, and frontoparietal cortex but not the thalamus. In addition to its effects on dopamine, apomorphine decreased norepinephrine in the ventral neostriatum and 5-HT and 5-HIAA in the cortex. Correlations between behavioral activity and neurochemical metabolism (using the metabolite-transmitter ratios for the latter) revealed relationships between locomotion and serotonergic activity in the thalamus of animals treated with amphetamine. Evidence for a relationship between locomotion or rearings and dopaminergic activity was found in all six brain areas analyzed. Here, the pattern of correlation was dependent on the kind of treatment and the behavioral and neurochemical measures. These results support earlier findings on the neurochemical effects of apomorphine and amphetamine in the neostriatum and ventral mesencephalon, and add new evidence for an action on the septal area, thalamus, and frontoparietal cortex.

Control of turning behavior under apomorphine by sensory input from the face

It has been shown that peripheral manipulation of sensory input by removal of vibrissae on one side of the rat's face induces turning behavior which is directed towards the contralateral vibrissae-intact side, under the influence of the dopamine receptor agonist apomorphine. In the present experiment, we examined whether rats under apomorphine turn towards the side with more sensory input, or simply away from the manipulated side. Thus, an experimental manipulation was designed to increase sensory input. Sensory stimulation was applied by attaching a clip into the fur on one side of the face. Rats injected with apomorphine in doses of 0.5-5.0 mg/kg (but not with 0.05 mg/kg or vehicle) exhibited turning behavior towards the side of the clip. This sensory stimulation was also found to influence spontaneous behavioral asymmetries. These results show that an imbalance in sensory input is sufficient to produce turning under apomorphine.