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

Repetitive transcranial magnetic stimulation transiently reduces punding in Parkinson's disease: a preliminary study

Amongst the impulse-control disorders (ICDs) associated with dopamine-replacement therapy in patients with Parkinson's disease (PD) is a repetitive, complex, stereotyped behaviour called punding. Disruption of the reciprocal loops between the striatum and structures in the prefrontal cortex (PFC) following dopamine depletion may predispose patients with PD to these behavioural disorders. The purpose of the present study was to assess the effects of repetitive transcranial magnetic stimulation (rTMS) over the dorsolateral PFC (DLPFC) on punding in PD. We used low-frequency (LF) rTMS in four PD patients presenting with punding. Punding was transiently reversed by LF-rTMS over the DLPFC without enhancing motor impairment. The effect was more sustained after right DLPFC rTMS. Therefore, LF-rTMS produced a transient beneficial effect in PD patients with punding, similar to that reported in PD patients with levodopa-induced dyskinesias. rTMS might have therapeutic potential for the treatment of punding and perhaps other ICDs in PD.

Insights into pathophysiology of punding reveal possible treatment strategies

Punding is a stereotyped behavior characterized by an intense fascination with a complex, excessive, nongoal oriented, repetitive activity. Men tend to repetitively tinker with technical equipment such as radio sets, clocks, watches and car engines, the parts of which may be analyzed, arranged, sorted and cataloged but rarely put back together. Women, in contrast, incessantly sort through their handbags, tidy continuously, brush their hair or polish their nails. Punders are normally aware of the inapposite and obtuse nature of the behavior; however, despite the consequent self-injury, they do not stop such behavior. The most common causes of punding are dopaminergic replacement therapy in patients affected by Parkinson's disease (PD) and cocaine and amphetamine use in addicts. The vast majority of information about punding comes from PD cases. A critical review of these cases shows that almost all afflicted patients (90%) were on treatment with drugs acting mainly on dopamine receptors D1 and D2, whereas only three cases were reported in association with selective D2 and D3 agonists. Epidemiological considerations and available data from animal models suggest that punding, drug-induced stereotypies, addiction and dyskinesias all share a common pathophysiological process. Punding may be related to plastic changes in the ventral and dorsal striatal structures, including the nucleus accumbens, and linked to psychomotor stimulation and reward mechanisms. Possible management guidelines are proposed.

Human methamphetamine pharmacokinetics simulated in the rat: behavioral and neurochemical effects of a 72-h binge

Bingeing is one pattern of high-dose methamphetamine (METH) abuse, which involves continuous drug taking over several days and can result in psychotic behaviors for which the brain pathology remains poorly defined. A corresponding animal model of this type of METH exposure may provide novel insights into the neurochemical and behavioral sequelae associated with this condition. Accordingly, to simulate the pharmacokinetic profile of a human METH binge exposure in rats, we used a computer-controlled, intravenous METH procedure (dynamic infusion, DI) to overcome species differences in METH pharmacokinetics and to replicate the human 12-h plasma METH half-life. Animals were treated over 13 weeks with escalating METH doses, using DI, and then exposed to a binge in which drug was administered every 3 h for 72 h. Throughout the binge, behavioral effects included unabated intense oral stereotypies in the absence of locomotion and in the absence of sleep. Decrements in regional brain dopamine, norepinephrine, and serotonin levels, measured at 1 and 10 h after the last injection of the binge, had, with the exception of caudate-putamen dopamine and frontal cortex serotonin, recovered by 48 h. At 10 h after the last injection of the binge, [(3)H]ligand binding to dopamine and vesicular monoamine transporters in caudate-putamen were reduced by 35 and 13%, respectively. In a separate METH binge-treated cohort, post-binge behavioral alterations were apparent in an attenuated locomotor response to a METH challenge infusion at 24 h after the last injection of the binge. Collectively, the changes we characterized during and after a METH binge suggest that for human beings under similar exposure conditions, multiple time-dependent neurochemical deficits contribute to their behavioral profiles.

Psychostimulant treatment for ADHD is modulated by prefrontal cortex manipulation

The psychostimulant amphetamine (Amph) is widely used treatments for attention-deficit hyperactivity disorder (ADHD). Chronic intermittent exposure to psychostimulants induces behavioral sensitization. The objective of this study was to investigate the role of prefrontal cortex (PFC) in the acute and chronic effect of Amph using the open-field assay. Male Sprague-Dawley rats were assigned randomly to three groups, (1) an intact control group (2) a PFC sham-operated group, and (3) a PFC lesion group. All the three groups showed increases in locomotor activity after acute amphetamine injection (P<0.05), and activity levels were especially augmented in PFC lesion group. Following chronic amphetamine, the control group and sham-operated group exhibited behavioral sensitization (P<0.05). However, the PFC lesion group failed to exhibit behavioral sensitization and the pattern of locomotion was altered, which indicated that the nature of behavioral sensitization was changed. The results suggest that PFC lesion enhance the acute effects of amphetamine on locomotor activity and is required for development of behavior sensitization.

Neurotoxic lesions of the caudate-putamen on a reaching for food task in the rat: acute sensorimotor neglect and chronic qualitative motor impairment follow lateral lesions and improved success follows medial lesions

Reaching for food, or skilled reaching, is used as a test of basal ganglia function in preclinical studies as well as studies of human neurological conditions. Although changes in the end-point measure of success document the effects of neurotoxic cellular damage to the caudate-putamen and its treatment in rodents, there has been no examination of the cause of change in success after neurotoxic lesions of the striatum. This objective was addressed in the present study, in which rats trained to reach for single food pellets with one forelimb, received contralateral quinolinic acid or ibotenic acid lesions of the medial and lateral caudate-putamen. Over 21 postsurgical days, reaching performance was scored for success and qualitative changes in movement elements were examined using frame-by-frame video analysis. In the acute postoperative period, extending over 3 to 4 days, the rats with lateral lesions transported their forelimb and grasped the food, but then ignored the food and did not withdraw their limb to their mouth. After recovery of the withdrawal movement, the rats displayed chronic qualitative impairments in the rotatory movements of aiming, pronating, and supinating the forepaw. Medial quinolinic lesions improved success relative to control rats and did not change qualitative aspects of limb movement. The acute dissociation between transport and withdrawal, the chronic qualitative changes in movement elements, and the differential effect of medial and lateral injury on success, support a complex contribution of the caudate-putamen to skilled reaching that includes sensorimotor neglect, and quantitative and qualitative motoric changes.

Isolation rearing or methamphetamine traumatisation induce a "dysconnection" of prefrontal efferents in gerbils: implications for schizophrenia

A miswiring of prefrontal efferents is generally discussed by the name of "dysconnection" as the anatomical substrate of schizophrenia. Since direct histological confirmation of this hypothesis can hardly be obtained in humans, we used an animal model of schizophrenia to trace prefrontal efferents to distal cortical fields. Mongolian gerbils were intoxicated with a single high dose of methamphetamine on postnatal day 14 and reared in isolation after weaning (day 30). Controls received a saline injection and/or were reared under enriched conditions. Upon reaching adulthood (day 90), biocytin was injected into the medial prefrontal cortex into either deep or superficial laminae. The density of passing fibres and terminal fields in the frontal, parietal and insular cortices was assessed by digital image analysis. Isolation rearing or methamphetamine treatment alone reduced the projections from lamina V/VI to the frontal and from lamina III to the insular cortex, and from both laminae to the parietal cortex. In contrast, isolation rearing of methamphetamine-intoxicated gerbils significantly increased the projections from the deep laminae to the frontal and parietal cortices, compared to isolation-reared controls, with no difference in the efferents from superficial laminae. These results are the first to demonstrate a miswiring of prefrontal efferents in response to adverse systemic influences. They might give a hint at the anatomical basis of "dysconnection" in schizophrenia.

Punding in Parkinson's disease: its relation to the dopamine dysregulation syndrome

Punding is a term that was coined originally to describe complex prolonged, purposeless, and stereotyped behaviour in chronic amphetamine users. A structured interview of 50 patients with higher dopamine replacement therapy requirements (>800 levodopa equivalent units/day) from 123 unselected patients with Parkinson's disease (PD) from a PD clinic identified 17 (14%) patients with punding. Punding was acknowledged as disruptive and unproductive by the patients themselves, but forcible attempts by family to interrupt the behaviour led to irritability and dysphoria. Punding was associated with very high doses of dopamine replacement therapy often related to a pattern of chronic inappropriate overuse of dopaminergic medication. We believe that this is an underreported, socially disabling phenomenon that is commonly associated with the syndrome of dopamine dysregulation and is phenomenologically distinct from both obsessive-compulsive disorder and mania.

In vivo evidence that genetic background controls impulse-dependent dopamine release induced by amphetamine in the nucleus accumbens

Amphetamine is known to increase dopamine (DA) release by acting directly on dopamine transporters (DAT), primarily through a mechanism that is independent of impulse flow. We present evidence to show that impulse-dependent increase in DA outflow in the nucleus accumbens (NAc) is produced by amphetamine depending on genetic background. Systemic amphetamine produced higher accumbal DA release in the widely exploited C57BL/6J background than in the DBA/2J. By contrast, intra-accumbens perfusion using increasing doses of amphetamine dramatically increased DA outflow in the DBA/2J background, whereas very low DA outflow was evident in C57BL/6J mice. The fast sodium channel blocker tetrodotoxin infused through the microdialysis probe abolished accumbal DA release induced by systemic amphetamine only in the C57BL/6J background. Finally, medial prefrontal excitotoxic lesion abolished amphetamine-induced mesoaccumbens DA release in C57BL/6J mice, without significantly affecting it in the DBA/2J background. These results represent the first functional evidence in an in vivo study that amphetamine can increase DA release in the NAc mainly through an impulse-dependent mechanism regulated by prefronto-cortical glutamatergic transmission. Moreover, they point to a genetic control of impulse-dependent DA release in the accumbens, providing an exploitable tool to investigate aetiological factors involved in psychopathology and drug addiction.

Compulsive use of dopamine replacement therapy in Parkinson's disease: reward systems gone awry?

Dopamine replacement therapy (DRT) is the most effective treatment for Parkinson's disease (PD); it provides substantial benefit for most patients, extends independence, and increases survival. A few patients with PD, however, take increasing quantities of medication far beyond those required to treat their motor disabilities. These patients demand rapid drug escalation and continue to request more DRT despite the emergence of increasingly severe drug-induced motor complications and harmful behavioural consequences. In this article we detail the features of compulsive DRT-seeking and intake in PD, in relation to theories of compulsive drug use.

A role for presynaptic mechanisms in the actions of nomifensine and haloperidol

Psychomotor stimulants and neuroleptics exert multiple effects on dopaminergic signaling and produce the dopamine (DA)-related behaviors of motor activation and catalepsy, respectively. However, a clear relationship between dopaminergic activity and behavior has been very difficult to demonstrate in the awake animal, thus challenging existing notions about the mechanism of these drugs. The present study examined whether the drug-induced behaviors are linked to a presynaptic site of action, the DA transporter (DAT) for psychomotor stimulants and the DA autoreceptor for neuroleptics. Doses of nomifensine (7 mg/kg i.p.), a DA uptake inhibitor, and haloperidol (0.5 mg/kg i.p.), a dopaminergic antagonist, were selected to examine characteristic behavioral patterns for each drug: stimulant-induced motor activation in the case of nomifensine and neuroleptic-induced catalepsy in the case of haloperidol. Presynaptic mechanisms were quantified in situ from extracellular DA dynamics evoked by electrical stimulation and recorded by voltammetry in the freely moving animal. In the first experiment, the maximal concentration of electrically evoked DA ([DA](max)) measured in the caudate-putamen was found to reflect the local, instantaneous change in presynaptic DAT or DA autoreceptor activity according to the ascribed action of the drug injected. A positive temporal association was found between [DA](max) and motor activation following nomifensine (r=0.99) and a negative correlation was found between [DA](max) and catalepsy following haloperidol (r=-0.96) in the second experiment. Taken together, the results suggest that a dopaminergic presynaptic site is a target of systemically applied psychomotor stimulants and regulates the postsynaptic action of neuroleptics during behavior. This finding was made possible by a voltammetric microprobe with millisecond temporal resolution and its use in the awake animal to assess release and uptake, two key mechanisms of dopaminergic neurotransmission. Moreover, the results indicate that presynaptic mechanisms may play a more important role in DA-behavior relationships than is currently thought.

Amphetamine sensitization of hallucinatory-like behaviors is dependent on prefrontal cortex in nonhuman primates

BACKGROUND

Repeated amphetamine (AMPH) exposure in nonhuman primates produces a chronic state of monoamine dysregulation and long-lasting changes in behaviors elicited by acute AMPH (including tracking, grasping "at thin air," manipulating nonapparent stimuli, and hypervigilance) in a manner that bears a marked resemblance to symptoms of both amphetamine psychosis and paranoid schizophrenia. These abnormal responses have historically been referred to as psychotomimetic or hallucinatory-like. In contrast to negative symptoms and cognitive deficits, the positive symptoms of schizophrenia including hallucinations have not traditionally been linked to prefrontal dysfunction.

METHODS

The dorsomedial (9/8B), dorsolateral (46/8A), and inferior (45/12) sectors of prefrontal cortex were lesioned, singly or in combination. Lesioned and nonlesioned control monkeys were sensitized over a 6-week period using an intermittent schedule of escalating low doses of AMPH. Behavioral responses to acute AMPH after chronic exposure were compared with preexposure responses.

RESULTS

Bilateral lesions of prefrontal cortex performed before subchronic AMPH suppressed the sensitization of hallucinatory-like behaviors but markedly enhanced locomotor sensitization compared with control animals.

CONCLUSION

These findings indicate that the primate prefrontal cortex may be a substrate for the development of the full complement of behaviors elicited by AMPH sensitization, including hallucinatory-like behaviors.

Norepinephrine in the prefrontal cortex is critical for amphetamine-induced reward and mesoaccumbens dopamine release

Increasing evidence points to a major involvement of cortical areas in addictive mechanisms. Noradrenergic transmission in the medial prefrontal cortex (mpFC) has been shown to affect the motor effects of amphetamine, although there is no evidence of its involvement in the rewarding effects of this psychostimulant. The present experiments were aimed at investigating the possibility of a selective involvement of prefrontal cortical norepinephrine (NE) in the rewarding-reinforcing effects of amphetamine. To do so, we evaluated the effects of mpFC NE selective depletion in mice of C57BL/6J inbred strain, a background commonly used in molecular approaches that is known to be highly susceptible to the rewarding effects of the psychostimulant. In a first set of experiments, we demonstrated the absence of amphetamine-induced conditioned place preference in mice bearing prefrontal NE depletion. In a second series of experiments, we demonstrated that the same lesion dramatically reduced amphetamine-induced mesoaccumbens dopamine release as measured by intracerebral microdialysis. These results indicate that noradrenergic prefrontal transmission, by allowing increased dopamine release in the nucleus accumbens induced by amphetamine, is a critical factor for the rewarding-reinforcing effects of this drug.

Sulpiride alleviates the attentional impairments of rats with medial prefrontal cortex lesions

Recent studies have shown that medial prefrontal cortex (mPFC) lesions impair performance on a number of rodent tests of attention. Although this evidence clearly suggests a role for the rat mPFC in attentional functions, it is unclear whether subcortical changes associated with mPFC lesions might also be relevant to the neuropsychological deficits observed. Given the ample evidence suggesting increased dopaminergic mechanisms in the basal ganglia following mPFC lesions, we investigated the effects of dopamine receptor agonists and antagonists on the attentional deficits associated with mPFC lesions. Rats trained on a five-choice reaction time task received either complete mPFC lesions or lesions restricted to its ventral subregions, the prelimbic and infralimbic cortices (PRL-IL). Compared with sham-operated rats, animals in both the lesioned groups were impaired at responding correctly to the visual targets, although this deficit was more marked in mPFC-lesioned rats. In addition, both lesions were associated with increased perseverative responding. The accuracy deficits of rats with mPFC lesions were alleviated by systemic administration of the dopamine D2 receptor antagonist sulpiride. In contrast, rats with PRL-IL damage were not affected and control rats were impaired by sulpiride. Administration of either the dopamine D1 receptor antagonist SCH 23390 or of pre-synaptic doses of apomorphine had similar, albeit non-significant effects. Higher doses of any of these drugs non-specifically impaired performance. These results extend previous findings of attentional impairments in rats with mPFC lesions and are compatible with recent hypotheses concerning the role of dopaminergic dysregulation in the pathogenesis of schizophrenia.

Brain microdialysis in exercise research

During the last 5 to 10 years, the microdialysis technique has been used to explore neurotransmitter release during exercise. Microdialysis can collect virtually any substance from the brains of freely moving animals with a limited amount of tissue trauma. It allows the measurement of local neurotransmitter release in combination with ongoing behavioural changes such as exercise. Several groups examined the effect of treadmill running on extracellular neurotransmitter levels. Microdialysis probes were implanted in different brain areas to monitor diverse aspects of locomotion (striatum, hippocampus, nucleus accumbens, frontal cortex, spinal cord), food reward (hypothalamus, hippocampus, cerebral cortex), thermoregulation (hypothalamus). Some studies combined microdialysis with running on a treadmill to evaluate motor deficit and improvement following dopaminergic grafts in 6-hydroxydopamine lesioned rats, or combined proton nuclear magnetic resonance spectroscopy and cortical microdialysis to observe intra- plus extracellular brain glucose variations. This method allows us to understand neurotransmitter systems underlying normal physiological function and behaviour. Because of the growing interest in exercise and brain functioning, it should be possible to investigate increasingly subtle behavioural and physiological changes within the central nervous system. There is now compelling evidence that regular physical activity is associated with significant physiological, psychological and social benefits in the general population. In contrast with our knowledge about the peripheral adaptations to exercise, studies relating exercise to brain neurotransmitter levels are scarce. It is of interest to examine the effect of short and long term exercise on neurotransmitter release, since movement initiation and control of locomotion have been shown to be related to striatal neurotransmitter function, and one of the possible therapeutic modalities in movement, and mental disorders is exercise therapy. Until very recently most experimental studies on brain chemistry were conducted with postmortem tissue. However, in part because of shortcomings with postmortem methods, and in part because of the desire to be able to directly relate neurochemistry to behaviour, there has been considerable interest in the development of 'in vivo' neurochemical methods. Because total tissue levels may easily mask small but important neurochemical changes related to activity, it is important to sample directly in the extracellular compartment of nervous tissue in living animals. Since the chemical interplay between cells occurs in the extracellular fluid, there was a need to access this compartment in the intact brain of living and freely moving animals. Estimation of the transmitter content in this compartment is believed to be directly related to the concentration at the site where these compounds are functionally released: in the synaptic cleft. As measurements in the synapse are not yet possible, in vivo measurements in the extracellular fluid appear to provide the most directly relevant information currently available. This article provides an overview of the in vivo microdialysis technique as a method for measuring in the extracellular space, and its application in exercise science. Although this technique has been used in different tissues such as brain, adipose tissue, spinal cord and muscle, in animals as well as humans, we will focus on the use of this in vivo method in brain tissue. Recently two excellent reviews on the application of microdialysis in human experiments especially in subcutaneous tissue have been published, and we refer the interested reader to these articles.

The effects of dopamine D(1) receptor blockade in the prelimbic-infralimbic areas on behavioral flexibility

This study examined the effects of a dopamine D(1) antagonist, SCH23390, infused into the prelimbic-infralimbic areas on the acquisition of a response and visual-cue discrimination task, as well as a shift from a response to a visual-cue discrimination and vice versa. Each test was carried out in a cross-maze. The response discrimination required learning to always turn in the same direction (right or left) for a cereal reinforcement. The visual-cue discrimination required learning to always enter the arm with the visual cue. In experiment 1, rats were tested on the response discrimination task, followed by the visual-cue discrimination task. In experiment 2, the testing order was reversed. Bilateral infusions of SCH23390 (0.1 or 1 microg/0.5 microL) into the prelimbic-infralimbic areas did not impair acquisition of the response or visual-cue discrimination tasks. SCH23390 injections at 1 microg, but not 0.1 microg impaired performance when shifting from a response to a visual-cue discrimination, and vice versa. Analysis of the errors revealed that the deficit was due to perseveration of the previously learned strategy. These results suggest that activation of dopamine D(1) receptors in the prelimbic-infralimbic areas may be critical for the suppression of a previously relevant strategy and/or generating new strategies.

Medial prefrontal transection enhances social interaction. I: behavioral studies

Behavioral effects of a medial prefrontal cortex (MPFC) transection were assessed in animal tests of anxiety. Social investigation and plus-maze open arm exploration increased in MPFC damaged animals relative to sham ones. MPFC lesions prevented D-amphetamine (2 mg/kg, i.p.) induced social investigation decrease and exaggerated general locomotion increase. Diazepam (1 mg/kg, i.p.) and MPFC synergistically increased open arm exploration on a second (repeated) plus-maze trial. These results suggest that the MPFC would be implicated in a generalized mechanism of warning enabling emission of appropriate responses to anxiogenic stimuli. Although, this lesion did not modify motor activity itself, the pattern of the motor activation induced by amphetamine was altered. The role of the MPFC areas in the behavioral response associated with fear is discussed.

Is there an optimal age for recovery from motor cortex lesions? I. Behavioral and anatomical sequelae of bilateral motor cortex lesions in rats on postnatal days 1, 10, and in adulthood

Rats were given bilateral lesions of the motor cortex on the day of birth (P1), tenth day of life (P10), or in adulthood. They were trained on several motor tasks (skilled forelimb reaching, beam traversing, tongue extension), general motor activity, and a test of spatial learning (Morris water task). Although all lesion groups were impaired at skilled reaching, the P10 group was less impaired than either of the other two lesion groups. Furthermore, on the other motor tests the P10 group did not differ from controls whereas both P1 and adult groups were impaired. Only the P1 lesion group was impaired at the acquisition of the Morris water task. Anatomical analyses revealed that the P1 and P10 rats had smaller brains than the other two groups as well as having a generalized decrease in cortical thickness. Dendritic analysis of layer III pyramidal cells in the parietal cortex revealed a decrease in apical arbor in the lesion groups and an increase in the basilar arbor of the P1 and adult lesion animals. The P1 and adult operated groups showed an increase in spine density in the basilar dendrites of layer V pyramidal cells. Finally, analysis of the pattern of corticospinal projections revealed that the P1 animals had a markedly wider field of corticospinal projection neurons than any of the other groups. The widespread anatomical changes in all lesion groups versus the relatively better behavioral recovery after P10 lesions suggests that day 10 represents an optimal period for adapting to brain damage and subsequent brain reorganization.

The adolescent brain and age-related behavioral manifestations

To successfully negotiate the developmental transition between youth and adulthood, adolescents must maneuver this often stressful period while acquiring skills necessary for independence. Certain behavioral features, including age-related increases in social behavior and risk-taking/novelty-seeking, are common among adolescents of diverse mammalian species and may aid in this process. Reduced positive incentive values from stimuli may lead adolescents to pursue new appetitive reinforcers through drug use and other risk-taking behaviors, with their relative insensitivity to drugs supporting comparatively greater per occasion use. Pubertal increases in gonadal hormones are a hallmark of adolescence, although there is little evidence for a simple association of these hormones with behavioral change during adolescence. Prominent developmental transformations are seen in prefrontal cortex and limbic brain regions of adolescents across a variety of species, alterations that include an apparent shift in the balance between mesocortical and mesolimbic dopamine systems. Developmental changes in these stressor-sensitive regions, which are critical for attributing incentive salience to drugs and other stimuli, likely contribute to the unique characteristics of adolescence.

D-amphetamine-induced behavioral sensitization: implication of a glutamatergic medial prefrontal cortex-ventral tegmental area innervation

Behavioral sensitization to amphetamine is expressed as a progressive enhancement of the behavioral activating effects of the drug when repeated injections are performed as well as a long-lasting hypersensitivity to later environmental or pharmacological challenges. The mesoaccumbens dopamine system has been proposed to be the major candidate so far responsible for the induction and expression of this process, which are dependent on the action of amphetamine in the ventral tegmental area and nucleus accumbens, respectively. The development of this process has been proposed to be the result of an interaction between somatodendritically released dopamine and dopaminergic D1 receptors localized on different inputs to the ventral tegmental area, including glutamate afferents arising in part from mesocorticolimbic areas such as the medial prefrontal cortex and the amygdala. Three groups of experiments were designed to test the role of each of these components in the behavioral sensitization to amphetamine. First, the intervention of the glutamatergic transmission of the ventral tegmental area in the induction of sensitization to amphetamine was tested. The effects of an N-methyl-D-aspartate antagonist, 3-(R-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid. on the behavioral sensitization induced by amphetamine administered repeatedly in the ventral tegmental area was tested. It was found that the blockade of N-methyl-D-aspartate receptors with 3-(R-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid coadministered with amphetamine in the ventral tegmental area dose-dependently prevented the induction of sensitization. In a second step, the role of the structures which send glutamatergic inputs to the ventral tegmental area in the process of behavioral sensitization was tested. We evaluated the effects of ibotenic acid lesion of the medial prefrontal cortex and the amygdala on behavioral sensitization induced by peripheral or intra-ventral tegmental area administration of amphetamine. We found that ibotenic acid lesion of the medial prefrontal cortex blocked the behavioral sensitization induced by both intra-ventral tegmental area and peripheral treatment with amphetamine. In contrast, ibotenic acid lesion of the amygdala produced no effect on behavioral sensitization induced peripherally or centrally. These experiments confirmed (i) that the ventral tegmental area, where dopaminergic cell bodies are located, is a critical site for the induction of behavioral sensitization, (ii) that this process implicates the glutamatergic transmission in the ventral tegmental area, and (iii) that the medial prefrontal cortex is crucially implicated merely because of its direct glutamatergic inputs on to ventral tegmental area neurons. Together, these results reinforce the view that the behavioral sensitization to amphetamine implicates not only the mesoaccumbens dopaminergic neurons, but also other structures of the mesocorticolimbic system, such as the medial prefrontal cortex and more specifically its glutamatergic component.

Effects of excitotoxic lesions of the rat prefrontal cortex on CREB regulation and presynaptic markers of dopamine and amino acid function in the nucleus accumbens

The present study investigated the effects of excitotoxic lesions of the prefrontal cortex (PFC) on dopamine (DA) and excitatory amino acid (EAA) function in the nucleus accumbens core using in vivo microdialysis in freely moving rats. As a postsynaptic marker of neuronal function, the nuclear levels of the transcriptional factor CREB and its active phosphorylated form, CREB-P, were measured in the ventral tegmental area (VTA), and in the core and shell subregions of the nucleus accumbens of sham and lesioned animals. PFC-lesioned animals exhibited a greater locomotor response to novelty and amphetamine administration (125-500 microg/kg i.v.). No change was observed in extracellular levels of glutamate or saturable d-aspartate binding (a marker for the high-affinity EAA transporter) in the nucleus accumbens of PFC-lesioned animals. Extracellular levels of DA were comparable in sham and lesioned animals under tonic conditions, however, following amphetamine administration, DA efflux was significantly attenuated in lesioned animals. No correlation was observed between microdialysate levels of amino acids and the attenuated dopaminergic response to amphetamine in lesioned animals. Further, no effect of the lesion was found on nuclear CREB protein in saline- and amphetamine-treated rats. The density of CREB-P immunoreactive nuclei, while remaining unchanged in the VTA, increased in the nucleus accumbens shell following amphetamine treatment in lesioned animals. The results show that an important modulatory role of the PFC on the behavioural response to novelty and amphetamine is associated with the level of immediate-early gene regulation rather than levels of extracellular DA and amino acids in the ventral striatum.

An escalating dose "binge" model of amphetamine psychosis: behavioral and neurochemical characteristics

Stimulant-induced psychosis is most frequently associated with a chronic, high-dose, multiple daily ("binge") exposure pattern of stimulant abuse. To simulate these conditions, rats were exposed to escalating doses of amphetamine (Escalating Dose phase, 1.0-8.0 mg/kg) before multiple daily injections of relatively high doses of the drug (Run phase, 8.0 mg/kg/2 hr x 4 injections). Behavior was monitored continuously during the course of these treatments as well as during subsequent amphetamine challenges at various times after discontinuation of drug treatment. With the Escalating Dose-Run pattern of administration, a unique behavioral profile emerged in which tolerance occurred to the amount of time spent engaged in continuous focused stereotypy simultaneous with a profound increase in ambulatory activity that appeared agitated and disorganized. Parallel in vivo microdialysis studies showed progressively declining extracellular dopamine and serotonin responses, both within and between successive runs, whereas the norepinephrine response remained relatively unaltered. We propose that this model more closely resembles clinical manifestations of amphetamine psychosis and that the alterations may reflect a shift in the relative activation of mesolimbic and nigro-striatal dopamine pathways.

Cortical damage enhances pemoline-induced self-injurious behavior in prepubertal rats

Self-injurious behavior (SIB) is a devastating characteristic of several developmental disorders including a number of mental retardation syndromes. The functional neuroanatomy and neuropharmacology of SIB is not well understood. Self-biting behavior (SBB) can be induced in rats by a high dose, systemic injection of pemoline (250 mg/kg, SC). This animal model allows for the investigation of anatomical and pharmacological aspects of SIB. Cortical pathology is a common occurrence in human disorders with SIB, and may be a fundamental pathological factor in producing the behavior. The present experiment was designed to investigate the effects of cortical damage on pemoline-induced SBB in prepubertal rats. Bilateral cortical aspirations were performed in 3-5-week-old rats. One week postsurgery, a pemoline challenge was administered. Behavioral comparisons were completed between the lesion group and an anesthetized-only control group. Results indicated that cortical damage significantly enhanced pemoline-induced SBB, along with some of the other pemoline-induced stereotypical behaviors. These results support the hypothesis that cortical damage influences the expression of stimulant-induced self-injury, and potential mechanisms for this influence are suggested.

Delta9-tetrahydrocannabinol increases sequence-specific AP-1 DNA-binding activity and Fos-related antigens in the rat brain

Delta-9-tetrahydrocannabinol (delta9-THC), the psychoactive principle of marijuana, has been shown to upregulate the mRNA levels of immediate-early genes in the rat brain. Using electrophoretic mobility-shift assay and one-dimensional Western blot, we here report that delta9-THC increases Activator protein-1 (AP-1) DNA-binding and Fos-related antigen activity in discrete areas of the rat brain. One hour after the intraperitoneal administration of delta9-THC at a dose of 10 or 15 mg/kg, AP-1 DNA-binding activity in the nucleus accumbens increased by 33 and 49%, respectively, while Western blot showed an increase in both c-Fos, FosB, Fra-1 (Fos-related antigen) and Fra-2. In the cingulate cortex and caudate-putamen, delta9-THC significantly increased AP-1 DNA-binding activity only at the highest dose used (57 and 71%, respectively). While in the caudate-putamen the increase in AP-1 DNA binding was mainly due to an elevation of the c-Fos and FosB proteins, the same phenomenon depended on the FosB, Fra-1 and Fra-2 peptides in the cingulate cortex. The effect of delta9-THC on the AP-1 DNA binding and the Fos-related antigens in the nucleus accumbens was blocked by the specific cannabinoid antagonist SR141716 A (3 mg/kg i.p.). delta9-THC failed to modify Specificity protein 1 (Sp1) DNA-binding activity. The results indicate that delta9-THC activates gene coding for AP-1 DNA-binding proteins by acting on cannabinoid receptors, and induces a different transcriptional program on the early-immediate gene of the Fos family, in different areas in the rat brain, suggesting that this mechanism might be involved in the central actions of cannabinoids.

Mesolimbic dopaminergic mechanisms underlying individual differences in sugar consumption and amphetamine hyperlocomotion in Wistar rats

Individual differences within strains of rats have been demonstrated for dopamine-mediated behaviours and responses to dopaminergic drugs. Differences in mesolimbic dopamine function may underlie individual differences in some of these behaviours, including sugar consumption and amphetamine hyperlocomotion. The present study addressed two potential mechanisms for these differences in dopamine-mediated behaviours. The possibility of functional differences in dopamine receptor subtypes was tested in LOW and HIGH sugar feeders. LOW and HIGH feeders did not differ in their response to the partial D1 agonist SKF-38393. The highest dose (2.5 mg/kg) of the D2 agonist quinpirole stimulated locomotor activity to a greater degree in a subset of HIGH sugar feeders as compared with LOW feeders. All doses of amphetamine induced a greater locomotor response in HIGH feeders as compared with LOW feeders, and HIGH feeders exhibited higher levels of extracellular dopamine in the nucleus accumbens than LOW feeders following exposure to sugar and treatment with amphetamine. These results support the interpretation that LOW and HIGH feeders exhibit differences in presynaptic nucleus accumbens dopamine function that account for the expression of individual differences in sugar consumption and response to amphetamine treatments. A subset of HIGH feeders may also exhibit greater D2 receptor function.

Cerebral morphology and functional sparing after prenatal frontal cortex lesions in rats

Rats were given suction lesions of the presumptive frontal cortex on embryonic day 18 (E18) and subsequently tested, as adults, on tests of spatial navigation (Morris water task, radial arm maze), motor tasks (Whishaw reaching task, beam walking), and locomotor activity. Frontal cortical lesions at E18 affected cerebral morphogenesis, producing unusual morphological structures including abnormal patches of neurons in the cortex and white matter as well as neuronal bridges between the hemispheres. A small sample of E18 operates also had hydrocephaly. The animals with E18 lesions without hydrocephalus were behaviorally indistinguishable from littermate controls. The results demonstrate that animals with focal lesions of the presumptive frontal cortex have gross abnormalities in cerebral morphology but the lesions leave the functions normally subserved by the frontal cortex in adult rats unaffected. The results are discussed in the context of a hypothesis regarding the optimal times for functional recovery from cortical injury.

Contrasting effects of excitotoxic lesions of the prefrontal cortex on the behavioural response to D-amphetamine and presynaptic and postsynaptic measures of striatal dopamine function in monkeys

The effects of excitotoxic lesions of the prefrontal cortex on behavioural, neurochemical and molecular indices of dopamine function in the caudate nucleus were studied in the marmoset. The lesion, which encompassed both the lateral and orbital regions of prefrontal cortex, made the animals more sensitive to the performance disrupting effects of the dopamine releasing drug, D-amphetamine, in a variation of the object retrieval task. Specifically, following drug administration, the lesioned marmosets were less able to gain access to food reward in the minimum number of responses. Analysis of the nature of the errors suggested that the deficit was not due to inhibition of a prepotent response as the lesioned monkeys were just as likely to make a detour reach to the unopened side of the box as a direct "line-of-sight" reach into the unopened front of the box. Rather, the data indicated a general disorganization of behaviour. The enhanced behavioural responsiveness to manipulations increasing presynaptic dopamine function was accompanied by neurochemical changes indicating a reduced responsiveness, as revealed by in vivo microdialysis. Thus, in lesioned animals, whilst there were no effects on baseline levels of extracellular dopamine in dorsolateral caudate, evoked release, both to systemic D-amphetamine and to a local depolarizing pulse of potassium ions, was attenuated. These opposite effects of the prefrontal cortex lesion on behavioural and neurochemical indices of striatal dopamine function occurred in the absence of any changes in striatal dopamine receptors of the D1 and D2 subtype, as determined both by radioligand binding assays and measurements of messenger RNA using in situ hydridization techniques. These data provide further insight into the interactions between prefrontal cortex and striatal dopamine function in the non-human primate. In particular, when taken in the light of our previous studies they indicate that following prefrontal manipulations, concurrence between behavioural and neurochemical indices of striatal dopamine function depends, critically, on the behavioural task. These findings are discussed with respect to the growing body of evidence implicating abnormalities in frontostriatal neurotransmission in complex disorders such as schizophrenia.

I. Serotonin (5-HT) within dopamine reward circuits signals open-field behavior. II. Basis for 5-HT--DA interaction in cocaine dysfunctional behavior

Light microscopic immunocytochemical studies, using a sensitive silver intensification procedure, show that dopamine (DA) and serotonin (5-HT) axons terminate on neurons in the nucleus accumbens (NAcc) (A10) terminals and also in dorsal striatum (DSTr) (A9) terminals. The data demonstrate a prominent endogenous anatomic interaction at these distal presynaptic sites between the neurotransmitters 5-HT and DA; the pattern of the 5-HT-DA interaction differs between A10 and A9 terminals. Moreover, in distinction to the variance shown anatomically between 5-HT--DA interactions at distal A9 and A10 sites, the 5-HT--DA interactions at the level of DA somatodendrites, the proximal site, are similar, i.e. 5-HT terminals in the midbrain tegmentum are profuse and have a massive overlap with DA neurons in both ventral tegmental area (VTA) and substantia nigra pars compacta (SNpc). We suggest with reference to the DA neurons of A10 and A9 pathways, inclusive of somatodendrites (sites of proximal presynaptic interactions in the midbrain) and axons (sites of distal presynaptic interactions), that 5-HT--DA interactions in A10 terminals are more likely to exceed those in the DStr arrangement. Furthermore, our neuroanatomic data show that axonally released DA at A10 terminals may originate from proximal 5-HT somatodendrites, i.e. dorsal raphe (DR) or the proximal DA somatodendrites, VTA. In vivo microvoltammetric studies were done with highly sensitive temporal and spatial resolution; the studies demonstrate basal (endogenous) real time 5-HT release at distal A10 and distal A9 terminal fields and real time 5-HT release at proximal A10 VTA somatodendrites. In vivo microvoltammetric studies were performed concurrently and on line with studies of DA release, also at distal A10 and distal A9 terminal fields and at proximal A10 somatodendrites. Serotonin release was detected in a separate voltammetric peak from the DA voltammetric peak. The electrochemical signal for 5-HT release was detected within 10-12 s and that for DA release within 12-15 s, after each biogenic amine diffused through the synaptic environment onto the microelectrode surface. The electrochemical signal for 5-HT and a separate electrochemical signal for DA are detected on the same voltammogram within 22-27 s; each electrochemical signal represents current changes in picoamperes, within seconds of detection time. The amplitude of each electrochemical signal reflects the changes in diffusion of each biogenic amine to the microelectrode surface. Each neurotransmitter has a distinct potential at which oxidation occurs; this results in a recording which has a distinct peak for a specific neurotransmitter. The concentration of each neurotransmitter within the synaptic environment is directly related to the electrochemical signal detected via the Cottrell equation. Voltammograms were recorded every 5 min. At the time that basal 5-HT release and basal DA release were recorded within same animal control, open-field behavioral studies were performed, also concurrently, by infrared photocell beams. The frequency of each behavioral parameter was monitored every 100 ms; the number of behavioral events, were summated every 5 min during the time course of study. Thus, the detection of neurotransmitters occurs in real time, while simultaneously monitoring the animal's behavior by infrared photocell beams. The results from the in vivo microvoltammetric and behavioral data from this study show that basal 5-HT release at distal A10 and A9 terminals dramatically increased with DA release. Moreover, each increase in basal 5-HT release, at both A10 and at A9 terminal fields occurred consistently and at the same time as each increase in open-field locomotion and stereotypy occurred naturally during the animal's exploration in a novel chamber. Thus, the terminology 'synchronous and simultaneous' describes aptly the correlation between 5-HT release at distal A10 and A9 terminal fields and open-field locomo

The effects of limbic lesions on locomotion and stereotypy elicited by dopamine agonists in the rat

The purpose of this experiment was to investigate the functional contributions of various limbic structures to locomotion and stereotypy induced by dopaminergic drugs. Female rats were randomly assigned to one of 5 groups (n = 10-14 rats/group) that received either a lesion of the hippocampus (colchicine + kainic acid), basolateral amygdala (quinolinic acid), frontal cortex (aspiration), nucleus accumbens (ibotenic acid), or served as unoperated controls. Beginning at least 2 weeks following surgery locomotion (measured as photocell beam breaks) elicited by D-amphetamine (0.0, 0.32, 1.0 and 3.2 mg/kg), SKF 82958 (0.0, 0.04, 0.08 and 0.16 mg/kg) or quinpirole (0.0, 0.25, 0.1 and 0.5 mg/kg) was determined. In agreement with previous results rats with hippocampal lesions were hyperactive in response to amphetamine. In comparison to these changes in drug-induced locomotion, lesions of the basolateral amygdala, and frontal cortex had only minor effects on drug-induced locomotion. Lesions of the nucleus accumbens produced consistent hyperactivity that was suppressed by doses of amphetamine or quinpirole that elicited behavioral stereotypy. These results provide evidence suggesting that, in comparison to other limbic structures that have substantial inputs to the nucleus accumbens, the hippocampus play a relatively prominent role in the modulation of drug-induced locomotion.

Dopaminergic function in the neostriatum and nucleus accumbens of young and aged Fischer 344 rats

Age-dependent alterations in behavioral and neuronal functioning were assessed in young (2-3 month), middle-aged (12 month), and aged (24 month) Fischer 344 rats treated with the indirect dopamine agonist amphetamine (2.25 or 5 mg/kg), the D1 agonist SKF 38393 (7.5, 15, 30 mg/kg), or the D2 agonist quinpirole (0.3, 1.0, 3.0 mg/kg). Drug-induced changes in activity and stereotypy were measured during a 90-min testing session, with Fos immunohistochemistry being used to assess the neuronal response to dopamine agonist treatment. As expected, aged rats given amphetamine (5 mg/kg) had fewer activity counts and higher stereotypy scores than young rats. Middle-aged rats also had fewer activity counts but were similar in stereotypy scores to young rats. Amphetamine also induced different patterns of Fos immunoreactivity in the neostriatum and nucleus accumbens of young and aged rats, as Fos expression in aged rats exhibited a distinctive dorsal to ventral pattern of decline. In general, SKF 38393 had few age-related actions, although aged rats did show a slight relative increase in stereotypy. In contrast, the D2 agonist quinpirole substantially enhanced the motor activity and Fos expression of young rats, while only modestly affecting aged rats. Hence, these results suggest that the D2 receptor is more vulnerable to the effects of aging than the D1 receptor.

The nature of interactions involving prefrontal and striatal dopamine systems

A number of converging lines of evidence from work in rodents suggest that dopamine (DA) function in the prefrontal cortex (PFC) and striatal terminal fields may be linked, possibly in an 'inverse' manner, whereby a change in prefrontal dopamine transmission in one direction occasions an opposite change in dopamine function in striatal territories. The present article considers the possible functional importance of this concept in the light of recent neuroanatomical data and new data from our own laboratory indicating that, at the neurochemical level, the basic finding of an inverse relationship between dopamine function in prefrontal and striatal regions also holds good in the non-human primate. The main conclusion is that the simple idea of an inverse relationship between prefrontal and striatal dopamine systems emphasizing presynaptic release mechanisms is unlikely to underlie, solely, the full repertoire of functional interactions. Whilst there is evidence consistent with dynamic interactions between prefrontal and striatal dopamine release under some circumstances, specifically, during the early phases of aversive learning, a complete account of possible interactions between prefrontal and striatal dopamine systems requires consideration of additional factors. Such factors include: (1) the precise nature of the psychological function investigated, (2) the possibility of acute, localized changes in striatal postsynaptic function secondary to changes in presynaptic function and (3) the possibility of manipulations of prefrontal cortex leading to adaptive changes in striatal function, at a diffuse, neural systems level.

Changes in behavior and monoamine levels in microdialysate from dorsal striatum after 6-OHDA infusions into ventral striatum

Long-Evans rats received bilateral 6-hydroxydopamine infusions into the nucleus accumbens and were tested immediately (1 and 2 days) or after a recovery period (14 and 15 days) for changes in extracellular levels of dorsal striatal monoamines using in vivo microdialysis. Compared to controls, the monoamine metabolites 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindoleacetic acid were generally enhanced when tested immediately after 6-hydroxydopamine treatment, including spontaneous levels and those following depolarizing infusions of potassium (60 mM, 20 min) through the microdialysis probes. Following 2 weeks recovery, dopamine metabolite levels were depressed and the serotonin metabolite levels remained enhanced. D-Amphetamine sulfate (1.5 mg/kg, SC) stimulated dopamine overflow was enhanced 2 days after 6-hydroxydopamine administration, but not after 2 weeks recovery. In contrast, potassium increased dopamine overflow to the same extent as control animals regardless of recovery period following 6-hydroxydopamine. The immediate changes in striatal monoamine activity were accompanied by a potentiation of amphetamine-induced stereotyped behaviors. We suggest that transient presynaptic changes within the dorsal striatum following disruption of the ventral striatum may mediate some general aspects of loss and recovery of behavior related to the time course of 6-hydroxydopamine neurotoxicity.

Locating reward cue at response manipulandum (CAM) induces symptoms of drug abuse

Appetitive instrumental discrimination learning procedures provide for CAM (cue and manipulandum) when the reward cue (discriminative stimulus positively correlated with positive reinforcement) is located at the response manipulandum (object that when contacted or manipulated defines the performance of the instrumental response). Evidence reviewed shows that CAM induces excessive and compulsive instrumental responding relative to otherwise comparable non-CAM control procedures. In humans, symptoms of drug abuse are particularly likely when the drug-taking implement (response manipulandum at which instrumental drug-taking is directed) is also predictive of the drug's rewarding effects (reward cue). Evidence that the predictive relationship between a drug-taking implement and drug reward relates to drug abuse is reviewed, and implications for treatment and prevention are considered. CAM is related to neurobiological models of drug abuse that emphasize the role of the neurotransmitter dopamine (DA). CAM produces convergence of DA-mediated responding for conditioned reinforcement with DA mediation of psychomotor activation and incentive-motivational processes to yield reflexive cue-directed responding not observed in non-CAM controls.

Competitive NMDA receptor antagonists do not produce locomotor hyperactivity by a dopamine-dependent mechanism

The involvement of dopaminergic activity in the mediation of the behavioural effects produced by blockade of NMDA receptors in the nucleus accumbens was investigated. Intra-accumbens infusion of the competitive NMDA receptor antagonist, DL-2-amino-5-phosphonovaleric acid (AP-5) (2, 4 and 10 micrograms/0.5 microliters) induced a dose-dependent increase in locomotor activity in rats. Pharmacological blockade of dopamine receptors locally in the nucleus accumbens with haloperidol (5 micrograms/microliters) failed to reduce the locomotor effects of AP-5 (10 micrograms), but antagonized the effects induced by the non-competitive NMDA receptor antagonist, MK-801 ((+)-5-methyl-10,11-dihydro(a,d)-cyclohepten-5,10-imine hydrogen maleate salt) (10 micrograms). The effects of dopamine co-administered with AP-5 at various doses in the nucleus accumbens were also examined. When the level of locomotor activity induced by AP-5 (10 micrograms) was similar to that produced by dopamine (10 micrograms), the simultaneous infusion of both compounds at this dose did not increase or decrease the locomotor response. When the level of locomotor activity induced by AP-5 (10 or 4 micrograms) was lower than that produced by a higher dose of dopamine (20 micrograms), the combined infusion of both compounds resulted in a locomotor response similar to that induced by AP-5 alone, indicating a reduction of dopamine locomotor effects. These results show that the locomotor hyperactivity induced by AP-5 was not modified when the dopaminergic activity in the nucleus accumbens was either reduced or enhanced, suggesting that the behavioural effects resulting from the blockade of NMDA receptors with the competitive NMDA receptor antagonist, AP-5, is not mediated by endogenous dopamine in this brain area.

Central nervous stimulants facilitate sexual behavior in male rats with medial prefrontal cortex lesions

Male rats with lesions of the cerebral cortex near the midline in the frontal region destroying most of the cingulate cortex and producing some damage to adjacent frontal areas have very long mount and intromission latencies. Otherwise their sexual behavior is essentially normal. The dopamine releasers amfonelic acid, 0.5 mg/kg, and amphetamine, 1 mg/kg, reduced the mount and intromission latencies in males with such lesions. Caffeine, 30 mg/kg, had similar effects. None of the drugs modified sexual behavior in intact males. It has been suggested that medial prefrontal lesions reduce the animal's reactivity to environmental stimuli, and hence renders the activation of sexual behavior difficult. Present results show that stimulant drugs are capable of compensating for this reduced reactivity. The possible mechanisms behind this effect are discussed. The lesion had also a small but consistent effect on the intromission ratio, suggesting some motor impairment. The effect on intromission ratio was not reduced by the drugs, suggesting that the lesion's motor consequences are mediated by mechanisms different from those controlling behavioral reactivity. The noradrenaline precursor dl-threo-dihydroxyphenylserine, 10 mg/kg, in combination with carbidopa, 50 mg/kg, increased mount and intromission latencies in both intact and lesioned males. Thus, activation of noradrenergic neurotransmission had effects opposite to those found after activation of dopaminergic transmission. Noradrenergic stimulation cannot, therefore, be important for the effects of amphetamine or amfonelic acid.

Prefrontal cortical and hippocampal modulation of haloperidol-induced catalepsy and apomorphine-induced stereotypic behaviors in the rat

Effects of prefrontal cortical or hippocampal excitotoxic lesions on behavioral parameters related to dopaminergic transmission in the basal ganglia were investigated in the rat. We examined haloperidol-induced catalepsy and apomorphine-induced stereotypic behaviors after ibotenic acid lesions of the medial prefrontal cortex (MPFC), dorsal (DH), or ventral hippocampus (VH) in adult rats. Haloperidol-induced (1 mg/kg) catalepsy was decreased in rats with either MPFC or VH but not DH lesions. While both DH and VH lesioned animals demonstrated a reduction in apomorphine-induced (0.75 mg/kg) stereotypic behaviors, the VH lesioned animals also showed an enhancement of locomotor activity. MPFC lesioned rats tended towards potentiation of stereotypic behaviors and reduced locomotion after apomorphine administration. These data indicate that loss of prefrontal cortical or hippocampal modulation leads to an enhancement of DA transmission within the basal ganglia, though the pattern of augmentation depends on the area lesioned.

Effects of selective dopamine depletion in medial prefrontal cortex on basal and evoked extracellular dopamine in neostriatum

In this study, we demonstrate that 6-hydroxydopamine (6-OHDA) can be used to produce a lesion of dopamine (DA) terminals in medial prefrontal cortex (mPFC) while sparing the noradrenergic innervation in this region. Furthermore, we determined the impact of these lesions on both extracellular DA in neostriatum, using in vivo microdialysis, and locomotor activity. Our results demonstrate that, whereas higher doses of 6-OHDA (> or = 4 micrograms) depleted both DA and norepinephrine (NE) in mPFC, 1 micrograms 6-OHDA produced a depletion of DA (-79%) without significantly affecting NE content (-13%). Selective depletion of DA content in mPFC did not alter basal levels of extracellular DA in neostriatum determined 14 days after the lesion. The lesion also did not alter the ability of acute tail pressure (30 min) to increase extracellular DA in neostriatum or to stimulate locomotor activity. Depletion of DA in mPFC did not alter the ability of d-amphetamine (1.5 mg/kg, i.p.) to increase intracellular DA in neostriatum. In contrast, the maximum amphetamine-induced increase in locomotor activity was attenuated in lesioned rats as compared with control rats (670 and 280 locomotor counts/15 min, respectively). These data suggest that in the intact system, DA terminals in mPFC do not regulate extracellular DA in neostriatum. In addition, these data confirm that DA terminals in mPFC can influence stimulant-induced locomotion.

Light microscopic immunocytochemical evidence of converging serotonin and dopamine terminals in ventrolateral nucleus accumbens

The mesencephalic tegmentum contains monoaminergic neurons that project to the nucleus accumbens (NAcc). These monoaminergic neurons consist of the serotonergic (5-HT) neurons of the dorsal and median raphe and the dopaminergic (DA) neurons of the ventral tegmental area (VTA). Recent neurochemical reports describe cocaine-induced alterations in dopamine and serotonin release in NAcc that has coincidental occurrence both spatially and temporally, as shown by in vivo voltammetry. There is a functional role for 5-HT-DA interactions within the NAcc in the underlying mechanism of action of cocaine as well as for 5-HT in A10 DA neurons in the basal or endogenous state whether or not cocaine-relevant reward circuits are involved. Our objective was to study the neuroanatomic localization of tyrosine hydroxylase-containing (TH) and 5-HT-containing axons in the ventrolateral region of the rat NAcc, where codetection of monoamines had been assessed. The significance of this vINAcc is its reciprocal connectivity with VTA, which contains the somatodendritic portions of the mesoacumbens DA neurons. The results showed that, in the vINAcc, the core contained a dense terminal field of TH axons that had an extensive overlap with 5-HT axons in the periphery within the core. Because the in vivo electrochemical codetection of DA and 5-HT assessed in the ventral-most aspect of this overlap zone can be correlated with terminal release, a functional interaction of 5-HT and DA at postsynaptic sites in vINAcc is possible.

"Short-stops" in rats with fimbria-fornix lesions: evidence for change in the mobility gradient

Rats with damage to the hippocampal formation and allied structures are hyperactive in many test situations but the cause of this hyperactivity is not known. Here the activity of control rats and rats with fimbria-fornix lesions is documented in tests of overnight activity. Details of activity are then characterized from video recordings of behavior in an open field. Rats with fimbria-fornix lesions make significantly more stops of shorter duration and thus more individual trips than control rats but they do not differ in the distance traveled on individual trips or in travel speed. It is suggested that the main difference between fimbria-fornix rats and control rats is that when fimbria-fornix rats stop they remain "still" for shorter durations than do control rats. This finding is discussed in relation to a theory of locomotor/exploratory behavior, and in relation to its implications with respect to the performance of fimbria-fornix rats in studies of learning and memory.

Effects of D-cycloserine and (+)-HA-966 on the locomotor stimulation induced by NMDA antagonists and clonidine in monoamine-depleted mice

We have previously observed that an N-methyl-D-aspartate (NMDA) antagonist in combination with the alpha 2-adrenoceptor agonist clonidine produces a marked locomotor stimulation in monoamine-depleted mice. In this paper we report on how the partial glycine agonists D-cycloserine (high intrinsic activity) and (+)-HA-966 [(+)-3-amino-1-hydroxypyrrolid-2-one; low intrinsic activity] affect this response; the interaction with both an uncompetitive and a competitive NMDA antagonist was investigated. (+)-HA-966 was found to counteract the locomotor stimulation produced by clonidine combined with either an uncompetitive (MK-801 = dizocilpine) or a competitive [D-CPPene = 3-(2-carboxypiperazine-4-yl)-1-propenyl-1-phosphonic acid] NMDA antagonist. D-cycloserine potentiated the locomotor stimulation produced by either NMDA antagonist combined with clonidine, although statistical significance was achieved only in the case of MK-801. If the present hyperactivity model has any relevance for psychosis the prediction based on the present results would be that d-cycloserine, contrary to current hopes, might not be so effective in schizophrenia, whereas (+)-HA-966 might be an interesting candidate.

Individual differences in sugar intake predict the locomotor response to acute and repeated amphetamine administration

Rats exhibit profound individual differences in their propensity to ingest sugar and in their locomotor response to AMP. Intrinsic variation in the responsiveness of mesolimbic dopamine mechanisms has been suggested to account for these individual differences. In light of this overlap, it might be expected that individual differences in one behavior would predict individual differences in the other. The present study determined whether individual differences in sugar intake would predict individual differences in the locomotor response to AMP. Male Wistar rats were divided into low and high feeders based on a median split of their sugar intake in response to saline administration and were subsequently tested for their locomotor response to either 1.0 or 1.75 mg/kg AMP in experiment 1. High sugar feeders exhibited significantly more locomotion than low sugar feeders in response to 1.75 mg/kg AMP. This difference was observed immediately after injection and continued for approximately 90 min. There was no difference between the two groups in their locomotor response to 1.0 mg/kg AMP. In experiment 2, rats receiving 1.0 mg/kg AMP in experiment 1 were tested for the development of behavioral sensitization with repeated AMP administrations. Rats were administered 1.0 mg/kg AMP across 5 test days, interspersed with days in which they received AMP treatment in their home cages to minimize conditioning effects. High sugar feeders exhibited greater behavioral sensitization than low sugar feeders with repeated AMP administration. Starting on test day 3, high sugar feeders exhibited significantly greater AMP-induced locomotor activity than low sugar feeders.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of combined prefrontal cortical and hippocampal damage on dopamine-related behaviors in rats

The effects of excitotoxic damage to both the medial prefrontal cortex (MPFC) and the ventral hippocampus (VH) on behaviors related to mesolimbic/nigrostriatal dopamine (DA) transmission were investigated in the rat. Locomotor activity in a novel environment, after injection of saline, and after d-amphetamine was assessed 2 and 4 weeks after ibotenic acid lesion of both MPFC and VH in adult rats. In addition, stereotypic behaviors and locomotion after apomorphine were evaluated 8 weeks after the lesion. Locomotor activity was significantly enhanced in all testing conditions in lesioned rats as compared with sham-operated animals, while oral stereotypic behaviors elicited by apomorphine were attenuated possibly because they were eclipsed by excessive locomotion. These data indicate that coexisting lesions of the MPFC and VH in adult rats produce potent and long-lasting effects on behaviors believed to be dependent primarily on the mesolimbic DA system. The profile of changes resembles more closely that observed after excitotoxic lesions of the VH alone rather than that after separate MPFC lesion.

Consequences of cerebellar lesions at early and later ages: clinical relevance of animal experiments

Animal experiments demonstrated that reactions of the brain after early lesions differ from those after lesions at adult age. Detailed knowledge on the neuroanatomical and neurophysiological consequences of brain lesions was obtained in humans and will be gained from lesion experiments in animals. Prerequisites for extrapolating animal data to the clinical situation are discussed: knowledge on the maturational stage at which the lesion occurs and the behavioral expression of the damaged neural system. The extensive remodelling after early unilateral cerebellar hemispherectomy and its consequences for behavioural development in the rat are presented and discussed.