The relationship between hindlimb disturbances, forelimb disturbances and catalepsy after increasing doses of muscimol injected into the striatal-pallidal complex

Differential effect of NR2A and NR2B subunit selective NMDA receptor antagonists on striato-pallidal neurons: relationship to motor response in the 6-hydroxydopamine model of parkinsonism

We previously demonstrated that NMDA receptors containing the NR2A or NR2B subunits differentially regulate striatal output pathways. We now investigate whether such a differential control is altered under parkinsonian conditions and whether subunit selective antagonists have different abilities to attenuate parkinsonian-like motor deficits. Three microdialysis probes were simultaneously implanted in the dopamine-depleted striatum, globus pallidus and substantia nigra reticulata of 6-hydroxydopamine hemilesioned rats. The NR2A antagonist NVP-AAM077 perfused in the striatum reduced pallidal GABA, but not glutamate, levels whereas the NR2B antagonist Ro 25-6981 was ineffective. Neither antagonist affected striatal or nigral amino acid levels. To investigate whether these neurochemical responses were predictive of different antiparkinsonian activities, antagonists were administered systemically and motor activity evaluated in different motor tasks. Neither antagonist attenuated akinesia/bradykinesia in the bar and drag test. However, NVP-AAM077 dually modulated rotarod performance (low doses being facilitatory and higher ones inhibitory) while Ro 25-6981 monotonically improved it. Microdialysis revealed that motor facilitating doses reduced pallidal GABA levels while motor inhibiting doses increased them. We conclude that, under parkinsonian conditions, the striato-pallidal pathway is driven by striatal NR2A subunits. Motor improvement induced by NVP-AAM077 and Ro 25-6981 is accomplished by blockade of striatal NR2A and extrastriatal NR2B subunits, respectively.

Transient striatal delivery of GDNF via encapsulated cells leads to sustained behavioral improvement in a bilateral model of Parkinson disease

Numerous studies have shown the neuroprotective and regenerative benefits of glial cell line-derived neurotrophic factor (GDNF) in animal models of PD. Brain delivery of GDNF can, however, be associated with limiting side-effects in both primates and PD patients, rendering the duration of delivery a critical factor. In the present study, the effects of transient vs. sustained GDNF delivery by encapsulated cells were evaluated in a bilateral animal model, closely mimicking advanced PD. One week following bilateral striatal 6-hydroxydopamine injections in rats, capsules loaded with human fibroblasts genetically engineered to release GDNF were bilaterally implanted in the striatum. GDNF delivery resulted in a significant improvement of movement initiation and swimming performance in the lesioned animals, associated with striatal reinnervation of dopaminergic fibers. To test the sustainability of the behavioral improvement, GDNF-secreting capsules were withdrawn in a subgroup of animals, 7 weeks post-implantation. Strikingly, both the behavioral and morphological improvements were maintained until the sacrifice of the animals 6 weeks post-GDNF withdrawal. The sustained cellular and behavioral benefits after GDNF washout suggest the need for temporary delivery of the trophic factor in PD. Retrievable encapsulated cells represent an attractive delivery tool to achieve this purpose.

Convergent evidence from microdialysis and presynaptic immunolabeling for the regulation of gamma-aminobutyric acid release in the globus pallidus following acute clozapine or haloperidol administration in rats

Antipsychotic drugs (APDs) have been primarily characterized for their effects on dopaminergic terminal regions in the brain, especially within the corpus striatum. Efferent GABA pathways are the primary outflow of striatal processing via their projections to the substantia nigra and the globus pallidus (GP). In the current study, we analyzed changes in pallidal GABA function following acute APD administration by means of in vivo microdialysis, followed by immunolabeling of presynaptic GABA terminal density in the contralateral hemisphere of the same animals. Acute administration of the atypical APD, clozapine (10 or 30 mg/kg, s.c.), produced a dose-dependent decrease in extracellular GABA. A corresponding dose-dependent increase in the density of presynaptic terminal GABA immunolabeling in the GP was found. In contrast, the typical APD, haloperidol (1 or 3 mg/kg, s.c.), had no significant effects on either measure, although a non-significant increase in extracellular GABA and decrease in the density of GABA terminal immunolabeling was noted. Paw retraction tests conducted during the time of microdialysis showed that haloperidol produced a typical pattern of highly pronounced motor impairment, while clozapine showed an atypical profile of minimal catalepsy. These complementary results obtained from in vivo neurochemistry and presynaptic neurotransmitter labeling suggest that systemic clozapine suppresses neuronal GABA release within the GP. This decrease in released pallidal GABA may play a role in the low motor side-effect liability of atypical APDs.

Sensorimotor impairments in rats with cerebral infarction, induced by unilateral occlusion of the left middle cerebral artery: strain differences and effects of the occlusion site

Enormous differences exist between rat strains with respect to the infarct volume induced by unilateral middle cerebral artery (MCA) occlusion. We performed three experiments to address the following questions. Firstly, whether the pattern of MCA-occlusion (MCA-O) induced sensorimotor impairments in rats are strain dependent; secondly, whether proximal (i.e., close to its origin) and distal occlusions (above the lenticulostriate branch) of the MCA affect infarct volume and the behavioral impairments to a different extent; and thirdly, whether there is a relationship between the infarct volume and behavioral deficits. We found that the pattern of sensorimotor malfunctions induced by proximal unilateral MCA-O were highly strain dependent. Of the eight strains tested, Winkelmann-Wistar rats, Spontaneously Hypertensive Stroke-Prone rats, and Wistar-Kyoto rats were most severely affected. By contrast, Brown-Norway rats showed only mild behavioral deficits after the MCA-O. The second experiment confirmed that proximal occlusions induced slightly more behavioral malfunctions than distal occlusions did. Histological evaluation of the brain damage caused by proximal and distal MCA-O, confirmed that distal MCA-O damaged nearly exclusively cortical areas, and spared the caudate/putamen. An exploratory analysis of the relationship between infarct volume and behavioral deficits did not indicate that the severity of sensorimotor malfunctions can be predicted from the size of the infarct.

Sensorimotor impairments in Wistar Kyoto rats with cerebral infarction, induced by unilateral occlusion of the middle cerebral artery: recovery of function

Wistar Kyoto (WKY) rats with cerebral infarction induced by permanent unilateral occlusion of the middle cerebral artery (MCA) and sham-operated rats were tested in a series of simple behavioral test 2, 16 and 37 days after surgery. In addition, the motility of the animals was measured over a period of 62 h, after the third test series. A subset of the tests appeared to be suitable to assess the effects of cerebral infarction, namely, grasping reflex of contralateral hindpaw, circling behavior, forelimb flexion, hindlimb flexion, and latency to fall off a square bridge. Except for the impaired grasping reflex of the contralateral hindpaw, there was spontaneous complete recovery of function by the third test session, 37 days after surgery. Some of the other tests might not have been sensitive enough to detect the effects of the unilateral MCA-occlusion (MCA-O) on behavior. Moreover, the WKY rats were very inactive in some of the tests, so that reliable scoring of the effects was not always possible. A rat strain other than the WKY strain might be more suitable to study the behavioral consequences of MCA-O.

Treatment of schizophrenia: a clinical and preclinical evaluation of neuroleptic drugs

Forty years after the first clinical report on the effectiveness of chlorpromazine in psychiatric patients, neuroleptic drugs are still the most widely used drugs in the treatment of schizophrenia. Indeed, there are no other drugs which have proven to be as effective in the treatment of this severe psychiatric disorder. Yet, there are still many unresolved problems relating to neuroleptic drugs. The present review gives a comprehensive overview of our knowledge (and our lack of knowledge) with respect to the clinical and preclinical effects of neuroleptic drugs and tries to integrate this knowledge in order to identify the neuronal mechanisms underlying the therapeutic and side effects of neuroleptic drugs.

Behavioral effects of modulators of ATP-sensitive K+ channels in the rat dorsal pallidum

The effects of the potent ATP-sensitive K+ channel blocker glipizide were measured on the locomotor activity of rats after bilateral intracerebral administration into the dorsal pallidum. Glipizide (10 pmol) was found to reduce spontaneous locomotor activity measured during the night cycle of the rats, whereas the ATP-sensitive K+ channel activator (-)-cromakalim (5 fmol) enhanced spontaneous locomotor activity. Glipizide (0.5, 2.5 and 10 pmol) was also found to depress noticeably d-amphetamine-induced locomotor activity (1 mg/kg s.c.). These results are in agreement with the idea that ATP-dependent potassium channels within the dorsal pallidum are involved in controlling motor activity in the rat.

Search after neurobiological profile of individual-specific features of Wistar rats

The first part of this study demonstrates that the bimodal shape of variation in "fleeing" and "nonfleeing" or "freezing" rats of an outbred strain of Wistar rats forms part of an overall biomodal variation in behavioural responses to injections of agents, which selectively alter, or reflect, the noradrenergic or dopaminergic activity in the ventral striatum, and dopaminergic activity in the dorsal striatum, the GABA-ergic activity in the substantia nigra, pars reticulata, and the GABA-ergic activity in the deeper layers of the superior colliculus. It is concluded that the "fleeing" and "nonfleeing" rats, each of them marked by their own trans-situational consistency in pharmacological and behavioural responses, represent the two fundamentally different types of individuals which normally exist in unselected populations of rodents. The second part of this study demonstrates that the pharmacogenetic selection of apomorphine-susceptible (APO-SUS) and apomorphine-unsusceptible (APO-UNSUS) rats, i.e., one individual-specific feature of the overall bimodal variation for pharmacological responses in our outbred strain of rats, is a valid tool to disperse the above-mentioned individual-specific features as far as possible. First, these lines allowed us to prove that the overall bimodal shape of variation in pharmacological and behavioral responses of individual outbred rats is in part genetically determined. Second, these lines allowed us to prove that a bimodal variation in neurochemical features of the circuitry, in which the ventral striatum is embedded, underlies the overall bimodal variation in pharmacological and behavioural responses. Third, these lines allowed us to demonstrate that a fundamental difference in organizing behaviour with the help of external and internal information has to be considered as a common factor giving rise to the individual differentiation found in the present study. Given the notion that this individual differentiation appears to be valid across lines, substrains and strains of rats, the present study lays the foundation for understanding at least a part of the physiological basis underlying differences between the two fundamentally different types of individuals existing in normal populations of rodents.

Evidence that apomorphine and (+)-amphetamine produce different types of circling in rats

Apomorphine and (+)-amphetamine are known to produce circling in naive rats. Frame by frame analysis of videotape recordings of the behaviour of Wistar rats treated with a subcutaneous injection of apomorphine (1.1 mg/kg; n = 8) or (+)-amphetamine (0.5 and 1.0 mg/kg; n = 8 and n = 8) was used to study this behaviour in more detail. In line with previously reported studies, apomorphine was found to change the functioning of hindlimb stepping. In contrast, (+)-amphetamine was found to change the functioning of forelimb stepping. These data imply that apomorphine and (+)-amphetamine produce their drug-specific circling via different substrates within the brain.

Dorsal pallidum as a functional motor output of the corpus striatum

A major function of the dopamine in the striatum is to control the activity of its efferent systems which contain primarily GABAergic neurons. Direct intracerebral injections of haloperidol into the corpus striatum impaired the performance of rats trained to depress a lever in a sensitive reaction time task. Rats were trained to depress a lever until the presentation of a visual conditioned stimulus and then to release the lever within a time limit of 500 ms to obtain a food reward. The increase in reaction time produced by dopamine blockade of the corpus striatum was mimicked by injection of a GABA agonist muscimol in nanogram quantities into the region of the dorsal pallidum, but not into the substantia nigra reticulata. Injections of a GABA agonist into the substantia nigra impaired performance by increasing the number of anticipatory responses (increased number of lever releases before the conditioned stimulus). These results suggest that the dorsal pallidum may play an important role in the response initiation associated with activation of the corpus striatum, and that the dorsal pallidum may form a significant part of parallel striatal outputs that have different functional significance.

The Paw test: an animal model for neuroleptic drugs which fulfils the criteria for pharmacological isomorphism

Recently we have developed an animal model which could discriminate between classical and atypical neuroleptic drugs: the PAW TEST. This test measures the ability of rats to spontaneously withdraw its force- and hindlimbs. It was found that the ability of drugs to affect the rat's forelimb retraction time was associated with the liability of the drug to induce so-called extra-pyramidal side-effects in man. Likewise the ability of drugs to affect the rat's hindlimb retraction time was associated with the antipsychotic efficacy of the drug. These data open the perspective that the forelimb retraction time (FRT) is an animal analogue of parkinsonian side-effects, and that the hindlimb retraction time (HRT) is an animal analogue of antipsychotic effects In the present series of experiments we further evaluated the validity of these notions by applying the criteria of "pharmacological isomorphism" as proposed by Matthysse (1). Thus HRT had to fulfil the criteria of pharmacological isomorphism for the therapeutic effects of neuroleptics, whereas FRT had to fulfil these criteria for the parkinsonian side-effects. The results of the present study show that both FRT and HRT met these criteria. Thus both classical and atypical neuroleptics were effective in prolonging HRT, whereas only the classical neuroleptics prolonged FRT (criterion 1); the nonneuroleptic phenothiazine promethazine (as well as the narcotic morphine, the muscle relaxant diazepam and the antidepressant desipramine) were ineffective in this respect (criterion 2); the acetylcholinergic antagonist scopolamine blocked the FRT, but not the HRT (criterion 3); chronic neuroleptic treatment reduced the FRT, but not the HRT (criterion 4). In conclusion the paw test, an animal model for testing antipsychotic drugs, was found to fulfil the criteria for "pharmacological isomorphism". Although the exact mechanism underlying the paw test is as yet unknown, the present data improve its validity as an animal model.