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

A 'single toxin-double lesion' rat model of striatonigral degeneration by intrastriatal 1-methyl-4-phenylpyridinium ion injection: a motor behavioural analysis

Previous attempts to reproduce striatonigral degeneration, the core pathology underlying Parkinsonism in multiple system atrophy, have been impeded by interactions in the neurotoxins used to replicate striatal and nigral degeneration in rodents. To overcome these interactions, we have developed a new model of striatonigral degeneration which uses a single unilateral administration of 1-methyl-4-phenylpyridinium ion (MPP(+)) into the rat striatum. Spontaneous and drug-induced rotational behaviour, thigmotactic scanning, stepping adjusting steps and paw reaching deficits were compared in four groups of animals: group 1 (control), group 2 (20 microg quinolinic acid), group 3 (20 microg 6-hydroxydopamine), and group 4 (90 nmol MPP(+)). MPP(+) administration resulted in the absence of the amphetamine-induced ipsilateral bias observed in the 6-hydroxydopamine group and of the apomorphine-induced ipsilateral bias observed in the quinolinic acid group. There was no thigmotactic scanning asymmetry in the MPP(+)-injected rats compared to the quinolinic acid- and the 6-hydroxydopamine-injected rats. MPP(+) elicited a bilateral stepping adjustment deficit similar to that found in the quinolinic acid group when compared to controls. MPP(+) also elicited a more severe and significant contralateral deficit in paw reaching compared to controls, 6-hydroxydopamine and quinolinic acid groups. Histopathology revealed a significant reduction of the lesioned striatal surface (-47.53%) with neuronal loss and increased astrogliosis in the MPP(+) group grossly similar to that found in the quinolinic acid group. Contrary to the latter group, however, loss of intrastriatal and striatal-crossing fibre bundles was observed in the MPP(+) group as there was also some retrograde degeneration in the ipsilateral thalamic parafascicular nucleus. The mean loss of dopaminergic cells in the ipsilateral substantia nigra pars compacta in MPP(+) rats was less marked (-48.8%) than in the 6-hydroxydopamine rats (-63.6%) and was not significant in quinolinic acid rats (-5.2%). This study shows that a single unilateral intrastriatal administration of MPP(+) induces a unique motor behaviour resulting from both nigral and striatal degeneration, but also from possible extrastriatal damage. This 'single toxin-double lesion' paradigm may thus serve as a rat model of striatonigral degeneration.

Effects of light deprivation on recovery from neglect and extinction induced by unilateral lesions of the medial agranular cortex and dorsocentral striatum

A number of previous studies have indicated that an environmental manipulation, 48 h of light deprivation (LD), produces virtually complete and permanent behavioral recovery of function from neglect induced by medial agranular cortex (AGm) lesions. LD-induced behavioral recovery from neglect is correlated with physiological changes in the dorsolateral striatum, an area that contains the projection zone of AGm efferents in the dorsocentral striatum (DCS). In this study, the behavioral effects of 48 h of LD on subjects with either unilateral DCS, AGm, or combined AGm/DCS lesions were investigated to examine whether the integrity of the DCS is crucial for behavioral recovery from neglect and whether LD will have a therapeutic effect on extinction deficits. Subjects were tested for extinction to bilateral simultaneous stimulation of the forepaws, and visual, auditory and tactile neglect. Forty-eight hours of LD failed to produce behavioral recovery from neglect in rats with DCS lesions, or a therapeutic affect on extinction deficits in any of the groups. The results of this study further support the crucial role of the DCS in recovery from neglect induced by AGm lesions and suggests that the DCS may be the crucial site for the mechanisms leading to LD-induced recovery. Further, the ineffectiveness of LD on extinction suggests that components of the neglect syndrome are dissociable and may require different therapeutic interventions.

Nigrothalamostriatal and nigrothalamocortical pathways via the ventrolateral parafascicular nucleus

The present tract-tracing study in the rat indicated that neurons in the ventrolateral part of the parafascicular thalamic nucleus (PF), where nigral fibers from the dorsolateral part of the substantia nigra pars reticulata (SNr) terminated, sent their axons to the ventrolateral part of the striatum as well as to the rostrolateral part of the lateral agranular cortex (AGl). We further demonstrated that symmetrical synaptic contacts were made between these nigral axons and striatum- or AGl-projecting PF neurons. Since the dorsolateral part of the SNr, ventrolateral part of the striatum and rostrolateral part of the AGl are responsible regions for orofacial behaviors, the nigrothalamostriatal and nigrothalamo-cortical pathways via the ventrolateral part of the PF may play a role in the control of orofacial motor function.

Lesion of subthalamic or motor thalamic nucleus in 6-hydroxydopamine-treated rats: Effects on striatal glutamate and apomorphine-induced contralateral rotations

A unilateral lesion of the rat nigrostriatal pathway with 6-hydroxydopamine (6-OHDA) results in a decrease in the basal extracellular level of striatal glutamate, a nearly complete loss of tyrosine hydroxylase (TH) immunolabeling, an increase in the density of glutamate immunogold labeling within nerve terminals making an asymmetrical synaptic contact, and an increase in the number of apomorphine-induced contralateral rotations. [Meshul et al. (1999) Neuroscience 88:1-16; Meshul and Allen (2000) Synapse 36:129-142]. In Parkinson's disease, a lesion of either the subthalamic nucleus (STN) or the motor thalamic nucleus relieves the patient of some of the motor difficulties associated with this disorder. In this rodent model, either the STN or motor thalamic nucleus was electrolytically destroyed 2 months following a unilateral 6-OHDA lesions. Following a lesion of either the STN or motor thalamic nucleus in 6-OHDA-treated rats, there was a significant decrease (40-60%) in the number of apomorphine-induced contralateral rotations compared to the 6-OHDA group. There was a significant decrease (<30%) in the basal extracellular level of striatal glutamate in all of the experimental groups compared to the sham group. Following an STN and/or 6-OHDA lesion, the decrease in striatal extracellular levels was inversely associated with an increase in the density of nerve terminal glutamate immunolabeling. There was no change in nerve terminal glutamate immunogold labeling in either the motor thalamic or motor thalamic plus 6-OHDA lesion groups compared to the sham group. The decrease in the number of apomorphine-induced rotations was not due to an increase in TH immunolabeling (i.e., sprouting) within the denervated striatum. This suggests that alterations in striatal glutamate appear not to be directly involved in the STN or motor thalamic lesion-induced reduction in contralateral rotations.

The hallucinogen d-lysergic acid diethylamide (d-LSD) induces the immediate-early gene c-Fos in rat forebrain

The hallucinogen d-lysergic acid diethylamide (d-LSD) evokes dramatic somatic and psychological effects. In order to analyze the neural activation induced by this unique psychoactive drug, we tested the hypothesis that expression of the immediate-early gene product c-Fos is induced in specific regions of the rat forebrain by a relatively low, behaviorally active, dose of d-LSD (0.16 mg/kg, i.p.); c-Fos protein expression was assessed at 30 min, and 1, 2 and 4 h following d-LSD injection. A time- and region-dependent expression of c-Fos was observed with a significant increase (P<0.05) in the number of c-Fos-positive cells detected in the anterior cingulate cortex at 1 h, the shell of the nucleus accumbens at 1 and 2 h, the bed nucleus of stria terminalis lateral at 2 h and the paraventricular hypothalamic nucleus at 1, 2 and 4 h following systemic d-LSD administration. These data demonstrate a unique pattern of c-Fos expression in the rat forebrain following a relatively low dose of d-LSD and suggest that activation of these forebrain regions contributes to the unique behavioral effects of d-LSD.

Dopamine gating of glutamatergic sensorimotor and incentive motivational input signals to the striatum

Dopamine (DA) neurons of the substantia nigra (SN) and ventral tegmental area (VTA) respond to a wide category of salient stimuli. Activation of SN and VTA DA neurons, and consequent release of nigrostriatal and mesolimbic DA, modulates the processing of concurrent glutamate inputs to dorsal and ventral striatal target regions. According to the view described here, this occurs under conditions of unexpected environmental change regardless of whether that change is rewarding or aversive. Nigrostriatal and mesolimbic DA activity gates the input of sensory, motor, and incentive motivational (e.g. reward) signals to the striatum. In light of recent single-unit and brain imaging data, it is suggested that the striatal reward signals originate in the orbitofrontal cortex and basolateral amygdala (BLA), regions that project strongly to the striatum. A DA signal of salient unexpected event occurrence, from this framework, gates the throughput of the orbitofrontal glutamate reward input to the striatum just as it gates the throughput of corticostriatal sensory and motor signals needed for normal response execution. Processing of these incoming signals is enhanced when synaptic DA levels are high, because DA enhances the synaptic efficacy of strong concurrent glutamate inputs while reducing the efficacy of weak glutamate inputs. The impairments in motor performance and incentive motivational processes that follow from nigrostriatal and mesolimbic DA loss can be understood in terms of a single mechanism: abnormal processing of sensorimotor and incentive motivation-related glutamate input signals to the striatum.

Motivational views of reinforcement: implications for understanding the behavioral functions of nucleus accumbens dopamine

Although the Skinnerian 'Empirical Law of Effect' does not directly consider the fundamental properties of stimuli that enable them to act as reinforcers, such considerations are critical for determining if nucleus accumbens dopamine systems mediate reinforcement processes. Researchers who have attempted to identify the critical characteristics of reinforcing stimuli or activities have generally arrived at an emphasis upon motivational factors. A thorough review of the behavioral literature indicates that, across several different investigators offering a multitude of theoretical approaches, motivation is seen by many as being fundamental to the process of reinforcement. The reinforcer has been described as a goal, a commodity, an incentive, or a stimulus that is being approached, self-administered, attained or preserved. Reinforcers also have been described as activities that are preferred, deprived or in some way being regulated. It is evident that this 'motivational' or 'regulatory' view of reinforcement has had enormous influence over the hypothesis that DA directly mediates 'reward' or 'reinforcement' processes. Indeed, proponents of the DA/reward hypothesis regularly cite motivational theorists and employ their language. Nevertheless, considerable evidence indicates that low/moderate doses of DA antagonists, and depletions of DA in nucleus accumbens, can suppress instrumental responding for food while, at the same time, these conditions leave fundamental aspects of reinforcement (i.e. primary or unconditioned reinforcement; primary motivation or primary incentive properties of natural reinforcers) intact. Several complex features of the literature on dopaminergic involvement in reinforcement are examined below, and it is argued that the assertions that DA mediates 'reward' or 'reinforcement' are inaccurate and grossly oversimplified. Thus, it appears as though it is no longer tenable to assert that drugs of abuse are simply turning on the brain's natural 'reward system'. In relation to the hypothesis that DA systems are involved in 'wanting', but not 'liking', it is suggested in the present review that 'wanting' has both directional aspects (e.g. appetite to consume food) and activational aspects (e.g. activation for initiating and sustaining instrumental actions; tendency to work for food). The present paper reviews findings in support of the hypothesis that low doses of DA antagonists and accumbens DA depletions do not impair appetite to consume food, but do impair activational aspects of motivation. This suggestion is consistent with the studies showing that low doses of DA antagonists and accumbens DA depletions alter the relative allocation of instrumental responses, making the animals less likely to engage in instrumental responses that have a high degree of work-related response costs. In addition, this observation is consistent with studies demonstrating that accumbens DA depletions make rats highly sensitive to ratio requirements on operant schedules. Although accumbens DA is not seen as directly mediating appetite to consume food, principles of behavioral economics indicate that accumbens DA could be involved in the elasticity of demand for food in terms of the tendency to pay work-related response costs. Future research must focus upon how specific aspects of task requirements (i.e. ratio requirements, intermittence of reinforcement, temporal features of response requirements, dependence upon conditioned stimuli) interact with the effects of accumbens DA depletions, and which particular factors determine sensitivity to the effects of DA antagonism or depletion.

Neural activities in the substantia nigra modulated by stimulation of the orofacial motor cortex and rhythmical jaw movements in the rat

Neurons related to jaw movements in the substantia nigra pars reticulata were explored by examining changes in their neural activities in response to electrical stimulation of the orofacial sensorimotor cortex and during rhythmical jaw movements induced by mechanical stimulation applied to the oral cavity in the rat. Out of 80 neurons tested, 59 showed changes in their firing patterns of activities in response to the electrical stimulation of the cortex. The responding neurons were mainly located in the dorsolateral part of the substantia nigra pars reticulata. The substantia nigra pars reticulata neurons showing responses were classified into the following five types according to their response patterns: (1) an inhibition preceded by an early excitation and followed by a late excitation (n = 26), (2) an inhibition preceded by an early excitation but not followed by a late excitation (n = 7), (3) an inhibition not preceded by an early excitation but followed by a late excitation (n = 2), (4) an inhibition without early or late excitations (n = 7) and (5) an excitation without an inhibition (n = 17). Out of 18 neurons responding to the cortical stimulation, 11 (61.1%) increased or decreased their neural activities during rhythmical jaw movements. Some of these neurons had a projection to the lateral part of the superior colliculus (n = 5) and/or to the parvicellular reticular formation (n = 2). These results provide first neurophysiological evidence for neurons in the dorsolateral part of the substantia nigra pars reticulata with inputs from and outputs to the areas related to jaw movements. These neurons may participate in the control of jaw movements in the rat.

Learning and memory functions of the Basal Ganglia

Although the mammalian basal ganglia have long been implicated in motor behavior, it is generally recognized that the behavioral functions of this subcortical group of structures are not exclusively motoric in nature. Extensive evidence now indicates a role for the basal ganglia, in particular the dorsal striatum, in learning and memory. One prominent hypothesis is that this brain region mediates a form of learning in which stimulus-response (S-R) associations or habits are incrementally acquired. Support for this hypothesis is provided by numerous neurobehavioral studies in different mammalian species, including rats, monkeys, and humans. In rats and monkeys, localized brain lesion and pharmacological approaches have been used to examine the role of the basal ganglia in S-R learning. In humans, study of patients with neurodegenerative diseases that compromise the basal ganglia, as well as research using brain neuroimaging techniques, also provide evidence of a role for the basal ganglia in habit learning. Several of these studies have dissociated the role of the basal ganglia in S-R learning from those of a cognitive or declarative medial temporal lobe memory system that includes the hippocampus as a primary component. Evidence suggests that during learning, basal ganglia and medial temporal lobe memory systems are activated simultaneously and that in some learning situations competitive interference exists between these two systems.

Dopamine depletion causes fragmented clustering of neurons in the sensorimotor striatum: evidence of lasting reorganization of corticostriatal input

Firing during sensorimotor exam was used to categorize single neurons in the lateral striatum of awake, unrestrained rats. Five rats received unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle to deplete striatal dopamine (DA; >98% depletion, postmortem assay). Three months after treatment, rats exhibited exaggerated rotational behavior induced by L-dihydroxyphenylalanine (L-DOPA) and contralateral sensory neglect. Electrode track "depth profiles" on the DA-depleted side showed fragmented clustering of neurons related to sensorimotor activity of single body parts (SBP neurons). Clusters were smaller than normal, and more SBP neurons were observed in isolation, outside of clusters. More body parts were represented per unit volume. No recovery in these measures was observed up to one year post lesion. Overall distributions of neurons related to different body parts were not altered. The fragmentation of SBP clusters after DA depletion indicates that a percentage of striatal SBP neurons switched responsiveness from one body part to one or more different body parts. Because the specific firing that characterizes striatal SBP neurons is mediated by corticostriatal inputs (Liles and Updyke [1985] Brain Res. 339:245-255), the data indicate that DA depletion resulted in a reorganization of corticostriatal connections, perhaps via unmasking or sprouting of connections to adjacent clusters of striatal neurons. After reorganization, sensory activity in a localized body part activates striatal neurons that have switched to that body part. In turn, switched signals sent from basal ganglia to premotor and motor neurons, which likely retain their original connections, would create mismatches in these normally precise topographic connections. Switched signals could partially explain parkinsonian deficits in motor functions involving somatosensory guidance and their intractability to L-DOPA therapy-particularly if the switching involves sprouting.

Feeding-induced decrease in extracellular glutamate level in the rat nucleus accumbens: dependence on glutamate uptake

In vivo microdialysis combined with high-performance liquid chromatography and electrochemical detection was used to monitor extracellular glutamate levels in the medial nucleus accumbens of Sprague-Dawley rats during their feeding behaviour. Consumption of a palatable new diet or a diet to which rats were previously exposed caused a decrease in extracellular level of glutamate in the nucleus accumbens during and after feeding. The presentation of an inedible object (a piece of rubber) instead of the expected food caused a marked increase in extracellular glutamate levels. In contrast, if the piece of rubber was presented to rats that did not expect food delivery, the extracellular level of glutamate remained unchanged during the rubber presentation. The feeding-induced decrease in the extracellular glutamate level did not depend on food deprivation and was completely prevented by intraaccumbal infusions through the dialysis probe of 10 mM D,L-threo-beta-hydroxyaspartate (a glutamate uptake inhibitor). Intraaccumbal infusions of 10 microM S-(-)-raclopride L-tartrate (a D2/D3 dopamine receptor antagonist) or 1 microM tetrodotoxin (a voltage-dependent Na(+) channel blocker) also completely reversed the decrease in extracellular glutamate level in response to food intake. The D1/D5 dopamine receptor antagonist SCH-23390 (10 microM) administered into the nucleus accumbens had no significant effect on the feeding-induced decrease in extracellular glutamate level. From the data obtained we suggest that the decrease in the extracellular level of glutamate in the medial nucleus accumbens in response to feeding appears to arise from a temporal increase in glutamate uptake that is probably operated by dopamine inputs to the nucleus accumbens via D2/D3 receptors. Our findings also suggest that the dissociation between the expected biological value of a presented object and the reality might be an important determinant for regulation of glutamate release in this brain area during feeding behaviour.

Role of the dorsomedial striatum in behavioral flexibility for response and visual cue discrimination learning

These experiments examined the effects of dorsomedial striatal inactivation 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. 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. Infusions of 2% tetracaine did not impair acquisition of the response or visual cue discrimination but impaired performance when shifting from a response to a visual cue discrimination, and vice versa. Analysis of the errors revealed that the deficit was not due to perseveration of the previously learned strategy, but to an inability to maintain the new strategy. These results contrast with findings indicating that prelimbic inactivation impairs behavioral flexibility due to perseveration of a previously learned strategy. Thus, specific circuits in the prefrontal cortex and striatum may interact to enable behavioral flexibility, but each region may contribute to distinct processes that facilitate strategy switching.

Disruption of the two-state membrane potential of striatal neurones during cortical desynchronisation in anaesthetised rats

In anaesthetised animals, the very negative resting membrane potential of striatal spiny neurones (down state) is interrupted periodically by depolarising plateaux (up states) which are probably driven by excitatory input. In the absence of active synaptic input, as occurs in vitro, potassium currents hold the membrane potential of striatal spiny neurones in the down state. Because striatal spiny neurones fire action potentials only during the up state, these plateau depolarisations have been perceived as enabling events that allow information processing through cerebral cortex-basal ganglia circuits. Recent studies have demonstrated that the robust membrane potential fluctuation of spiny neurones is strongly correlated to the slow electroencephalographic rhythms that are typical of slow wave sleep and anaesthesia. To further understand the impact of cortical activity states on striatal function, we studied the membrane potential of striatal neurones during cortical desynchronised states. Simultaneous in vivo recordings of striatal neurones and the electrocorticogram in urethane-anaesthetised rats revealed that rhythmic alternation between up and down states was disrupted during episodes of spontaneous or induced cortical desynchronisation. Instead of showing robust two-state fluctuations, the membrane potential of striatal neurones displayed a persisting depolarised state with fast, low-amplitude modulations. Spiny neurones remained in this persistent up state until the cortex resumed ~1 Hz synchronous activity. Most of the recorded neurones exhibited a low firing probability, irrespective of the cortical activity state. Time series analysis failed to reveal significant correlations between the membrane potential of striatal neurones and the desynchronised electrocorticogram. Our results suggest that during cortical desynchronisation continuous uncorrelated excitatory input sustains the membrane potential of striatal neurones in a persisting depolarised state, but that substantial additional input is necessary to impel the neurones to threshold. Our data support that the prevailing cortical activity state determines the duration of the enabling depolarising events that take place in striatal spiny neurones.

Lead exposure and dorsomedial striatum mediation of fixed interval schedule-controlled behavior

Prior studies demonstrate a critical role for mesolimbic dopamine systems, particularly nucleus accumbens, in the mediation of fixed interval (FI) schedule-controlled behavior and an enhancement of nucleus accumbens dopamine activity as a mechanism of chronic postweaning lead (Pb)-induced increases in Fl response rates. Since dorsomedial striatum, like nucleus accumbens, receives limbic input, it could also conceivably contribute to Pb-related effects on FI performance. Therefore, changes in FI schedule-controlled behavior were examined following administration of dopamine or the non-specific irreversible dopamine antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) into dorsomedial striatum of rats exposed from weaning to 0, 50 or 500 ppm Pb acetate drinking solutions. The 500 ppm exposure increased baseline FI response rates relative to both 0 and 50 ppm. Intra-dorsomedial striatum EEDQ and dopamine had no effects when examined across all animals. However, both compounds produced rate-dependent effects, i.e. increases or decreases in rate in different subjects, depending upon baseline Fl overall rates. The rate-increasing effects of intra-dorsomedial striatum dopamine actually mimicked Pb effects, increasing Fl overall and run rates and shortening postreinforcement pause times. Further, Pb exposure modulated effects of dopamine and EEDQ in dorsomedial striatum. While these collective findings conceivably suggest dorsomedial striatum as another potential site through which postweaning Pb exposure influences FI performance, this possibility is not supported by other studies that show that chronic postweaning Pb alters dopamine binding sites and evoked dopamine release in nucleus accumbens but not in dorsomedial striatum even over a year exposure period. Thus, while both regions may play a role in mediating Fl performance under normal conditions, it appears that alterations in nucleus accumbens dopamine activity may be sufficient to induce chronic postweaning Pb-induced increases in FI response rates.

Effects of intralaminar thalamic nuclei lesion on glutamic acid decarboxylase (GAD65 and GAD67) and cytochrome oxidase subunit I mRNA expression in the basal ganglia of the rat

This study investigated the influence of thalamic inputs on neuronal metabolic activity in the rat basal ganglia. By means of in situ hybridization histochemistry, we examined the consequences of ibotenate-induced unilateral lesion of intralaminar thalamic nuclei on mRNA expression of cytochrome oxidase subunit-I (CoI) in the striatum and the subthalamic nucleus (STN) and of the two isoforms of glutamate decarboxylase (GAD65 and GAD67) in the striatum, globus pallidus (GP), entopeduncular nucleus (EP) and substantia nigra pars reticulata (SNr). In the striatum, GAD67 mRNA expression decreased selectively in the rostral part of the structure at 5 and 12 days postlesion (approximately -30%), whereas, GAD65 mRNA levels was downregulated only in the caudal striatum at 12 days (-29%). In both the striatum and STN, CoI mRNA expression decreased ipsilaterally at 5 and bilaterally at 12 days. In GP, GAD67 and GAD65 mRNA expression decreased ipsilaterally at 5 (-20% and -26%) and 12 days (-23% and -36%). In EP, selective bilateral decreases in GAD67 mRNA expression were found at 5 and 12 days (-50% and -40%). Conversely, in SNr, only GAD65 mRNA expression was reduced bilaterally at both time points. These data show that the thalamus exerts a widespread excitatory influence on the basal ganglia network that cannot be accounted for solely by its known direct connections. Given the recent data showing that intralaminar thalamic nuclei are a major nondopaminergic site of neurodegeneration in Parkinson's disease, these results may have a critical bearing on understanding the cellular basis of basal ganglia dysfunction in parkinsonism.

Modeling Parkinson's disease in rats: an evaluation of 6-OHDA lesions of the nigrostriatal pathway

Human idiopathic Parkinson's disease (PD) is a progressive neurodegenerative disorder that is primarily characterized by degeneration of the dopaminergic neurons of the nigrostriatal pathway. Different 6-OHDA rat models of PD have been developed in which this toxin has been injected into different parts of the nigrostriatal pathway: (a) the medial forebrain bundle which leads to extensive dopamine (DA) depletion; (b) the substantia nigra pars compacta, which leads to more specific and moderate DA depletions; and (c) subregions of the caudate-putamen complex (CPu), which also leads to specific DA depletions. In this article we review the dopaminergic depletion and behavioral consequences of 6-OHDA lesions in the rat. It was examined whether the relation between DA depletion and behavioral deficits mimic idiopathic PD. In addition, it was evaluated which model most closely approximates the human situation, especially in relation to the stage of this progressive disease. It was concluded that with respect to the site of the lesion, rats with partial lesions of the ventrolateral CPu are the most appropriate models to study early and late stages of PD. The choice of the behavioral parameters determines the use of unilateral or bilateral lesions, although it is obvious that the bilateral model mimics the human situation more closely.

Dopamine-dependent plasticity of corticostriatal synapses

Knowledge of the effect of dopamine on corticostriatal synaptic plasticity has advanced rapidly over the last 5 years. We consider this new knowledge in relation to three factors proposed earlier to describe the rules for synaptic plasticity in the corticostriatal pathway. These factors are a phasic increase in dopamine release, presynaptic activity and postsynaptic depolarisation. A function is proposed which relates the amount of dopamine release in the striatum to the modulation of corticostriatal synaptic efficacy. It is argued that this function, and the experimental data from which it arises, are compatible with existing models which associate the reward-related firing of dopamine neurons with changes in corticostriatal synaptic efficacy.

A single exposure to restraint stress induces behavioral and neurochemical sensitization to stimulating effects of amphetamine: involvement of NMDA receptors

Evidence indicates that repeated exposure to stressful events sensitizes the motor and addictive effects of drugs of abuse in rats. Regarding a single exposure to one restraint stress, previous findings have shown that it is sufficient to induce behavioral sensitization to stimulating and reinforcing properties of abuse drugs (e.g., amphetamine and morphine), as measured by locomotor activity and conditioned place preference, respectively. It is well known that enhanced dopaminergic neurotransmission in the nucleus accumbens and striatum plays a critical role in the development and/or expression of repeated stress-induced or drug-induced sensitization. In addition, involvement of NMDA receptors has been implicated in its development. However, whether sensitization induced by a single restraint stress exposure represents the same neurobiologic phenomenon is unknown. We studied the following issues: (a) influence of a single restraint exposure on the stimulating effects of amphetamine on dopamine release by microdialysis from striatum and (b) involvement of glutamatergic pathways, specifically those innervating striatum, on stress-induced sensitization to amphetamine, by administering MK-801 ip (0.1 mg/kg) or intrastriatally (1 microg/0.5 microL) previous to an acute restraint stress. For microdialysis studies (a) or intrastriatal administration of MK-801 (b), Wistar rats (250-330 g) were implanted stereotactically under anesthesia with a guide cannula in the striatum. After 2 days, animals were immobilized for 2 hours in a Plexiglas device. Control animals remained in their home cages. The following day we evaluated the stimulating effect of amphetamine on (a) dopamine release from striatum or (b) locomotor activity. In studies (a), dialysis probes were inserted into the guide cannula, and baseline dopamine levels were collected for 2 hours before a challenge of amphetamine (1.5 mg/kg i.p.). Dialysates were then collected by 3 hours. Amphetamine challenge induced a significantly higher increase in dopamine release and locomotor activity in animals previously subjected to one restraint stress exposure, relative to that observed in the no-restraint stress group. MK-801 administered i.p. or intrastriatally blocked the restraint stress-induced sensitization to amphetamine. First, our results point out that a single restraint stress exposure is a pertinent stimulus to induce sensitization of amphetamine's stimulating effects on dopaminergic neurotransmission in the striatum. Secondly, NMDA-glutamatergic receptors, specifically those placed in the striatum, are implicated in the development of stress restraint-induced sensitization.

Emotion and motivation: the role of the amygdala, ventral striatum, and prefrontal cortex

Emotions are multifaceted, but a key aspect of emotion involves the assessment of the value of environmental stimuli. This article reviews the many psychological representations, including representations of stimulus value, which are formed in the brain during Pavlovian and instrumental conditioning tasks. These representations may be related directly to the functions of cortical and subcortical neural structures. The basolateral amygdala (BLA) appears to be required for a Pavlovian conditioned stimulus (CS) to gain access to the current value of the specific unconditioned stimulus (US) that it predicts, while the central nucleus of the amygdala acts as a controller of brainstem arousal and response systems, and subserves some forms of stimulus-response Pavlovian conditioning. The nucleus accumbens, which appears not to be required for knowledge of the contingency between instrumental actions and their outcomes, nevertheless influences instrumental behaviour strongly by allowing Pavlovian CSs to affect the level of instrumental responding (Pavlovian-instrumental transfer), and is required for the normal ability of animals to choose rewards that are delayed. The prelimbic cortex is required for the detection of instrumental action-outcome contingencies, while insular cortex may allow rats to retrieve the values of specific foods via their sensory properties. The orbitofrontal cortex, like the BLA, may represent aspects of reinforcer value that govern instrumental choice behaviour. Finally, the anterior cingulate cortex, implicated in human disorders of emotion and attention, may have multiple roles in responding to the emotional significance of stimuli and to errors in performance, preventing responding to inappropriate stimuli.

Nicotine alters striatal glutamate function and decreases the apomorphine-induced contralateral rotations in 6-OHDA-lesioned rats

The overall goal of this study was to determine the effects of subchronic nicotine (0.4 mg/kg) treatment for 7 or 14 days on striatal glutamate function in both naïve and in 6-hydroxydopamine (6-OHDA)-treated rats in which the nigrostriatal dopamine pathway was lesioned. In lesioned animals, the effect of nicotine on apomorphine-induced contralateral rotations was also assessed. In naïve rats, once daily nicotine administration for 7 or 14 days resulted in a decrease and then an increase, respectively, in the basal extracellular level of striatal glutamate compared to the saline-treated group. Ultrastructurally, 14-day treatment with nicotine resulted in an increase in the density of striatal glutamate immunolabeling within nerve terminals making an asymmetrical synaptic contact compared to the saline-treated group. In 6-OHDA-lesioned animals, coadministration of nicotine with apomorphine or nicotine alone for 7 days resulted in an increase in the density of nerve terminal glutamate immunolabeling, compared to the apomorphine- or saline-treated groups. However, coadministration of nicotine with apomorphine for 14 days resulted in a decrease in the density of nerve terminal glutamate immunolabeling compared to the nicotine-treated group. Following subchronic treatment of 6-OHDA-lesioned rats with apomorphine for 7 or 14 days, there was an increase in the number of apomorphine-induced contralateral rotations compared to the saline treated group. There was a decrease in the number of apomorphine-induced contralateral rotations in the group coadministered nicotine with apomorphine for 7 or 14 days compared to the apomorphine treated group. The data suggests that in this 6-OHDA lesion model of Parkinson's disease, treatment with nicotine may be useful in counteracting the increased behavioral effect (i.e., contralateral rotations) observed after treatment with a dopamine agonist, such as apomorphine.

A rostro-caudal dissociation in the dorsal and ventral striatum of the juvenile SHR suggests an anterior hypo- and a posterior hyperfunctioning mesocorticolimbic system

Functional molecular neuroimaging techniques have been applied to the study of the neural substrates of Attention-Deficit Hyperactivity Disorder (ADHD) in an animal model, the juvenile SHR rat. They include quantitative receptor autoradiography and immunocytochemistry for neuronal markers such as Ca2+/Calmodulin Dependent Kinase II (CaMKII) and transcription factors. Multiple evidence emerges for a rostro caudal dissociation within the dorsal (DS) and ventral striatum (VS) (n. accumbens) and olfactory tubercle (OT). It consists in (i) a higher density of dopamine (DA) D-1/D-5 receptor binding sites in a discrete segment of the anterior forebrain that comprises the DS, VS and OT, (ii) a lower density of DA D-2/D-3 autoreceptors in the caudal portion of the n. accumbens shell subterritory, (iii) a reduced number of CaMKII and c-FOS positive elements only in the anterior portion of DS and VS (iv) reversal by repeated injections of methylphenidate (MP) (3 mg/kg, 14 days) with 'downregulation' in SHR and 'up-regulation' in the WKY control rats of DS and VS of DA D-1/D-5 receptors. Thus, under basal conditions the mesocorticolimbic (MCL) DA system appears to be hyperfunctioning rather than hypofunctioning, as demonstrated (i) by subsensitivity of presynaptic D-3 autoreceptors and (ii) by phasic inhibition of MCL activity induced by acute blockade of endocannabinoid reuptake using AM404. Following MP treatment, the hyperfunctioning MCL DA system turns into a hypofunctioning one, as earlier suggested by Solanto. Since the target neurons of MCL fibers seem to be uncoupled to D-1 receptors, the medium spiny GABA neurons projecting to the ventral pallidum and ventral tegmental area (VTA) exert a weak feedback inhibition on the neurons of origin of MCL system. Therefore, MCL neurons maintain a high basal activity with consequences on the cortico-striato-pallido-thalamo-cortical system and amygdala complex through the 'extended amygdala system'. While the former explains the attention, motivation and activity alterations of this rat model of ADHD, the latter explains the emotional symptoms of the syndrome. It remains to be ascertained the starting point in the network leading eventually to the segmental defect as well as its significance in humans.

Position sensitivity in phasically discharging nucleus accumbens neurons of rats alternating between tasks requiring complementary types of spatial cues

To determine how hippocampal location-selective discharges might influence downstream structures for navigation, nucleus accumbens neurons were recorded in rats alternating between two tasks guided respectively by lit cues in the maze or by extramaze room cues. Of 144 phasically active neurons, 80 showed significant behavioral correlates including displacements, immobility prior to, or after reward delivery, as well as turning, similar to previous reports. Nine neurons were position-selective, 22 were sensitive to task and platform changes and 40 others were both. Although the accumbens neurons showed the same behavioral correlate in two or four functionally equivalent locations, these responses were stronger at some of these places, evidence for position sensitivity. To test whether position responses were selective for room versus platform cues, the experimental platform was rotated while the rat performed each of the two tasks. This revealed responses to changes in position relative to both platform and room cues, despite the fact that previous studies had shown that place responses of hippocampal neurons recorded in the same task are anchored to room cues only. After these manipulations and shifts between the two tasks, the responses varied among simultaneously recorded neurons, and even in single neurons in alternating visits to reward sites. Again this contrasts with the uniformity of place responses of hippocampal neurons recorded in this same task. Thus accumbens position responses may derive from hippocampal inputs, while responses to context changes are more likely to derive from other signals or intrinsic processing. Considering the accumbens as a limbic-motor interface, we conclude that position-modulated behavioral responses in the accumbens may be intermediate between the allocentric reference frame of position-selective discharges in the hippocampus and the egocentric coding required to organize movement control. The conflicting responses among simultaneously recorded neurons could reflect competition processes serving as substrates for action selection and learning.

Multiple parallel memory systems in the brain of the rat

A theory of multiple parallel memory systems in the brain of the rat is described. Each system consists of a series of interconnected neural structures. The "central structures" of the three systems described are the hippocampus, the matrix compartment of the dorsal striatum (caudate-putamen), and the amygdala. Information, coded as neural signals, flows independently through each system. All systems have access to the same information from situations in which learning occurs, but each system is specialized to represent a different kind of relationship among the elements (stimulus events, responses, reinforcers) of the information that flows through it. The speed and accuracy with which a system forms a coherent representation of a learning situation depend on the correspondence between the specialization of the system and the relationship among the elements of the situation. The coherence of these stored representations determines the degree of control exerted by each system on behavior in the situation. Although they process information independently the systems interact in at least two ways: by simultaneous parallel influence on behavioral output and by directly influencing each other. These interactions can be cooperative (leading to similar behaviors) or competitive (leading to different behaviors). Experimental findings consistent with these ideas, mostly from experiments with rats, are reviewed.

Activation of cAMP-dependent protein kinase suppresses the presynaptic cannabinoid inhibition of glutamatergic transmission at corticostriatal synapses

In a previous study, we showed that type 1 cannabinoid (CB(1)) receptor activation substantially depresses the corticostriatal glutamatergic transmission onto striatal neurons in the brain slice preparation. We now report that the adenylyl cyclase activator forskolin and cAMP analog (S)-p-8-(4-chlorophenythil) adenosine-3',5'-monophosphorothioate (Sp-8-CPT-cAMPS) strongly suppressed the synaptic depression induced by cannabimimetic aminoalkylindole, WIN 55,212-2. Application of the cAMP-dependent protein kinase (PKA) inhibitor KT5720 alone had no consistent effect on basal synaptic transmission but the synaptic enhancement elicited by forskolin was blocked. In addition, pretreatment of striatal slices with either KT5720 or another PKA inhibitor, H89, completely abolished the attenuation by forskolin on WIN 55,212-2-induced synaptic depression. The effect of forskolin on CB(1) receptor function was still observed in a low Ca(2+) bathing solution, suggesting that the forskolin's action is not attributable to its ability to saturate the presynaptic transmitter release processes. The possibility that forskolin acted by increasing CB(1) receptor phosphorylation was confirmed by demonstrating that the serine-phosphorylated component with CB(1) receptors was significantly increased after forskolin treatment. This forskolin effect was markedly attenuated in the presence of KT5720. Moreover, the activation of beta-adrenergic receptors by isoproterenol mimics forskolin to elicit a PKA-dependent inhibition of CB(1) receptor function. Together, these observations indicate that the presynaptic inhibitory action of CB(1) receptors at corticostriatal synapses could be negatively regulated by cAMP/PKA-mediated receptor phosphorylation. This effect of PKA may play a functional role in fine-tuning glutamatergic transmission at corticostriatal synapses.

Role of the dorsomedial striatum in behavioral flexibility for response and visual cue discrimination learning

These experiments examined the effects of dorsomedial striatal inactivation 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. 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. Infusions of 2% tetracaine did not impair acquisition of the response or visual cue discrimination but impaired performance when shifting from a response to a visual cue discrimination, and vice versa. Analysis of the errors revealed that the deficit was not due to perseveration of the previously learned strategy, but to an inability to maintain the new strategy. These results contrast with findings indicating that prelimbic inactivation impairs behavioral flexibility due to perseveration of a previously learned strategy. Thus, specific circuits in the prefrontal cortex and striatum may interact to enable behavioral flexibility, but each region may contribute to distinct processes that facilitate strategy switching.

Principles of rat subcortical forebrain organization: a study using histological techniques and multiple fluorescence labeling

In the present study, we introduce new views on neuro- and chemoarchitectonics of the rat forebrain subcortex deduced from traditional and current concepts of anatomical organization and from our own results. It is based on double and triple immunofluorescence of markers for transmitter-related enzymes, calcium-binding proteins, receptor proteins, myelin basic protein (MBP) and neuropeptides, and on histological cell/myelin stains. The main findings can be summarized as follows: (i) the dorsal striatum of rat and other myomorph rodents reveals a small caudate equivalent homotopic to the caudate nucleus (C) of other mammals, and a large putamen (Pu). (ii) Shell and core can be distinguished also in the 'rostral pole' of nucleus accumbens (ACC) with the calretinin/calbindin and neuropeptide Y (NPY) immunostaining. The shell reveals characteristics of a genuine striatal but not of an extended amygdala (EA) subunit. (iii) EA and lateral septum show striking similarities in structure and fiber connections and may therefore represent a separate parastriatal complex. (iv) The meandering dense layer (DL) of olfactory tubercle (OT) forms longitudinal gyrus- and sulcus-like structures converging in its rostral pole. (v) The core regions of the islands of Calleja that border the ventral pallidum (VP) sharing some of its features are invaded by myelinated fibers of the medial forebrain bundle (MFB). The island of Calleja magna is also apposed to an inconspicuous, slender dorsal appendage of VP. (vi) The VP is composed of a large dorsal reticulated part traversed by the myelinated GABAergic parvalbumin-immunoreactive axons of the MFB and a slender ventral non-reticulate part close to the islands of Calleja. (vii) Considering their close association to the limbic system, ventral striatum (VS) and VP may represent the oldest part of basal ganglia, whereas dorsal striatopallidal subunits were progressively developed in parallel to the growing neocortical influence on motor behavior.

Site-specific actions of interleukin-1 on excitotoxic cell death in the rat striatum

The pro-inflammatory cytokine interleukin-1 (IL-1) contributes to and exacerbates many forms of neurodegeneration. When co-administered with the potent glutamatergic agonist S-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (S-AMPA) in the rat striatum, IL-1 induces marked and widespread cell death throughout the ipsilateral cortex. The mechanisms underlying this action of IL-1 are not known but may involve activation of polysynaptic neuronal pathways leading from the striatum to the cortex via other brain areas such as the hypothalamus. The aims of the present study were to identify specific sites of action of IL-1 in the rat striatum, in order to further understand these pathways. Ventral regions of the caudate-putamen and the lateral shell of the nucleus accumbens (NAcc) were particularly sensitive to the effects of IL-1 on excitotoxic damage. A high percentage of co-injections in these sites induced distant cortical damage, whereas injections in more dorsal areas of the caudate-putamen or core regions of the NAcc were less likely to result in cortical cell death. The 'positive' injection sites differ from the unresponsive areas in that they have extensive connections with the limbic system and it may be that IL-1 displays specific actions on limbic pathways that, in conjunction with AMPA/kainate receptor activation, contribute to the remote cell death in the cortex. These findings enhance our understanding of the actions of IL-1, and the mechanisms by which it participates in neurodegeneration through both local and long-range effects.

Dopamine D2 receptors are present in prefrontal cortical afferents and their targets in patches of the rat caudate-putamen nucleus

Glutamatergic neurons within the deep layers of the prefrontal cortex and dopaminergic neurons of the substantia nigra pars compacta preferentially terminate in patch-like regions within the caudate putamen nucleus (CPN). Activation of dopamine D2 receptors is known to potently modulate striatal glutamatergic transmission and may play a role in reward-based motor learning. To determine the cellular substrate for D2-mediated regulation of prefrontal corticostriatal transmission in striatal patches, we combined anterograde transport of biotinylated dextran amine (BDA) with immunogold-silver labeling of a D2 receptor antipeptide antiserum in rat brain. Injections centered in deep layers of the dorsal part of the anterior cingulate cortex, one of the prefrontal cortical regions, produced varicose axonal BDA labeling in a patch-like distribution in the dorsomedial CPN. Electron microscopy showed that in these patch compartments, BDA labeling was present exclusively in axons and terminals (total number = 581), 9% of which contained detectable D2-like immunoreactivity. Thirty percent of the BDA-labeled terminals formed asymmetric excitatory synapses with dendritic spine heads, and the remainder were without recognizable junctions. The recipient spines were unlabeled or contained immunogold-silver particles for D2 receptors. A few of the D2-labeled spines also received convergent, often nonsynaptic contact from D2-labeled terminals resembling dopaminergic afferents. In addition, the corticostriatal terminals often apposed spiny and nonspiny neuronal profiles that contained D2 labeling. These results suggest that dopamine D2 receptors are strategically positioned for presynaptic and postsynaptic modulation of prefrontal corticostriatal excitation of spiny neurons in striatal patches. The findings have direct implications for D2-mediated control of reward-related motor learning.

Activation of metabotropic glutamate receptor mediates upregulation of transcription factor mRNA expression in rat striatum induced by acute administration of amphetamine

Metabotropic glutamate receptors (mGluRs) are densely expressed on the medium spiny projection neurons of rat striatum. Intrastriatal injection of an mGluR agonist increases motor activity and dopamine release in the striatum. This study investigated the roles of mGluRs in the regulation of behavioral activity and transcription factor gene expression in striatal neurons in normal and amphetamine-treated rats. Acute injection of a behaviorally active dose of amphetamine (4.0 mg/kg, i.p.) elevated basal levels of the transcription factor c-fos and zif/268 mRNAs in the dorsal striatum as revealed by quantitative in situ hybridization. Pharmacological blockade of mGluRs with bilateral injections of a non-selective mGluR antagonist, (S)-alpha-methyl-4-carboxyphenylglycine (MCPG), into the dorsal striatum at 10 but not 0.4 nmol significantly attenuated amphetamine-stimulated c-fos mRNA expression in this area. In contrast to c-fos, striatal zif/268 induction stimulated by amphetamine was not altered by pretreatment with MCPG. MCPG by itself did not affect basal levels of either gene expression in the striatum. No significant effects of MCPG were found on spontaneous or amphetamine-stimulated behavioral activities. These data indicate that blockade of total mGluRs in the dorsal striatum has a selective effect on dopamine-stimulated gene expression. Activation of the MCPG-sensitive mGluRs is required for the upregulation of transcription factor c-fos, although not zif/268, mRNA expression in the striatum in response to acute injection of amphetamine.

Atropine reduces raclopride-induced muscle rigidity by acting in the ventral region of the striatum

Parkinson-like extrapyramidal motor side effects associated with the use of antipsychotic drugs, such as increased muscle rigidity, are thought to result from blockade of striatal dopamine D2 receptors. While anticholinergic medications (muscarinic receptor antagonists) ameliorate extrapyramidal side effects, the mechanisms underlying their effectiveness remain unclear. We investigated the site of action of atropine, a non-selective muscarinic receptor antagonist, in reducing increased muscle rigidity, assessed as increases in tonic electromyographic (EMG) activity, induced by the selective dopamine D2 receptor antagonist, raclopride. Atropine significantly reduced raclopride-induced EMG increases in rat hindlimb muscles, when injected into the ventral striatum, but not the dorsal striatum or the substantia nigra. Atropine's site of action was localised to a small area of muscarinic receptors within the ventral part of the striatum, using quantitative autoradiography. These findings provide new information about the regulation of motor control by muscarinic receptor antagonists and additional evidence about the functional heterogeneity of the striatum.

The role of the globus pallidus D2 subfamily of dopamine receptors in pallidal immediate early gene expression

The globus pallidus plays an important role in basal ganglia circuitry, representing the first relay nucleus of the 'indirect pathway' of striatal efferents. In contrast to the well-characterized actions of dopamine on striatal neurons, the functional role of the dopamine innervation of globus pallidus is less well understood. Previous research showed that systemic administration of either a dopamine D2 receptor antagonist or combined dopamine D1 and D2 receptor agonists induces Fos, the protein product of the immediate early gene c-fos, in neurons of globus pallidus [Ruskin and Marshall (1997) Neuroscience 81, 79-92]. To determine whether the ability of the D2 receptor antagonist, sulpiride, to induce Fos in rat pallidal neurons is mediated by D2-like receptors in striatum or globus pallidus, intrastriatal or intrapallidal sulpiride infusions were conducted. The diffusion of intrastriatal sulpiride was estimated by measuring this antagonist's competition for N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ)-induced D2 receptor inactivation. The phenotype of the striatal neurons expressing Fos after intrastriatal infusion was assessed by combining Fos immunocytochemistry with D2 receptor mRNA in situ hybridization. Intrastriatal infusions of (-)-sulpiride (10-200 ng) dose-dependently increased the number of striatal cells expressing Fos; and the Fos-immunoreactive striatal cells were D2 receptor mRNA-expressing, the same population in which systemic D2 receptor antagonists induce Fos. Intrastriatal infusions of high (5 microg), but not low (10-200 ng), (-)-sulpiride doses also induced Fos in globus pallidus cells but the sulpiride appeared to spread to the globus pallidus. Direct intrapallidal infusions of (-)-sulpiride (50-100 ng) dose-dependently induced Fos in globus pallidus with minimal influence on striatum or other basal ganglia structures. Using sensitive in situ hybridization conditions, prominent labeling of D2 receptor mRNA was evident in globus pallidus. D2 receptor mRNA was densest in a lateral 200 microm wide band that follows the curvature of the pallidal/striatal boundary. Cellular analysis revealed silver clusters associated with D2 receptor mRNA labeling over globus pallidus neurons that were immunoreactive for neuron-specific nuclear protein. These results strongly suggest that the dopaminergic innervation of globus pallidus, acting through D2-like receptors internal to this structure, can control gene expression in pallidal neurons.

Regional differences in the expression of corticostriatal synaptic plasticity

Field recordings of responses to activation of corticostriatal afferents were made in coronally sectioned rat brain slices. Each recording site was categorized according to its medial to lateral and rostral to caudal position to investigate anatomical differences in synaptic plasticity. Individual responses were highly variable exhibiting extremes of tetanus induced depression and potentiation. Consequently, averaging masked the capacity of these synapses to express long-term forms of plasticity. Block of GABA(A) inhibition and elimination of dopaminergic input with 6-hydroxydopamine lesions both acted to increase the expression of potentiation, but again considerable variability was observed. Separation of recordings into medial and lateral groups revealed clear anatomical trends which contributed to the variability observed in the total sample. Paired-pulse, post-tetanic and long-term potentiation was greater in medial than in lateral groups in normal artificial cerebral spinal fluid. Similar tendencies were seen after block of GABA(A) receptors with bicuculline. 6-Hydroxydopamine lesions in combination with bicuculline treatment reduced medial to lateral differences. Factoring in medial to lateral trends revealed block of GABA(A) receptor mediated inhibition had its greatest effect on medial corticostriatal responses and 6-hydroxydopamine lesions had their greatest effect on lateral responses. From these data we suggest anatomical variation in striatal circuitry may underlie regional differences in synaptic plasticity evoked by corticostriatal activation.

Augmented motor activity and reduced striatal preprodynorphin mRNA induction in response to acute amphetamine administration in metabotropic glutamate receptor 1 knockout mice

Metabotropic glutamate receptor 1 (mGluR1) is a G-protein-coupled receptor and is expressed in the medium spiny projection neurons of mouse striatum. To define the role of mGluR1 in actions of psychostimulant, we compared both motor behavior and striatal neuropeptide mRNA expression between mGluR1 mutant and wild-type control mice after a single injection of amphetamine. We found that acute amphetamine injection increased motor activity in both mutant and control mice in a dose-dependent manner (1, 4, and 12 mg/kg, i.p.). However, the overall motor responses of mGluR1 -/- mice to all three doses of amphetamine were significantly greater than those of wild-type +/+ mice. Amphetamine also induced a dose-dependent elevation of preprodynorphin mRNA in the dorsal and ventral striatum of mutant and wild-type mice as revealed by quantitative in situ hybridization. In contrast to behavioral responses, the induction of dynorphin mRNA in both the dorsal and ventral striatum of mutant mice was significantly less than that of wild-type mice in response to the two higher doses of amphetamine. In addition, amphetamine elevated basal levels of substance P mRNA in the dorsal and ventral striatum of mGluR1 mutant mice to a similar level as that of wild-type mice. There were no differences in basal levels and distribution patterns of the two mRNAs between the two genotypes of mice treated with saline. These results demonstrate a clear augmented behavioral response of mGluR1 knockout mice to acute amphetamine exposure that is closely correlated with reduced dynorphin mRNA induction in the same mice. It appears that an intact mGluR1 is specifically critical for full dynorphin induction, and impaired mobilization of inhibitory dynorphin system as a result of lacking mGluR1 may contribute to an augmentation of motor stimulation in response to acute administration of psychostimulant.

The fine organization of nigro-collicular channels with additional observations of their relationships with acetylcholinesterase in the rat

The nigro-collicular pathway that links the basal ganglia to the sensorimotor layers of superior colliculus plays a crucial role in promoting orienting behaviors. This connection originating in the pars reticulata and lateralis of the substantia nigra has been shown in rat and cat to be topographically organized. In rat, a functional compartmentalization of the substantia nigra has also been shown reflecting that of the striatum. In light of this, we reinvestigated the topographical arrangement of the nigro-collicular pathway by examining the innervation of each nigral functional zone. We performed small injections of either biocytin or wheatgerm agglutinin conjugated with horseradish peroxidase restricted to identified somatic, visual and auditory nigral zones. Frontally cut sections showed that innervations provided by the three main nigral zones form a mosaic of complementary domains stratified from the stratum opticum to the ventral part of the intermediate collicular layers, with the somatic afferents sandwiched between the visual and the auditory ones. When reconstructed from semi-horizontal sections, nigral innervations organized in the form of a honeycomb-like array composed of 100 cylindrical modules covering three-quarters of the collicular surface. Such a modular architecture is reminiscent of the acetylcholinesterase lattice we previously described in rat intermediate collicular layers. In the enzyme lattice, the surroundings of the cylindrical modules are composed of a mosaic of dense and diffuse enzyme subdomains. Thus, we compared the distribution of the overall nigral projection and of its constituent channels with the acetylcholinesterase lattice. The procedure combined axonal labelling with histochemistry on single sections for acetylcholinesterase activity. The results demonstrate that the overall nigral projection overlaps the acetylcholinesterase lattice and its constituent channels converge with either the dense or the diffuse enzyme subdomains. The stereometric arrangement of the nigro-collicular pathway is suggestive of an architecture promoting the selection of collicular motor programs for different classes of orienting behavior.

Ultrastructural evidence for differential axonal sprouting in the striatum after thermocoagulatory and aspiration lesions of the cerebral cortex in adult rats

Thermocoagulation of pial blood vessels overlying the cerebral cortex induces an ischemic degeneration of the cortex. We have previously shown with anatomical tracing techniques that thermocoagulatory lesions of the sensorimotor cortex trigger a robust axonal sprouting of contralateral cortical neurons into the denervated striatum. Similar sprouting was not observed after acute aspiration lesions of the same cortical region. We have now examined immunostaining for the growth-associated protein (GAP)-43 at the ultrastructural level after both types of lesions. A modest increase in growth cone-like structures was observed just below the corpus callosum after both lesions. However, GAP-43-positive growth cone-like structures were markedly increased in the denervated dorsolateral striatum only after thermocoagulatory lesions. In contrast, no significant increase in growth cone immunostaining was found in the dorsolateral striatum after aspiration lesions, confirming the absence of axonal sprouting in the dorsolateral striatum in this condition. Corticostriatal inputs make asymmetric synapses with dendritic spines of striatal neurons. As expected, the density of asymmetric synapses was markedly decreased in the dorsolateral striatum after aspiration lesions. However, it was not different from control after thermocoagulatory lesions that removed the same cortical area. The density of symmetric synapses was decreased after both types of lesions at 16 but not 42 days post-surgery. These data reveal that robust axonal and synaptic remodeling can occur in the dorsolateral striatum of adult rats after ischemic lesions of the cerebral cortex and further demonstrate marked differences in the degree of anatomical plasticity induced by two different types of cortical lesions.

MK-801 alters the effects of priming with L-DOPA on dopamine D1 receptor-induced changes in neuropeptide mRNA levels in the rat striatal output neurons

In a previous study, we have shown in unilaterally dopamine-depleted rats that increased behavioral responsiveness to the dopamine D1-receptor agonist SKF-38393, which was induced by pretreatment with L-DOPA, is paralleled by specific alterations in striatal neuropeptide mRNA levels. The behavioral 'priming' effect of L-DOPA is prevented if L-DOPA is preceded by the NMDA-receptor antagonist MK-801. In the present study, the question is addressed whether blockade of the increased behavioral responsiveness with MK-801 also prevents the observed changes in striatal neuropeptide mRNA levels. After a challenge with SKF-38393 (3 mg/kg, s.c.), the striatal levels of preprodynorphin, preprotachykinin, and preproenkephalin mRNA were compared between unilaterally dopamine-depleted rats that were either primed with a single administration of L-DOPA (50 mg/kg, i.p.) or with L-DOPA preceded by MK-801 (0.1 mg/kg, i.p.). Priming with L-DOPA enhanced the increase in dynorphin mRNA levels in the dorsolateral part of the dopamine-depleted striatum that occurred after SKF-38393. On the other hand, it had no significant effect on substance P or enkephalin mRNA levels. MK-801 prior to L-DOPA prevented the increased responsiveness of dynorphin regulation. However, it induced a decreased response to dopamine D1-receptor stimulation in the substance P mRNA levels in dorsal regions of the dopamine-depleted striatum. The levels of enkephalin mRNA after challenge with SKF-38393 were not affected by the MK-801 administration. These results demonstrate that the increased behavioral responsiveness to the D1-receptor agonist SKF-38393 after priming with L-DOPA is primarily related to the upregulation of dynorphin mRNA levels in the dopamine-depleted striatum.

Associative effects of Pavlovian differential inhibition of behaviour

The associative inhibitory control of behaviour is a major component of Pavlovian learning theory, but little is known about its functional neuroanatomy. The associative effects of differential inhibition of conditioned behaviour were investigated by mapping learning-related changes in brain activity of the rat with fluorodeoxyglucose autoradiography. Of interest was how a tone is processed in auditory and extra-auditory systems of the rat brain under similar behavioural, but different associative conditions. Conditioned emotional suppression to drink was used to assess training, and summation tests were used to verify that the tone became an inhibitor of conditioned behaviour. In the Inhibitor group, presentations of a tone stimulus alone were intermixed with presentations of a light stimulus followed by footshock. In the Pseudorandom group, the same numbers of tone, light and footshock presentations were used, but they were presented in a pseudorandom fashion. After training, fluorodeoxyglucose uptake was measured during tone presentations. Behavioural responding to the tone was similar during fluorodeoxyglucose uptake in the two groups, yet associative effects were found in brain activity. In the auditory system, the tone produced reduced fluorodeoxyglucose uptake in major relay nuclei (cochlear nucleus and inferior colliculus) in the Inhibitor group relative to the Pseudorandom group. The tone inhibitor produced similar decreases in the septohippocampal system and the retrosplenial cortex. In contrast, the tone inhibitor produced activity increases in somatosensory and reticulocerebellar systems. The findings provide the first detailed map of neural regions involved in the learned associations controlling differential inhibition of conditioned behaviour.

Differences in the laminar origin of projections from the medial prefrontal cortex to the nucleus accumbens shell and core regions in the rat

The medial prefrontal cortex (mPFC) projects to the nucleus accumbens shell, core and rostral pole. In this retrograde tract-tracing study of rat mPFC to nucleus accumbens projection neurons, the advantages of Neurobiotin are utilised in order to reveal the detailed morphology of labelled projection cells, and to permit an examination of the laminar projections to shell and core compartments The retrogradely transported Neurobiotin was found in somata, proximal and distal dendrites of neurons that project from the mPFC to the nucleus accumbens. The morphology of these projection neurons was revealed in great detail and confirmed that the projection arises wholly from pyramidal cells. Interestingly, it was also found that retrogradely labelled neurons were exclusively located in prelimbic and infralimbic regions in layers V and VI, after shell injections, but also in layer II following core sites. This observation may reflect possibly different roles for cortical laminae on the nucleus accumbens.

Group I metabotropic glutamate receptor activation increases phosphorylation of cAMP response element-binding protein, Elk-1, and extracellular signal-regulated kinases in rat dorsal striatum

Cyclic AMP response element-binding protein (CREB) is a major transcriptional activator at the calcium and cAMP response-element (CaCRE). Phosphorylated (p)CREB facilitates gene expression in striatal neurons. Elk-1 is another transcriptional regulator at the serum response element in the upstream promoter region of the CaCRE. Elk-1 is phosphorylated by extracellular signal-regulated kinases (ERK) and may also contribute to the regulation of gene expression. To evaluate putative roles of group I metabotropic glutamate receptors (mGluRs) in CREB, Elk-1, and ERK phosphorylation, the group I selective agonist, 3,5-dihydroxyphenylglycine (DHPG), was infused into the dorsal striatum at doses of 125, 250, or 500 nmol in freely moving rats. Semi-quantitative immunohistochemistry demonstrated that DHPG significantly increased levels of pCREB, pElk-1, and pERK immunoreactivity of ipsilateral dorsal striatum in a dose dependent manner. The increased immunoreactivity by 500 nmol DHPG was significantly blocked by intrastriatal infusion of the group I selective antagonist, n-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxamide (PHCCC, 25 nmol), but not by the group II/III antagonist, (RS)-alpha-methylserine-o-phosphate monophenyl ester (MSOPPE, 25 nmol). These data suggest that group I mGluR activation is positively linked to signaling cascades resulting in CREB, Elk-1, and ERK phosphorylation in the striatum in vivo.

Organization of corticostriatal projections from the vibrissal representations in the primary motor and somatosensory cortical areas of rodents

To characterize corticostriatal projections from rodent sensorimotor cortex, the anterograde tracers biotinylated dextran amine (BDA) and fluororuby (FR) were injected into the whisker representations of the primary motor (MI) and somatosensory (SI) cortices. Reconstructions of labeled terminals and their beaded varicosities in the neostriatum and thalamus were analyzed quantitatively to determine the degree of labeled overlap in both of these subcortical structures. Corticostriatal projections from the vibrissal representation in MI were more extensive than corresponding projections from SI. Both cortical areas sent dense projections to the dorsolateral neostriatum, but the MI vibrissal representation also projected to regions located more rostrally and medially. Despite these differences, both MI and SI projected to overlapping parts of the dorsolateral neostriatum. Tracer injections in both cortical areas also produced dense anterograde and retrograde labeling in the medial sector of the posterior complex of the thalamus (POm). Because POm is somatotopically organized and has reciprocal connections with both SI and MI cortices, the amount of labeled overlap in POm was used to indicate whether the tracers were injected into corresponding whisker representations of MI and SI. We found that the proportion of labeled overlap in the neostriatum was highly correlated with the amount of labeled overlap in POm. These results indicate that the rodent neostriatum receives convergent projections from corresponding regions in MI and SI cortex. Furthermore, the thalamocortical projections of the POm indicate that it may modulate corticostriatal outputs from corresponding representations in MI and SI.

Blockade of NMDA receptors by MK-801 reverses the changes in striatal glutamate immunolabeling in 6-OHDA-lesioned rats

A lesion of the dopamine (DA)-containing nigrostriatal pathway with 6-hydroxydopamine (6-OHDA) results in an increase in the density of nerve terminal glutamate immunolabeling and in the mean percentage of asymmetrical synapses containing a discontinuous postsynaptic density [Meshul et al. (1999) Neuroscience 88:1-16]. Similar alterations in striatal glutamate synapses have been reported following blockade of striatal DA D-2 receptors with subchronic haloperidol treatment [Meshul et al. (1994) Brain Res 648:181-195]. The haloperidol-induced change in glutamate synapses was blocked by coadministration of the N-methyl-D-aspartate (NMDA) noncompetitive receptor antagonist MK-801. In order to determine if blockade of NMDA receptors could alter the density of nerve terminal glutamate immunolabeling following a 6-OHDA lesion of the nigrostriatal pathway, MK-801 was administered to lesioned animals for 14 days. In addition, the number of apomorphine-induced contralateral rotations was determined prior to and following the administration of MK-801. MK-801 administration reversed the increase in the density of nerve terminal glutamate immunolabeling due to a 6-OHDA lesion. There was a small but significant decrease in the number of apomorphine-induced contralateral rotations following administration of MK-801 compared to the number of rotations prior to treatment with the NMDA antagonist. These results demonstrate that blockade of postsynaptic NMDA receptors affects the density of presynaptic glutamate immunolabeling and that this change in nerve terminal glutamate density is associated with a decreased behavioral response to direct DA receptor stimulation. Whether the effect of MK-801 is directly on the striatum or acts through other excitatory pathways of the basal ganglia remains unclear.

Regulation of cyclin-dependent kinase 5 and casein kinase 1 by metabotropic glutamate receptors

Cyclin-dependent kinase 5 (Cdk5) is a multifunctional neuronal protein kinase that is required for neurite outgrowth and cortical lamination and that plays an important role in dopaminergic signaling in the neostriatum through phosphorylation of Thr-75 of DARPP-32 (dopamine and cAMP-regulated phosphoprotein, molecular mass 32 kDa). Casein kinase 1 (CK1) has been implicated in a variety of cellular functions such as DNA repair, circadian rhythm, and intracellular trafficking. In the neostriatum, CK1 has been found to phosphorylate Ser-137 of DARPP-32. However, first messengers for the regulation of Cdk5 or CK1 have remained unknown. Here we report that both Cdk5 and CK1 are regulated by metabotropic glutamate receptors (mGluRs) in neostriatal neurons. (S)-3,5-dihydroxyphenylglycine (DHPG), an agonist for group I mGluRs, increased Cdk5 and CK1 activities in neostriatal slices, leading to the enhanced phosphorylation of Thr-75 and Ser-137 of DARPP-32, respectively. The effect of DHPG on Thr-75, but not on Ser-137, was blocked by a Cdk5-specific inhibitor, butyrolactone. In contrast, the effects of DHPG on both Thr-75 and Ser-137 were blocked by CK1-7 and IC261, specific inhibitors of CK1, suggesting that activation of Cdk5 by mGluRs requires CK1 activity. In support of this possibility, the DHPG-induced increase in Cdk5 activity, measured in extracts of neostriatal slices, was abolished by CK1-7 and IC261. Treatment of acutely dissociated neurons with DHPG enhanced voltage-dependent Ca(2+) currents. This enhancement was eliminated by either butyrolactone or CK1-7 and was absent in DARPP-32 knockout mice. Together these results indicate that a CK1-Cdk5-DARPP-32 cascade may be involved in the regulation by mGluR agonists of Ca(2+) channels.

Dendritic arborizations of the rat substantia nigra pars reticulata neurons: spatial organization and relation to the lamellar compartmentation of striato-nigral projections

The cerebral cortex provides a major source of inputs to the basal ganglia. As has been well documented, the topography of corticostriatal projections subdivides the striatum into a mosaic of functionally distinct sectors. How information flow from these striatal sectors remains segregated or not within basal ganglia output nuclei has to be established. Electrophysiologically identified neurons of the rat substantia nigra pars reticulata were labeled by juxtacellular injection of Neurobiotin, and the spatial organization of their dendritic arborizations was analyzed in relation to the projection fields of individual striatal sectors. Thirty-nine nigral neurons located in the projection territory of the distinct striatal sensorimotor sectors were reconstructed. The data show that the dendritic arborizations of nigral neurons conform to the geometry of striato-nigral projections. Like striatal projections, the arborizations formed a series of curved laminas enveloping a dorsolaterally located core. Although dendritic fields of the neurons lying in the laminae were flat, those located in the core were spherical or cylindrical, thereby conforming to the shape of the striatal projection fields. This remarkable alignment between the dendritic arborizations of nigral neurons and the projection fields from individual striatal districts supports the concept of a parallel architecture of the striato-nigral circuits. However, pars reticulata neurons usually extend part of their dendrites within adjacent striatal projection fields, thereby ensuring a continuum between channels. The extension of the dendritic arborizations within the striatal projection fields suggests that nigral neurons integrate the information that is relevant for the completion of the specific motor behavior they control.

Neurons in rat medial prefrontal cortex show anticipatory rate changes to predictable differential rewards in a spatial memory task

The present study electrophysiologically examined the contribution of prelimbic and infralimbic neurons in the medial prefrontal cortex (mPFC) to integration of reward and spatial information while rats performed multiple memory trials on a differentially rewarded eight arm radial maze. Alternate arms consistently held one of two different reward amounts. Similar to previous examinations of the rat mPFC, few cells showed discrete place fields or altered firing during a delay period. The most common behavioral correlate was a change in neuronal firing rate prior to reward acquisition at arm ends. A small number of reward-related cells differentiated between high and low reward arms. The presence of neurons that anticipate expected reward consequences based on information about the spatial environment is consistent with the hypothesis that the mPFC is part of a neural system which merges spatial information with its motivational significance.

Dorsal/ventral hippocampus, fornix, and conditioned place preference

Conditioned place preference (CPP) is a learning paradigm requiring formation of associations between reward and particular locations. White and McDonald (Behav Brain Res 1993;55:269-281) demonstrated that amygdala (AMG) lesions impair, while fornix (Fx) lesions enhance learning of this task. In the present experiments, we replicated the effects of AMG and Fx lesions, but we also found that complete hippocampal (HPC) lesions interfere with normal performance. Thus, the effects of Fx and HPC lesions on CPP are opposite. This is in contrast with spatial learning in the water maze. Because it has been demonstrated that damage of dorsal HPC interferes to a greater extent with spatial learning than damage of ventral HPC, we also tested animals with either dorsal or ventral HPC disruptions on CPP. Lesions limited to dorsal HPC were followed by impairment on this task. In contrast, lesions limited to ventral HPC resulted in enhanced learning. We argue that Fx and HPC lesions do not have interchangeable effects in all learning paradigms. To explain the complex pattern of results presently obtained, we propose a novel hypothesis regarding behavioral functions of HPC neural circuits. Implications regarding the interaction between memory systems are also considered.

Number, origins, and chemical types of rat pallidostriatal projection neurons

The dorsal globus pallidus (GP) receives major inputs from the dorsal neostriatum (Str), the subthalamic nucleus (STN) and the dorsal thalamus. The GP projects to multiple basal ganglia nuclei. One of the GP projection sites is the Str. The pallidostriatal projection has been considered minor. However, several recent studies have suggested that this projection is heavier than previously thought and that it might play a significant role in controlling the activity of the Str. To reveal more details of this projection, we examined the number of GP neurons that participated in the projection, their origins in the GP and their immunoreactivity for the calcium binding protein parvalbumin (PV), by using a combination of Fluoro-Gold (FG) retrograde labeling and immunohistochemical methods. Immunostaining for the calcium binding protein calbindin-28K (CaBP) was used to identify the CaBP-poor sensorimotor and CaBP-rich associative Str regions and the corresponding CaBP-poor middle, CaBP-rich border, and the caudomedial GP regions. The CaBP-poor dorsolateral Str region occupies a small portion of the Str, whereas the CaBP-poor middle GP region occupies a large portion of the GP. The immunostaining for neuron-specific nuclear protein (NeuN) was used to visualize neurons that were immunonegative for FG or PV. Cell counts revealed that the middle GP region contained a higher density of neurons and also a higher percentage of PV-positive neurons than the border and caudomedial regions of the GP. These observations suggested that the GP is involved more in sensorimotor function than associative function. Approximately 40% of neurons in the CaBP-poor middle GP region project to the CaBP-poor part of the dorsolateral Str. Approximately 30% of the neurons in both the CaBP-rich border and the caudomedial GP regions project to the CaBP-rich Str region. More than 40% of the pallidostriatal neurons in CaBP-poor middle GP region are PV-positive, whereas most of those in CaBP-rich GP regions are PV-negative. It was estimated from the cell count data that most of the PV-negative neurons in all three regions of the GP project to the Str. The results indicate that the sensorimotor and associative territories of the Str have reciprocal projections between corresponding territories of the GP. The involvement of a large number of GP neurons suggested that the pallidostriatal projection should be taken into account in the analysis of functional roles of the basal ganglia.

Differentially altered mGluR1 and mGluR5 mRNA expression in rat caudate nucleus and nucleus accumbens in the development and expression of behavioral sensitization to repeated amphetamine administration

Altered glutamatergic transmission in the striatum may be implicated in behavioral sensitization to repeated amphetamine (AMPH) administration. Quantitative in situ hybridization histochemistry was performed to define the effects of acute and chronic AMPH exposures on mRNA expression of Group I metabotropic glutamate receptors (mGluRs) in the striatum. Behavioral ratings indicated that the motor activity of rats was significantly higher after the final of five daily AMPH injections (4 mg/kg, i.p.) than that after the first of five daily AMPH, indicative of the development of behavioral sensitization. Moreover, the motor activity of rats treated with five daily AMPH was significantly greater than that of rats treated with five daily saline in response to a 2 mg/kg challenge dose of AMPH 7, 14, 28, and 60 days after the discontinuation of drug treatments, indicative of the persistent expression of behavioral sensitization. Three hours after acute administration of AMPH to naive rats, mGluR1 and mGluR5 mRNA expression in the dorsal (caudatoputamen) and ventral (nucleus accumbens) striatum showed no change as compared to acute saline injection. In rats that developed behavioral sensitization to repeated AMPH, mGluR1 levels in the dorsal and ventral striatum were increased by 53% and 43%, respectively, 3 h after the final AMPH treatment. However, this change did not persist during withdrawal since it was not observed 7, 14, and 28 days after the discontinuation of AMPH treatment. Conversely, mGluR5 levels were markedly reduced 3 h after the final of five daily AMPH treatments in the entire striatum of sensitized rats (34% and 77% of controls in the dorsal and ventral striatum, respectively). The reduction persisted at 7, 14, and 28 days of withdrawal. These results reveal a close linkage between striatal Group I mGluR gene expression and behavioral sensitization to AMPH. This may indicate functional implications of the two subtypes of Group I mGluRs in the regulation of behavioral sensitization to the dopamine stimulant.

Effects of dorsal-striatum lesions and fimbria-fornix lesions on the problem-solving strategies of rats in a shallow water maze

In solving a spatial problem, animals can use a place, cue, or response strategy. The present research was designed to evaluate the role of dorsal striatum (DS) in spatial problem solving and to compare it with that of fimbria fornix (FF). Rats were trained with a place + cue task in a shallow pool, then were divided into three groups (DS, FF, control), and lesions were made in the corresponding areas. After retraining, four probe tests were given: Test 1 (start position moved), Test 2 (goal and start positions moved), Test 3 (invisible goal), and Test 4 (curtain test). The test results suggest that the DS and Control groups performed the original task by using the place strategy, whereas the FF group used the cue strategy, which strongly implies that the DS group was impaired in the use of the cue strategy. This research also provides evidence supporting the usefulness of a shallow pool in evaluating animal behavior.

Use of win-stay and win-shift strategies in place and cue tasks by medial caudate putamen (MCPu) lesioned rats

This study investigated the behavioral function of the medial caudate putamen (MCPu) in the solving of maze tasks. MCPu lesioned rats (n = 35) and control rats (n = 35) were trained for the place or cue task (the four baited arms and four unbaited arms task) in an eight-arm radial maze, which requires the win-stay or the win-shift strategy. In Experiment 1, in which the place task was used, MCPu lesioned rats could learn the task in the win-shift condition, but not in the win-stay condition. MCPu lesioned rats made a lot of unbaited errors in the win-stay condition, as they persistently chose adjacent arms. Control rats could learn the tasks in both conditions. In Experiment 2, in which the cue task was used, MCPu lesioned rats and control rats could learn the tasks in both the win-stay and the win-shift conditions. If anything, the performance of MCPu rats was a little better than that of control rats in the win-stay condition. The results of these two experiments revealed that the MCPu was involved in solving the win-stay place task, but not the win-shift place, win-stay cue, and win-shift cue tasks. These findings suggest that the MCPu plays an important role in utilizing both spatial information and switching foraging strategies flexibly and efficiently, that is, processing complicated visuospatial cognition.