Mesolimbic dopaminergic neurones in the rotational model of nigrostriatal function

Synergistic Nigral Output Pathways Shape Movement

Locomotion relies on the activity of basal ganglia networks, where, as the output, the substantia nigra pars reticulata (SNr) integrates incoming signals and relays them to downstream areas. The cellular and circuit substrates of such a complex function remain unclear. We hypothesized that the SNr controls different aspects of locomotion through coordinated cell-type-specific sub-circuits. Using anatomical mapping, single-cell qPCR, and electrophysiological techniques, we identified two SNr sub-populations: the centromedial-thalamo projectors (CMps) and the SN compacta projectors (SNcps), which are genetically targeted based on vesicular transporter for gamma-aminobutyric acid (VGAT) or parvalbumin (PV) expression, respectively. Optogenetic manipulation of these two sub-types across a series of motor tests provided evidence that they govern different aspects of motor behavior. While CMp activity supports the continuity of motor patterns, SNcp modulates the immediate motor drive behind them. Collectively, our data suggest that at least two different sub-circuits arise from the SNr, engage different behavioral motor components, and collaborate to produce correct locomotion.

The Amphetamine Induced Rotation Test: A Re-Assessment of Its Use as a Tool to Monitor Motor Impairment and Functional Recovery in Rodent Models of Parkinson's Disease

Rats and mice with unilateral damage to the nigrostriatal dopamine system—induced by neurotoxins, such as 6-hydroxydopamine, overexpression of α-synuclein, or injections of toxic synuclein protofibrils—are widely used as experimental models to mimic the loss of dopamine neurons seen in Parkinson’s disease. The amphetamine rotation test is commonly used to monitor the extent of motor impairment induced by the lesion, and this test has also become the standard tool to demonstrate transplant-induced functional recovery or the efficacy of neuroprotective interventions aimed to preserve or restore DA neuron function. Although the amphetamine-induced rotation test is highly useful for this purpose it has some important pitfalls and the interpretation of the data may not always be straightforward. Unless the test is applied properly and the data are displayed and interpreted appropriately the conclusions may be misleading or simply totally wrong. The purpose of this review is to draw attention to the potential problems and pitfalls involved in the use of drug-induced rotation tests, and to provide recommendations and advice on how to avoid them.

What does dopamine mean?

Dopamine is a critical modulator of both learning and motivation. This presents a problem: how can target cells know whether increased dopamine is a signal to learn or to move? It is often presumed that motivation involves slow ('tonic') dopamine changes, while fast ('phasic') dopamine fluctuations convey reward prediction errors for learning. Yet recent studies have shown that dopamine conveys motivational value and promotes movement even on subsecond timescales. Here I describe an alternative account of how dopamine regulates ongoing behavior. Dopamine release related to motivation is rapidly and locally sculpted by receptors on dopamine terminals, independently from dopamine cell firing. Target neurons abruptly switch between learning and performance modes, with striatal cholinergic interneurons providing one candidate switch mechanism. The behavioral impact of dopamine varies by subregion, but in each case dopamine provides a dynamic estimate of whether it is worth expending a limited internal resource, such as energy, attention, or time.

Transplantation site influences the phenotypic differentiation of dopamine neurons in ventral mesencephalic grafts in Parkinsonian rats

Foetal midbrain progenitors have been shown to survive, give rise to different classes of dopamine neurons and integrate into the host brain alleviating Parkinsonian symptoms following transplantation in patients and animal models of the disease. Dopamine neuron subpopulations in the midbrain, namely A9 and A10, can be identified anatomically based on cell morphology and ascending axonal projections. G protein-gated inwardly rectifying potassium channel Girk2 and the calcium binding protein Calbindin are the two best available histochemical markers currently used to label (with some overlap) A9- and A10-like dopamine neuron subtypes, respectively, in tyrosine hydroxylase expressing neurons both in the midbrain and grafts. Both classes of dopamine neurons survive in grafts in the striatum and extend axonal projections to their normal dorsal and ventral striatal targets depending on phenotype. Nevertheless, grafts transplanted into the dorsal striatum, which is an A9 input nucleus, are enriched for dopamine neurons that express Girk2. It remains to be elucidated whether different transplantation sites favour the differential survival and/or development of concordant dopamine neuron subtypes within the grafts. Here we used rat foetal midbrain progenitors at two developmental stages corresponding to a peak in either A9 or A10 neurogenesis and examined their commitment to respective dopaminergic phenotypes by grafting cells into different forebrain regions that contain targets of either nigral A9 dopamine innervation (dorsal striatum), ventral tegmental area A10 dopamine innervation (nucleus accumbens and prefrontal cortex), or only sparse dopamine but rich noradrenaline innervation (hippocampus). We demonstrate that young (embryonic day, E12), but not older (E14), mesencephalic tissue and the transplant environment influence survival and functional integration of specific subtypes of dopamine neurons into the host brain. We also show that irrespective of donor age A9-like, Girk2-expressing neurons are more responsive to environmental cues in adopting a dopaminergic phenotype during differentiation post-grafting. These novel findings suggest that dopamine progenitors use targets of A9/A10 innervation in the transplantation site to complete maturation and the efficacy of foetal cell replacement therapy in patients may be improved by deriving midbrain tissue at earlier developmental stages than in current practice.

Generative rules of Drosophila locomotor behavior as a candidate homology across phyla

The discovery of shared behavioral processes across phyla is a significant step in the establishment of a comparative study of behavior. We use immobility as an origin and reference for the measurement of fly locomotor behavior; speed, walking direction and trunk orientation as the degrees of freedom shaping this behavior; and cocaine as the parameter inducing progressive transitions in and out of immobility. We characterize and quantify the generative rules that shape Drosophila locomotor behavior, bringing about a gradual buildup of kinematic degrees of freedom during the transition from immobility to normal behavior, and the opposite narrowing down into immobility. Transitions into immobility unfold via sequential enhancement and then elimination of translation, curvature and finally rotation. Transitions out of immobility unfold by progressive addition of these degrees of freedom in the opposite order. The same generative rules have been found in vertebrate locomotor behavior in several contexts (pharmacological manipulations, ontogeny, social interactions) involving transitions in-and-out of immobility. Recent claims for deep homology between arthropod central complex and vertebrate basal ganglia provide an opportunity to examine whether the rules we report also share common descent. Our approach prompts the discovery of behavioral homologies, contributing to the elusive problem of behavioral evolution.

Modulation of locomotor activation by the rostromedial tegmental nucleus

The rostromedial tegmental nucleus (RMTg) is a strong inhibitor of dopamine neurons in the ventral tegmental area (VTA) reported to influence neurobiological and behavioral responses to reward omission, aversive and fear-eliciting stimuli, and certain drugs of abuse. Insofar as previous studies implicate ventral mesencephalic dopamine neurons as an essential component of locomotor activation, we hypothesized that the RMTg also should modulate locomotion activation. We observed that bilateral infusions into the RMTg of the gamma-aminobutyric acid A (GABAA) agonist, muscimol, indeed activate locomotion. Alternatively, bilateral RMTg infusions of the GABAA receptor antagonist, bicuculline, suppress robust activations of locomotion elicited in two distinct ways: (1) by disinhibitory stimulation of neurons in the lateral preoptic area and (2) by return of rats to an environment previously paired with amphetamine administration. The possibility that suppressive locomotor effects of RMTg bicuculline infusions were due to unintended spread of drug to the nearby VTA was falsified by a control experiment showing that bilateral infusions of bicuculline into the VTA produce activation rather than suppression of locomotion. These results objectively implicate the RMTg in the regulation of locomotor activation. The effect is important because much evidence reported in the literature suggests that locomotor activation can be an involuntary behavioral expression of expectation and/or want without which the willingness to execute adaptive behaviors is impaired.

Control of the nigrostriatal dopamine neuron activity and motor function by the tail of the ventral tegmental area

Midbrain dopamine neurons are implicated in various psychiatric and neurological disorders. The GABAergic tail of the ventral tegmental area (tVTA), also named the rostromedial tegmental nucleus (RMTg), displays dense projections to the midbrain and exerts electrophysiological control over dopamine cells of the VTA. However, the influence of the tVTA on the nigrostriatal pathway, from the substantia nigra pars compacta (SNc) to the dorsal striatum, and on related functions remains to be addressed. The present study highlights the role played by the tVTA as a GABA brake for the nigrostriatal system, demonstrating a critical influence over motor functions. Using neuroanatomical approaches with tract tracing and electron microscopy, we reveal the presence of a tVTA-SNc-dorsal striatum pathway. Using in vivo electrophysiology, we prove that the tVTA is a major inhibitory control center for SNc dopamine cells. Using behavioral approaches, we demonstrate that the tVTA controls rotation behavior, motor coordination, and motor skill learning. The motor enhancements observed after ablation of the tVTA are in this regard comparable with the performance-enhancing properties of amphetamine, a drug used in doping. These findings demonstrate that the tVTA is a major GABA brake for nigral dopamine systems and nigrostriatal functions, and they raise important questions about how the tVTA is integrated within the basal ganglia circuitry. They also warrant further research on the tVTA's role in motor and dopamine-related pathological contexts such as Parkinson's disease.

Neural structures mediating expression and extinction of platform-mediated avoidance

Individuals use both passive and active defensive responses to environmental threats. Much is known about the neural circuits of passive defensive responses (e.g., freezing), but less is known about the substrates of active defensive responses (e.g., avoidance). We developed an active avoidance task in which rats learn to avoid a tone-signaled footshock by stepping onto a nearby platform. An advantage of this task is that freezing, which can interfere with avoidance, is reduced, thereby facilitating comparison of the effects of manipulations on avoidance versus freezing. After 10 d of avoidance training, rats were infused with muscimol to pharmacologically inactivate the prelimbic cortex (PL), infralimbic cortex (IL), ventral striatum (VS), or basolateral amygdala (BLA). Inactivating PL, VS, or BLA all impaired avoidance expression, but these areas differed with respect to freezing. Inactivating BLA decreased freezing consistent with loss of the tone-shock association, whereas inactivation of VS increased freezing consistent with loss of avoidance memory. Inactivation of PL had no effect on freezing. Inactivation of IL did not impair avoidance expression but did impair avoidance extinction. Our findings suggest that active avoidance is mediated by prefrontal-striatal circuits, which may be overactive in individuals suffering from trauma-related disorders.

The PKC inhibitor Ro31-8220 blocks acute amphetamine-induced dopamine overflow in the nucleus accumbens

Acute administration of the psychostimulant amphetamine increases extracellular levels of dopamine (DA) by reversing the DA transporter on ascending midbrain DA neurons. In vitro studies using striatal synaptosomal, slice and nucleus accumbens (NAcc) tissue preparations have implicated protein kinase C (PKC) in this effect. The present study further examined this effect in vivo by assessing the ability of the PKC inhibitor, Ro31-8220 (10 microM), to inhibit acute amphetamine-induced DA overflow when applied with this drug to the NAcc via reverse dialysis. Amphetamine was applied at a concentration of 30 microM, and the core and shell subregions of the NAcc were assayed separately in freely moving rats. These brain regions play a role in the acute locomotor-activating and motivational effects of amphetamine. Consistent with the findings of previous in vitro experiments, reverse dialysis of Ro31-8220 with amphetamine robustly attenuated the ability of this drug to increase extracellular levels of dopamine in both the core and shell subregions of the NAcc. These results confirm that amphetamine stimulates dopamine overflow via a PKC-dependent mechanism.

The Corridor Task: A simple test of lateralised response selection sensitive to unilateral dopamine deafferentation and graft-derived dopamine replacement in the striatum

In this experiment, we report a novel drug-free behavioural test of lateralised neglect which is sensitive to unilateral dopamine-denervating lesions and subsequent graft-derived striatal dopamine replacement. For the task, white plastic lids containing sugar pellets were placed along the left and right sides of the floor of a long narrow corridor at regular intervals. Hungry female Sprague-Dawley rats were placed individually into the corridor where they were allowed to make up to 20 pellet retrievals. The number of retrievals each rat made from its left and right sides was counted. Complete mesencephalic or partial nigrostriatal lesions were induced by injection of 6-hydroxydopamine into the medial forebrain bundle or striatum, respectively. Both lesions induced a pronounced ipsilateral retrieval bias in the task. Five weeks after lesion surgery, half of the rats from each lesion group were given E14 ventral mesencephalic cell suspension transplants into the denervated striatum, and were then re-tested in the Corridor Task 5 and 10 weeks later. There was no amelioration of the side bias in rats with medial forebrain bundle lesions. In contrast, in nigrostriatal-lesioned rats, the graft significantly reduced the lesion-induced ipsilateral bias. We conclude that the Corridor Task is a sensitive test of lateralised sensorimotor response selection, and is suitable for assessing deficits and recovery associated with lesions and grafts within the nigrostriatal system.

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

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

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

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

Parkinsonian motor deficits are reflected by proportional A9/A10 dopamine neuron degeneration in the rat

In a model of Parkinson's disease (PD), amphetamine, a dopamine (DA)-releasing drug, fails to induce ipsilateral drug rotations in a proportion of rats with complete unilateral 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle and DA neurons of the substantia nigra. To investigate this phenomenon, individual 6-OHDA lesions (measured by tyrosine hydroxylase immunohistochemistry) in the substantia nigra pars compacta (A9), ventral tegmental area (A10), and striatum were examined in conjunction with outcomes of four behavioral tests. The behavioral tests were skilled paw reaching, a head-turning test, and apomorphine (0.05 mg/kg) and amphetamine (4 mg/kg) drug-induced rotations. Four weeks postlesion, ipsilateral side bias measured by the head-turning test correlated strongly with extent of A9 DA neuronal lesion. Additional A10 neuronal DA lesions did not substantially improve the model fit, indicating that the head-turning bias was primarily A9 dependent. In contrast, total head-turning activity increased monotonically with lesions of A10 striatal DA fibers. Skilled paw-reaching accuracy decreased with increased lesion of both A9 and A10 DA neuronal systems. Associating amphetamine-induced rotations with extent of A9 DA lesion generated a second-order polynomial model, y = -11.1x + 0.20 x(2) + 208.7 (R(2) = 0.73), with an overall F ratio (df = 2,21) of 28.4 (P < 0.0001). This model predicts that an A9 DA lesion of about 50% is required to induce an ipsilateral turning bias, after which rotations increase with the degree of A9 DA neuronal lesion. No further change in rotational behavior was seen until an additional A10 DA lesion reached 60%, after which the rotational response decreased. This analysis provides tests that differentiate between A9 DA degeneration and combined A9/A10 lesions in animal models and in addition allows predictive testing of PD therapeutic intervention at a preclinical level.

Effect of intracerebral administration of NMDA and AMPA on dopamine and glutamate release in the ventral pallidum and on motor behavior

The present study investigates the modulation of the ventral tegmental area (VTA)-ventral pallidum (VP) dopaminergic system by glutamate agonists in rats. The glutamate receptor agonists N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were infused via reversed microdialysis into the VTA, and dopamine (DA), glutamate, and aspartate levels in the VTA and ipsilateral VP were monitored together with motor behavior screened in an open field. NMDA (750 microM) infusion, as well as AMPA (50 microM) infusion, induced an increase of DA and glutamate levels in the VTA, followed by an increase of DA levels in the ipsilateral VP and by enhanced locomotor activity. The increase of DA in the VP was similar after administration of these two glutamate agonists, although motor activity was more pronounced and showed an earlier onset after NMDA infusion. Glutamate levels in the VP were not increased by the stimulation of DA release. It is concluded that DA is released from mesencephalic DA neurons projecting to the VP and that these neurons are controlled by glutamatergic systems, via NMDA and AMPA receptors. Thus, DA in the VP has to be considered as a substantial modulator. Dysregulation of the mesopallidal DA neurons, as well as their glutamatergic control, may play an additional or distinct role in disorders like schizophrenia and drug addiction.

Behavioural and neurochemical effects of cholinergic and dopaminergic agonists administered into the accumbal core and shell in rats

The first goal of this study was to investigate whether turning behaviour elicited by unilateral injections of the cholinergic agonist carbachol into the shell of the nucleus accumbens differs from that elicited by similar injections into the core of this nucleus, and to compare the behavioural effects with the known effects of such injections of the mixture of the dopamine D1 and D2 receptor agonists SKF 38393 (5 microg) and quinpirole (10 microg). The second goal was to investigate whether these injections of carbachol produce neurochemical alterations in the ventrolateral striatum that differ from similar injections of the mixture of the dopamine D1 and D2 receptor agonists into these brain regions. Injections of carbachol into the shell produced predominantly (a) contralateral circling marked by normal stepping and running in wide circles during the initial 50 min and (b) postural asymmetry during the following 75 min; similar injections into the core produced (a) contralateral pivoting, namely pathological head-to-tail turning marked by abnormal hindlimb stepping during the initial 50 min and (b) postural asymmetry during the next 75 min. The postural asymmetry seen after the carbachol injections was closely associated with the drug-induced increase in the dopamine release measured by microdialysis in the ipsilateral striatum. Injections of the mixture of dopamine agonists into the shell, but not core, also produced pivoting. These shell injections increased the dopamine release in the ipsilateral striatum, and decreased it in the contralateral striatum. The relative increase in the ipsilateral striatum was closely associated with the drug-induced pivoting. The data show that stimulation of cholinergic and dopaminergic receptors in the shell and core elicit effects that vary according to the subregion of the nucleus accumbens. It is concluded that the accumbens-specific, cholinergic effects are mediated via substrates that differ from those involved in the shell-specific, dopaminergic effects.

Associative processes in addiction and reward. The role of amygdala-ventral striatal subsystems

Only recently have the functional implications of the organization of the ventral striatum, amygdala, and related limbic-cortical structures, and their neuroanatomical interactions begun to be clarified. Processes of activation and reward have long been associated with the NAcc and its dopamine innervation, but the precise relationships between these constructs have remained elusive. We have sought to enrich our understanding of the special role of the ventral striatum in coordinating the contribution of different functional subsystems to confer flexibility, as well as coherence and vigor, to goal-directed behavior, through different forms of associative learning. Such appetitive behavior comprises many subcomponents, some of which we have isolated in these experiments to reveal that, not surprisingly, the mechanisms by which an animal sequences responding to reach a goal are complex. The data reveal how the different components, pavlovian approach (or sign-tracking), conditioned reinforcement (whereby pavlovian stimuli control goal-directed action), and also more general response-invigorating processes (often called "activation," "stress," or "drive") may be integrated within the ventral striatum through convergent interactions of the amygdala, other limbic cortical structures, and the mesolimbic dopamine system to produce coherent behavior. The position is probably not far different when considering aversively motivated behavior. Although it may be necessary to employ simplified, even abstract, paradigms for isolating these mechanisms, their concerted action can readily be appreciated in an adaptive, functional setting, such as the responding by rats for intravenous cocaine under a second-order schedule of reinforcement. Here, the interactions of primary reinforcement, psychomotor activation, pavlovian conditioning, and the control that drug cues exert over the integrated drug-seeking response can be seen to operate both serially and concurrently. The power of our analytic techniques for understanding complex motivated behavior has been evident for some time. However, the crucial point is that we are now able to map these components with increasing certainty onto discrete amygdaloid, and other limbic cortical-ventral striatal subsystems. The neural dissection of these mechanisms also serves an important theoretical purpose in helping to validate the various hypothetical constructs and further developing theory. Major challenges remain, not the least of which is an understanding of the operation of the ventral striatum together with its dopaminergic innervation and its interactions with the basolateral amygdala, hippocampal formation, and prefrontal cortex at a more mechanistic, neuronal level.

Dissociation in effects of lesions of the nucleus accumbens core and shell on appetitive pavlovian approach behavior and the potentiation of conditioned reinforcement and locomotor activity by D-amphetamine

Dopamine release within the nucleus accumbens (NAcc) has been associated with both the rewarding and locomotor-stimulant effects of abused drugs. The functions of the NAcc core and shell were investigated in mediating amphetamine-potentiated conditioned reinforcement and locomotion. Rats were initially trained to associate a neutral stimulus (Pavlovian CS) with food reinforcement (US). After excitotoxic lesions that selectively destroyed either the NAcc core or shell, animals underwent additional CS-US training sessions and then were tested for the acquisition of a new instrumental response that produced the CS acting as a conditioned reinforcer (CR). Animals were infused intra-NAcc with D-amphetamine (0, 1, 3, 10, or 20 microg) before each session. Shell lesions affected neither Pavlovian nor instrumental conditioning but completely abolished the potentiative effect of intra-NAcc amphetamine on responding with CR. Core-lesioned animals were impaired during the Pavlovian retraining sessions but showed no deficit in the acquisition of responding with CR. However, the selectivity in stimulant-induced potentiation of the CR lever was reduced, as intra-NAcc amphetamine infusions dose-dependently increased responding on both the CR lever and a nonreinforced (control) lever. Shell lesions produced hypoactivity and attenuated amphetamine-induced activity. In contrast, core lesions resulted in hyperactivity and enhanced the locomotor-stimulating effect of amphetamine. These results indicate a functional dissociation of subregions of the NAcc; the shell is a critical site for stimulant effects underlying the enhancement of responding with CR and locomotion after intra-NAcc injections of amphetamine, whereas the core is implicated in mechanisms underlying the expression of CS-US associations.

Destruction of the noradrenergic system with DSP4 potentiates the behavioral effects of MK-801 in rats

In this study we investigated the effect of lesioning the noradrenergic systems on the behavioral effects of (5R, 10S)-(+)-5-Methyl-10,11-dihydro-5H-dibenzo [a, d] cyclohepten-5,10-imine hydrogen maleate--MK-801, in rats. The noradrenergic system was lesioned with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride--DSP4 (60 mg/kg IP). MK-801 increased the locomotor activity and rearing. DSP4 significantly further increased the hyperlocomotor activity, circling (especially to the left side), sniffing, rolling, and falling that were induced by MK-801. These results showed that destruction of the noradrenergic system increased MK-801-hyperlocomotor activity, ataxia and stereotypy.

Injection of the protein kinase C inhibitor Ro31-8220 into the nucleus accumbens attenuates the acute response to amphetamine: tissue and behavioral studies

The ability of amphetamine to produce heightened locomotor activity is thought to be due to its ability to enhance dopamine release from mesolimbic dopamine neurons. The mechanism by which amphetamine increases dopamine release is not well understood, but is thought to involve exchange diffusion with synaptosomal dopamine through the dopamine transporter. We recently reported that amphetamine-mediated dopamine release in the striatum is also dependent on protein kinase C activity. In the current study, we investigated the role of protein kinase C activity in the acute neurochemical and behavioral response to amphetamine in the nucleus accumbens. Consistent with previous results in the striatum, amphetamine-stimulated dopamine release from nucleus accumbens tissue was inhibited by the specific protein kinase C inhibitor Ro31-8220, but not by the relatively inactive analog bisindoylmaleimide V. In addition, the effects of protein kinase C activity on the acute behavioral response to amphetamine was examined by injecting Ro31-8220 into the nucleus accumbens 15 min prior to intra-accumbens amphetamine. Pretreatment with Ro31-8220 attenuated the motor-stimulant effects of intra-accumbens amphetamine relative to control subjects pretreated with vehicle. Bisindoylmaleimide V did not significantly inhibit the motor-stimulant effects of intra-accumbens amphetamine. These results suggest that the action of amphetamine in the nucleus accumbens in increasing dopamine release and locomotor activity is dependent on protein kinase C activity.

Ibogaine effects on sweet preference and amphetamine induced locomotion: implications for drug addiction

The neural basis of ibogaine's effects on drug-related behaviours is unclear. One possibility is that ibogaine interferes with the shared capacity of many addictive agents to stimulate brain dopamine activity, but reports of ibogaine effects on dopamine activity have been inconsistent. Our study suggests such inconsistencies may result from variations in prior drug exposure. If ibogaine blocks dopamine activity, then it should, like dopamine blockers, decrease preference for natural rewards such as sweet solutions. However, 40 mg/kg ibogaine i.p. did not decrease preference for a glucose + saccharin solution when it was administered to male Long Evans rats 24 h prior to test in Experiment 1. Nor did ibogaine attenuate conditioned preference for a neutral flavour previously paired with sweet taste in Experiment 2. In Experiment 3, effects of 40 mg/kg ibogaine on amphetamine-induced locomotion were investigated in drug-naive and drug-experienced (four prior doses of 1.5 mg/kg amphetamine) rats. Locomotion was significantly lower in those ibogaine-treated rats that had previously been exposed to amphetamine than in those that had not. Thus, ibogaine may serve to decrease induced levels of dopamine activity in drug-experienced animals or humans from elevated, sensitized levels back to baseline levels. This could lead to a reduction of sensitized levels of drug craving in addiction.

Morphological and biochemical adaptations to unilateral dopamine denervation of the neostriatum in newborn rats

Basal ganglia of adult rats were examined for morphological and biochemical changes resulting from neonatal unilateral dopamine denervation of the striatum with increasing doses of 6-hydroxydopamine (4, 12 and 20 microg). Rotational behaviour induced by apomorphine (0.1 mg/kg) was observed in all rats injected with the high dose (20 microg) and totally absent in those injected with the low dose (4 microg). As assessed with tyrosine hydroxylase immunocytochemistry, the extent of dopamine denervation within the injected striatum was clearly related to the dose injected. In the mesencephalon, losses of tyrosine hydroxylase-immunoreactive cell bodies were proportional to the dose injected and the extent of neostriatal dopamine denervation. This retrograde cell loss predominated in the ventromedial and lateral parts of the substantia nigra pars compacta, with relative sparing of the ventral tegmental area. After the injection of the intermediate (12 microg) and the high (20 microg) doses, a network of thin tyrosine hydroxylase-immunoreactive fibres was visualized in the ventral part of the pars reticulata ipsilateral to the injected striatum, suggesting a neoinnervation of this structure by dopamine axons. After the high dose, the density of serotonin-immunoreactive fibres was enhanced in the anterior half of the lesioned striatum. Associated changes in dopamine and serotonin content and turnover were also documented on both sides, in the striatum and in two output structures of the basal ganglia, the globus pallidus and the substantia nigra. Dopamine content was decreased only on the injected side. After the low dose, equal reductions (-60%) were observed in the anterior striatum and the substantia nigra, whereas a more marked decrease was measured in the anterior striatum (-93%) than in the substantia nigra (-60% to -74%) after the intermediate and high doses. In the globus pallidus, dopamine tissue content was decreased (-51%) only after the high dose. Dopamine turnover was unchanged after the low dose in all structures examined and was increased in the striatum, on the lesioned side only, after the intermediate and high doses. Serotonin content was increased only on the injected side in the anterior striatum (+50% after the low and +92% after the high dose). Serotonin turnover was unchanged on the injected side but increased by +118% and by +81% in the contralateral anterior striatum after the low and high doses, respectively. It was also increased in both substantia nigra after the high dose. In conclusion, morphological changes similar to those described after a bilateral neonatal lesion were observed on the injected side in the model of the unilateral neonatal nigrostriatal dopamine denervation. Biochemical changes were, however, not restricted to the lesioned side. Notably, changes in serotonin turnover developed on the contralateral side. These morphological and biochemical adaptative changes need to be taken into account in considering the mechanisms implicated in the rotional behaviour measured in these animals.

Comparison of the effects of prototypical behavioral stimulants on locomotor activity and rotational behavior in rats

The present study was performed to characterize on rotational behavior the dose- and time-effect relationship of four prototypical behavioral stimulants that interact with dopamine systems via different mechanisms of action. Drug effects on rotational behavior was compared with effects on locomotor activity. The drugs examined were apomorphine (0.03-1.0 mg/kg), d-amphetamine (0.1-3.0 mg/kg), cocaine (3.0-56 mg/kg), and caffeine (10-100 mg/kg). SKF-38393 (0.3-10 mg/kg), a dopamine receptor agonist that has only modest effects on locomotor activity, was tested as a comparison. In rats with unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the nigrostriatal tract, d-amphetamine and cocaine dose dependently increased both the duration and the maximum number of turns/10 min, whereas apomorphine and caffeine increased only the duration of turning. There was a significant correlation of the effects of the four drugs on rotational behavior with effects on locomotor activity, but effects across drugs were not identical. Dose-response curves revealed potency differences among drugs in their effects on the two behaviors (e.g., apomorphine stimulated rotational behavior at a lower dose than it stimulated locomotor activity, whereas the converse was true with caffeine). Different mechanisms of action of these drugs might account for the differences in their effects on these behaviors.

Stimulation of acetylcholine or dopamine receptors in the nucleus accumbens differentially alters dopamine release in the striatum of freely moving rats

The present study examined whether unilateral stimulation of acetylcholine or dopamine receptors in the nucleus accumbens induces an asymmetry in dopamine transmission in the ventrolateral striatum. For this purpose, a microdialysis technique was used to measure dopamine release in both sides of the ventrolateral striatum following unilateral injections of carbachol (5 micrograms/0.5 microliter) or a mixture of dopamine D1 and dopamine D2 receptor agonists (1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine-7,8-diol 5 micrograms + quinpirole 10 micrograms/0.5 microliter) into the nucleus accumbens. The results show that carbachol injection increased dopamine release in the ipsilateral striatum without changing dopamine release in the contralateral striatum, whereas the dopamine D1/D2 receptor agonist mixture injected unilaterally into the nucleus accumbens produced an increase followed by a decrease in dopamine release in the ipsilateral striatum, but only a decrease in dopamine release in the contralateral striatum. The biochemical effects of the cholinergic treatment greatly outlasted the drug-induced contralateral turning, whereas the biochemical effects of the dopaminergic treatment showed a good correlation with the drug-induced contralateral turning. The present study provides biochemical evidence that unilateral stimulation of acetylcholine or dopamine receptors in the nucleus accumbens elicits an asymmetry in dopaminergic activity in the ventrolateral striatum. The present study also provides biochemical evidence that two distinct neural substrates are involved in the effects of cholinergic and dopaminergic manipulation of the nucleus accumbens.

The placement of a striatal ibotenic acid lesion affects skilled forelimb use and the direction of drug-induced rotation

The motor consequences of excitotoxic striatal damage have been evaluated extensively in the rat, using tests of whole body motor asymmetry and of deficits in skilled paw and limb movements. However conflicting results of both the type and extent of behavioural deficits have been reported, particularly in the direction of rotation observed in response to the dopamine receptor agonist, apomorphine. The present study investigated the effect of unilateral ibotenic acid lesions in the dorsal striatum of the adult rat, placed at either anterior, posterior, medial, or lateral loci, on rotation in response to both amphetamine and apomorphine, and in the "staircase test" of skilled forelimb use. In a 2 x 2 matrix design experiment, adult female albino rats received a double unilateral lesion of 0.5 microliter 0.06 M ibotenic acid injected at each of two sites either anterior (medial and lateral), posterior (medial and lateral), medial (anterior and posterior), or lateral (anterior and posterior). Rats that received posterior lesions showed a marked ipsilateral rotation in response to both amphetamine and apomorphine, while animals receiving anterior lesions showed little ipsilateral or a slight contralateral bias. Rats receiving lateral lesions showed a marked impairment of contralateral paw use on the "staircase test," while animals with medial lesions showed no significant difference to control unoperated animals. These results confirm the somatotopic organisation of the dorsal striatum in its control of motor functions, and indicate the need to take into account the locus of an excitotoxic lesion in the design of lesion and transplantation studies if we are to achieve reliable tests of the behavioural deficits and recovery.

Impairments and compensatory adjustments in spontaneous movement after unilateral dopamine depletion in rats

Rats with unilateral dopamine (DA) depletions (hemi-Parkinson rats) display directional biases in their locomotion in spontaneous and drug induced tests. These biases have been explained as being due either to changed responsiveness to sensory stimulation, changes in motor ability, or to central changes, but as yet their basis is not fully understood. The purpose of the present experiment is to examine the posture of immobility and the posture and strategies of locomotion in rats with unilateral DA depletions. The rats are found to display impairments in their bad limbs (contralateral-to-lesion limbs) in adjusting posture and moving. They compensate by supporting themselves mainly on their good hindlimb, using the bad hindlimb and tail for balance and by disproportionately relying upon their good limbs to turn and to walk. Thus, their center of gravity is shifted to the good side and movement is preferentially directed toward the good side, in part to maintain equilibrium and in part to remove weight from the bad limbs so that they can enter the swing phase of the stepping cycle. It is proposed that the bad limbs may be unable to apply force to adjust posture and produce movement. These results provide a basis for predicting the movements that the animals will use in various situations and they expand the test repertoire this hemi-Parkinson model provides for studying recovery processes after loss of dopamine.

Dissimilarities between cholinergic and dopaminergic turning elicited by nucleus accumbens stimulation in freely moving rats

Contralateral turning was produced by unilateral injection of carbachol (0.5, 2.5, 5 micrograms) into the nucleus accumbens, but not into the dorsal or ventral striatum. This behaviour was inhibited by muscarinic M1 acetylcholine receptor blockade in the nucleus accumbens, and less effectively by blockade of muscarinic M2 and nicotinic acetylcholine receptors. Unilateral injection of a mixture of the dopamine D1 receptor agonist 1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 38393, 5 micrograms) and the dopamine D2 receptor agonist quinpirole (10 micrograms) also produced contralateral turning. The stepping pattern, however, completely differed from that induced by carbachol. The number of carbachol-induced turnings was reduced by dopamine D1 or D2 receptor blockade (8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol (SCH 23390) and l-sulpiride, respectively) in the nucleus accumbens. However, the reduction was due to a change in the turning pattern. Blockade of muscarinic acetylcholine receptors in the nucleus accumbens did not change the contralateral turning induced by unilateral injection of dopamine receptor agonists into the nucleus accumbens. The results demonstrate that there is no functional interaction between the cholinergic and dopaminergic substrates involved, although blockade of the dopamine receptors elicited behavioural deficits that competed with the turning elicited by carbachol. The contralateral turning elicited by carbachol injection into the nucleus accumbens requires an intact dopamine activity at the level of dopamine D1 and D2 receptors in the ipsilateral, but not contralateral, ventrolateral striatum.

Modifications of head turning and circling movement following sulpiride microinjections into nucleus accumbens in the rat

The aim of this study was to determine whether a relationship exists between nucleus accumbens D2 receptors, circling behavior, and its first stage, the head turning. Rats were unilaterally lesioned in the substantia nigra with 6-hydroxydopamine and afterward treated with d-amphetamine IP following bilateral intraaccumbens microinjections (1, 5, 10 micrograms/0.5 microliters) of sulpiride, a D2 receptor antagonist. Computer-assisted video analysis allowed the study of some parameters (number of turns, type of turn, head turning duration, degree and speed) characterizing rotatory activity. Sulpiride microinfusion resulted in a dose-dependent decrease of the number of turns and head rotation speed and in a dose-dependent increase of head-turning duration. Two turn types were observed in relation to the animal's position: a large head-to-tail position with a short-diameter turn type following sulpiride microinjection, and a close head-to-tail position in relation to a wide diameter turn type in the control condition (saline). The results show a relationship between head turning parameters, circling behavior, and D2 receptors in nucleus accumbens, which may be also involved in the regulation of some mechanisms related to sensory-motor integration in the rat.

Accumbens microinjection of LY 171555 and sulpiride: effects on circling behaviour, in the rat

In rats with unilateral 6-hydroxydopamine lesions of the substantia nigra (pars compacta) and amphetamine i.p. some parameters of the rotational activity, following intra-accumbens microinjection of D2 agonist (LY 171555) and antagonist (sulpiride), have been analyzed. An increase in the number of turns was observed with LY 171555, whereas sulpiride determined a decrease. The type of circling was also analyzed: D2 agonist induced a very close turn around the central axis of the animal and D2 antagonist a close turn in the centre of the cage. Data were compared with control condition, which exhibited a large turn around the walls of the cage. The results show that pharmacological manipulation of nucleus accumbens influences rotational behaviour with a specific role for D2 receptors.

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

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

Functional influence of the central noradrenergic system on the skin conductance activity in rats

Pharmacological studies on neuroleptics and amphetamine strongly suggest that some dysfunction of the central catecholamine system may play a key role in the pathogenesis of schizophrenia. Our previous studies have demonstrated that intraventricular administration of 6-hydroxydopamine, a selective neurotoxin of the catecholamine neuron, can reproduce schizophrenia-like abnormalities in the skin conductance activity. In the present experiments, effects of pharmacological modulation of the central noradrenergic activity were studied in rats. Stimulation of the central noradrenergic activity by yohimbine (0.6 mg/kg, i.m.) slowed down the habituation of the skin conductance response (SCR) and increase the spontaneous fluctuation of the skin conductance (SF), while inhibition of the activity by clonidine (0.06 mg/kg, i.m.) accelerated or obliterated the SCR and decreased the SF frequency. If the functional significance of the central noradrenergic system lies in vigilance control, the present results are consistent with classical theory in psychophysiology: the habituation rate of SCR and the frequency of SF are correlated well with each other and both indices reflect arousal level. The disorder of the system should produce not only these psychophysiological abnormalities but also psychological disturbances; i.e., overarousal and underarousal syndromes. Therefore, the dysfunction of the noradrenergic system might constitute an essential aspect of schizophrenic disorder.

Differential cholinergic and non-cholinergic actions of acetylcholinesterase in the substantia nigra revealed by fasciculin-induced inhibition

The effects of the peptide fasciculin (FAS), a potent inhibitor of acetylcholinesterase (AChE) have been examined, following unilateral microinfusion, on tissue levels of monoamines in the rat substantia nigra and concomitant circling behaviour. Although FAS inhibited 87% of total AChE, the levels of dopamine and its metabolites remained unchanged. Furthermore, the treatment induced modest contraversive rotation which was markedly enhanced in the presence of a systemic challenge with apomorphine. This behavioural effect of FAS was partially reversed by systemically administered atropine. Any possible interaction of FAS with nigral dopamine systems was further investigated by testing the peptide in animals that five days earlier had undergone a 6-hydroxydopamine (6-OHDA) lesion of the SN such that dopamine and AChE were significantly but not completely reduced. In a majority of these animals, FAS treatment caused a reversal of the lesion induced ipsiversive rotation, ie restored contraversive rotation. It is concluded that in the SN, FAS can have biochemical and behavioural actions independent of local dopamine systems and linked to cholinergic transmission. In addition, treatment with FAS in the substantia nigra also reveals the possible existence of at least two distinct pools of AChE with, respectively, non-cholinergic and cholinergic actions.

Ventral pallidal microinjections of receptor-selective opioid agonists produce differential effects on circling and locomotor activity in rats

Locomotor activity was investigated following microinjections of receptor-selective opioid agonists into the ventral pallidum (VP) of rats. In Expt. 1, male Long-Evans rats were treated with unilateral microinjections of the mu agonist [D-Ala2-MePhe4, Gly-ol5]-enkephalin (DAGO), the delta agonist [D-Pen2, D-Pen5]-enkephalin (DPDPE) or the kappa agonist U50,488H, and the rate and duration of circling behaviour were measured. DAGO (0.01, 0.1, 1.0 nmol) produced a dose-dependent increase in contralateral circling; pretreatment with 1.0 mg/kg naltrexone blocked the circling induced by the highest dose. The behavioral effect was largest when injections were targeted at the VP rather than structures dorsal to the VP. In contast to DAGO, intrapallidal DPDPE (0.01, 0.1, 1.0, 10.0 nmol) produced a slight increase in contralateral circling only at the highest dose and U50, 488H (0.01, 0.1, 1.0, 10.0 nmol) produced no effect. In Expt. 2, the effects of bilateral injections of DAGO, DPDPE and U50,488H were tested in photocell activity boxes. DAGO produced a dose-dependent increase in locomotor activity and this increase was decreased by 1.0 mg/kg naltrexone. A slight increase in activity was observed with the highest dose of DPDPE, and a slight decrease was observed with the highest dose of U50,488H. These findings confirm that opiate actions in the VP contribute to opiate-induced locomotion and suggest that mu and to some extent delta receptors are involved in this behavior.

Differential roles of the caudate nucleus and putamen in motor behavior of the cat as investigated by local injection of GABA antagonists

In order to reveal a functional difference between the two distinctly separate nuclei of the striatum, i.e. the caudate nucleus (Cd) and the putamen (Put), we studied the effects of local bicuculline (BIC) and picrotoxin (PTX) injection into these nuclei on the motor behavior in the cat. The extent of diffusion of the injected BIC could be approximated by determining the extent of spreading of the dye fast green FCF (FCF) mixed with BIC solution since the extent of diffusion of radioactive [3H]BIC mixed with BIC and FCF solution was almost the same as that of FCF.BIC and PTX are GABA antagonists and are assumed to activate efferent neurons of the Cd and Put by removing the action of GABA-ergic inhibitory synapses on them. A total of 28 BIC and 22 PTX injections was made in 20 adult cats, 22 aimed at the Cd and 28 at the Put. Injection of BIC or PTX to either the head or body of the Cd unilaterally induced locomotor hyperactivity without any postural asymmetry or circling tendency. When BIC or PTX was injected into the Put, dystonic movements (dystonia) towards the contralateral side appeared frequently in the neck and trunk. Even though the injected BIC or PTX often spread to the external segment of the globus pallidus, claustrum, or anterior sylvian gyrus, none of these areas was consistently associated with dystonia. These results demonstrate that the Cd and Put are differentially associated with locomotor and postural functions.

Skin conductance response after 6-hydroxydopamine lesion of central noradrenaline system in cats

Absence of skin conductance response (SCR) is a psychophysiological sign frequently observed among schizophrenic patients. This alteration of electrodermal activity can be reproduced in cats and rats by intraventricular administration of 6-hydroxydopamine (6-OHDA), a neurotoxin selectively destroying catecholamine neurons. The finding appears to be quite consistent with the catecholamine hypothesis of schizophrenia. To determine which catecholamine system--the dopamine (DA) or the noradrenaline (NA)--is responsible for the induction of this abnormality, the same dose of 6-OHDA was microinjected to either the ventral tegmental area (VTA, n = 3), through which most DA fibers ascend, or to the ascending noradrenergic bundle (ANB, n = 3), through which most NA fibers ascend. Four cats remained intact as a control for later brain catecholamine estimation. The skin conductance of all pretreatment intact cats (n = 10) showed not only spontaneous fluctuations but also SCRs to auditory stimuli (5 kHz, 100 dB, 1 sec) which habituated with repetition. In contrast, ANB-lesioned cats showed a complete abolition of auditory SCRs, few spontaneous fluctuations, and a low basal skin conductance level. These abnormalities were statistically significant. On the other hand, no change was found in the skin conductance activity of the VTA-lesioned cats. Catecholamine estimation after the experiment confirmed selective destruction of the appropriate system corresponding to each type of lesion. These findings are discussed in the context of the DA or NA theory of schizophrenia, and involvement of the NA system in the pathogenesis of this illness is suggested.

Relation between motor asymmetry and direction of rotational behaviour under amphetamine and apomorphine in rats with unilateral degeneration of the nigrostriatal dopamine system

The study examines whether in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra, the direction of amphetamine- and apomorphine-induced rotations is determined by a bias to step more frequently with one hindleg. Results show that there is a strong asymmetry in usage of hindlegs under apomorphine but a weak one under amphetamine. Moreover, under apomorphine, virtually all steps are backward. Under amphetamine, however, steps are directed both backward and forward, although backward steps are relatively more prevalent when striatal dopamine depletion is nearly total. The different styles of rotation reflect the activation of pure turning under apomorphine, and turning combined with forward progression under amphetamine. It is suggested that presence of forward progression during turning depends on the capacity to modulate striatal activation. Moreover, the different styles of rotation are inconsistent with the hypothesis that a bias in leg usage sets the direction of turning. Instead, it seems that unilateral striatal activation sets the directionality of turning, independent of any hindlimb motor asymmetries.

Anodal polarization in the substantia nigra increases rotational behavior in the rat

Rotational behavior was examined in rats after unilateral application of an anodal direct current (3 microA, 30 min) to the substantia nigra pars compacta (SNC). The current application increased contralateral rotation in two stages. One was during the period immediately after the current application, in which the increase in rotation declined within 30 min. The other period was long lasting, in which rotation increased 2 hr after the application and persisted for 24 hr or more. These results suggest that anodal direct currents induce transient and long-lasting activation of the SNC neurons, resulting in increases in rotational behavior.

A primate model of Huntington's disease: behavioral and anatomical studies of unilateral excitotoxic lesions of the caudate-putamen in the baboon

Unilateral caudate-putamen (CP) lesions induced by the glutamate receptor agonist ibotenic acid in baboons produced a neuropathological and behavioral model of Huntington's disease (HD) in the nonhuman primate. Neuropathological evaluation of the lesioned caudate-putamen revealed a neurodegenerative pattern resembling HD. The ibotenic acid-infused CP areas showed a neuronal loss in Nissl-stained sections and a marked astrocytic gliosis by immunohistochemical staining for glial-fibrillary-acidic protein. Acetylcholinesterase fiber staining was severely reduced in the lesioned CP, while afferent dopaminergic fibers, as shown by tyrosine hydroxylase staining, were relatively spared. There was a moderate reduction of met-enkephalin staining in the globus pallidus-pars lateralis ipsilateral to the ibotenic acid lesion, indicating a partial denervation of this structure following the lesion. In the behavioral studies a dyskinetic syndrome with features in common with HD was provoked in the lesioned animals following dopamine receptor agonist administration (1-2 mg/kg apomorphine). The symptoms included hyperkinesia, chorea, dystonia, postural asymmetries, head, and orofacial dyskinesia. The apomorphine test was highly reproducible and individual animals responded with a similar set and incidence of dyskinesia in successive tests. Since the behavioral observations following excitotoxic caudate-putamen damage parallel symptoms in HD patients given dopamine stimulatory drugs, a hypothesis is presented for the observed abnormal movements suggesting that the CP lesions reduce movement thresholds while the activation of dopaminoceptive regions induces dyskinesias.

Injections of 6-hydroxydopamine in the substantia nigra of the rat brain: morphological and biochemical effects

Rats with unilateral injections of 6-hydroxydopamine (6-OHDA) into the substantia nigra pars compacta were classified as active and inactive according to the intensity of their spontaneous and/or apomorphine-induced turning behavior (TB), and sacrificed at different survival times for morphological and biochemical analysis. In active rats, at any survival time, dopaminergic fluorescence in the nigrostriatal system as well as dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) content of the nucleus caudatus-putamen drastically decreased on the brain side ipsilateral to the injection. Dopaminergic fluorescence as well as DA and DOPAC content of the mesolimbic system ipsilateral to the injection also decreased. In inactive rats, at any survival time, 6-OHDA-induced lesions only partially involved both nigrostriatal and mesolimbic systems. Our results are indicative of a good correlation between the intensity of TB and the extent of 6-OHDA-induced lesions, as assessed by morphological and biochemical analysis.

Is there a right hemi-hyper-dopaminergic psychosis?

This selective review argues that a small subgroup among the patients meeting DSM-III-R criteria for schizophrenia appears to have an underlying right striatal hyper-dopaminergia. The subgroup is distinguished by a group of objective signs including: (1) asymmetric, usually right-sided, neuroleptic induced parkinsonian side effects; (2) asymmetric, usually left-sided, tardive dyskinesia; (3) a subclinical tendency to turn toward the left; (4) a subclinical right hemi-space sensory neglect; and (5) dopamine receptor densities greater in the right striatum than in the left.

MIF-1 attenuates apomorphine stereotypies in adult rats after neonatal 6-hydroxydopamine

Since prolyl-leucyl-glycinamide (MIF-1) modifies the behavior of adult rats after treatment with neuroleptics, we examined whether MIF-1 would also modify adult behavior after treatment of neonatal rats with 6-hydroxydopamine (6-OHDA). Rats received 6-OHDA (100 micrograms i.c.v.) or diluent at 3 days after birth and either MIF-1 (2.0 mg/kg per day s.c. x 10 days) or diluent beginning at 28 or 29 days after birth. At 5 weeks, a low dose (0.1 mg/kg s.c.) of apomorphine increased the distance traveled, time in ambulation, number of stereotypic movements, and number of movements per time in stereotypy, but decreased the time in stereotypy in the 6-OHDA group. MIF-1 (x 7 or 8 days) showed a tendency to attenuate the increased number of movements and significantly (P less than 0.05) reduced all of the other effects of neonatal 6-OHDA. Behavior induced by higher doses of apomorphine in the 6-OHDA group (reduced licking and head nodding; increased paw treading, taffy pulling and self-biting) were not attenuated by MIF-1. At 38 or 39 days, total in vitro binding of [3H]SCH-23390 and [3H]spiroperidol to striatal homogenates was not altered in any of the groups. The findings demonstrate that specific early developmental alterations in apomorphine-induced behaviors can be modified by treatment of adult rats with MIF-1, even in the absence of overt changes in the binding of striatal dopamine D-1 and D-2 receptors.