Striatal and nucleus accumbens D1/D2 dopamine receptors in neuroleptic catalepsy

Paradoxical kinesia may no longer be a paradox waiting for 100 years to be unraveled

Parkinson's disease (PD) is a progressive neurodegenerative disorder mainly characterized by bradykinesia and akinesia. Interestingly, these motor disabilities can depend on the patient emotional state. Disabled PD patients remain able to produce normal motor responses in the context of urgent or externally driven situations or even when exposed to appetitive cues such as music. To describe this phenomenon Souques coined the term "paradoxical kinesia" a century ago. Since then, the mechanisms underlying paradoxical kinesia are still unknown due to a paucity of valid animal models that replicate this phenomenon. To overcome this limitation, we established two animal models of paradoxical kinesia. Using these models, we investigated the neural mechanisms of paradoxical kinesia, with the results pointing to the inferior colliculus (IC) as a key structure. Intracollicular electrical deep brain stimulation, glutamatergic and GABAergic mechanisms may be involved in the elaboration of paradoxical kinesia. Since paradoxical kinesia might work by activation of some alternative pathway bypassing basal ganglia, we suggest the IC as a candidate to be part of this pathway.

The Arousal-motor Hypothesis of Dopamine Function: Evidence that Dopamine Facilitates Reward Seeking in Part by Maintaining Arousal

Dopamine facilitates approach to reward via its actions on dopamine receptors in the nucleus accumbens. For example, blocking either D1 or D2 dopamine receptors in the accumbens reduces the proportion of reward-predictive cues to which rats respond with cued approach. Recent evidence indicates that accumbens dopamine also promotes wakefulness and arousal, but the relationship between dopamine's roles in arousal and reward seeking remains unexplored. Here, we show that the ability of systemic or intra-accumbens injections of the D1 antagonist SCH23390 to reduce cued approach to reward depends on the animal's state of arousal. Handling the animal, a manipulation known to increase arousal, was sufficient to reverse the behavioral effects of the antagonist. In addition, SCH23390 reduced spontaneous locomotion and increased time spent in sleep postures, both consistent with reduced arousal, but also increased time spent immobile in postures inconsistent with sleep. In contrast, the ability of the D2 antagonist haloperidol to reduce cued approach was not reversible by handling. Haloperidol reduced spontaneous locomotion but did not increase sleep postures, instead increasing immobility in non-sleep postures. We place these results in the context of the extensive literature on dopamine's contributions to behavior, and propose the arousal-motor hypothesis. This novel synthesis, which proposes that two main functions of dopamine are to promote arousal and facilitate motor behavior, accounts both for our findings and many previous behavioral observations that have led to disparate and conflicting conclusions.

In vivo Evidence for Brain Region-Specific Molecular Interactions Between Cannabinoid and Orexin Receptors

The endocannabinoid and orexin neuromodulatory systems serve key roles in many of the same biological functions such as sleep, appetite, pain processing, and emotional behaviors related to reward. The type 1 cannabinoid receptor (CB1R) and both subtypes of the orexin receptor, orexin receptor type 1 (OX1R) and orexin receptor type 2 (OX2R) are not only expressed in the same brain regions modulating these functions, but physically interact as heterodimers in recombinant and neuronal cell cultures. In the current study, male and female C57BL/6 mice were co-treated with the cannabinoid receptor agonist CP55,940 and either the OX2R antagonist TCS-OX2-29 or the dual orexin receptor antagonist (DORA) TCS-1102. Mice were then evaluated for catalepsy, body temperature, thermal anti-nociception, and locomotion, after which their brains were collected for receptor colocalization analysis. Combined treatment with the DORA TCS-1102 and CP55,940 potentiated catalepsy more than CP55,940 alone, but this effect was not observed for changes in body temperature, nociception, locomotion, or via selective OX2R antagonism. Co-treatment with CP55,940 and TCS-1102 also led to increased CB1R-OX1R colocalization in the ventral striatum. This was not seen following co-treatment with TCS-OX2-29, nor in CB1R-OX2R colocalization. The magnitude of effects following co-treatment with CP55,940 and either the DORA or OX2R-selective antagonist was greater in males than females. These data show that CB1R-OX1R colocalization in the ventral striatum underlies cataleptic additivity between CP55,940 and the DORA TCS-1102. Moreover, cannabinoid-orexin receptor interactions are sex-specific with regards to brain region and functionality. Physical or molecular interactions between these two systems may provide valuable insight into drug-drug interactions between cannabinoid and orexin drugs for the treatment of insomnia, pain, and other disorders.

Zona incerta as a therapeutic target in Parkinson's disease

The zona incerta has recently become an important target for deep-brain stimulation (DBS) in Parkinson's disease (PD). The present review summarizes clinical, animal and anatomical data which have indicated an important role of this structure in PD, and discusses potential mechanisms involved in therapeutic effects of DBS. Animal studies have suggested initially some role of neurons as well as GABAergic and glutamatergic receptors of the zona incerta in locomotion and generation of PD signs. Anatomical data have indicated that thanks to its multiple interconnections with the basal ganglia, thalamus, cerebral cortex, brainstem, spinal cord and cerebellum, the zona incerta is an important link in a neuronal chain transmitting impulses involved in PD pathology. Finally, clinical studies have shown that DBS of this structure alleviates parkinsonian bradykinesia, muscle rigidity and tremor. DBS of caudal zona incerta seemed to be the most effective therapeutic intervention, especially with regard to reduction of PD tremor as well as other forms of tremor.

Dopamine D1 and muscarinic acetylcholine receptors in dorsal striatum are required for high speed running

Dopamine (DA) signaling in the basal ganglia plays important roles in motor control. Motor deficiencies were previously reported in dopamine receptor D1 (D1R) and D2 (D2R) knockout mice. While these results indicate the involvement of DA receptors in motor execution, the null knockout (KO) mouse lacks the specificity necessary to determine when and where in the brain D1R and D2R function in motor execution. To address these questions, we restricted the loss of function temporally and spatially by using D1R conditional knockdown (cKD) mice and mice injected with antagonists against DA receptors directly into the dorsal striatum. In addition, we address the DA and acetylcholine (ACh) balance hypothesis by using antagonists against ACh receptors. We tested the motor ability of the mice with a newly devised task named the accelerating step-wheel. In this task, the maximum running speed was measured in a situation where the wheel rotation speed was gradually accelerated in one trial. We found significant decreases in the maximum running speed of D1R cKD mice and the mice injected with the antagonist against D1R or muscarinic ACh receptor. These results indicated that D1R and muscarinic ACh receptor in the dorsal striatum play pivotal roles in the execution of walking/running.

Cyclosomatostatin- and haloperidol-induced catalepsy in Wistar rats: Differential responsiveness to sleep deprivation

Total sleep deprivation (SD) has been found to mitigate motor dysfunctions in Parkinson's disease. Apparently, the similar sensitivity of an animal model for parkinsonism would support the model's validity. Recently, we described catalepsy induced in Wistar rats by somatostatin antagonist, cyclosomatostatin (cSST); this model simulates such a disease-associated abnormality as a fall in brain somatostatin levels. To evaluate the similarity between the cSST model and Parkinson's disease, we assessed here the responsiveness of cSST-induced catalepsy to 1-h and 3-h SD. In parallel, the influence of SD on catalepsy induced by a dopamine receptor antagonist, haloperidol, was examined. It was found that the short-term SD failed to influence cataleptic responses of both types (sleep deprived rats and undisturbed ones displayed a similar duration of immobility, p > 0.05). By contrast, 3-h SD suppressed (p < 0.01) cSST-induced catalepsy, however, enhanced (p < 0.01) cataleptic response to haloperidol. Thus, the anti-cataleptic effect of SD appears to be cSST-specific. These findings support the validity of the cSST-induced catalepsy in Wistar rats as a model for parkinsonian motor dysfunctions.

Antiallergic and antihistaminic actions of Ceasalpinia bonducella seeds: Possible role in treatment of asthma

ETHNOPHARMACOLOGICAL RELEVANCE

Seed kernel of the plant Ceasalpinia bonducella Linn (Caesalpiniacaeae) are used for the treatment of asthma in folk medicine and ancient books.

AIM OF STUDY

To assess the pharmacological efficacy of the plant in asthma and to confine and describe the synthetic constituents from the seeds that are in charge of the action.

MATERIAL AND METHODS

The viability of petroleum ether, ethanol extract and ethyl acetate fraction from ethanol extract of C. bonducella seeds were screened for the treatment of asthma by various methods viz. effect of test drug on clonidine and haloperidol induced catalepsy, milk-induced leukocytosis and eosinophilia, mast cell stabilizing activity in mice and studies on smooth muscle preparation of guinea pig ileum (in-vitro). Column chromatography of active extract was done to pinpoint the active compound followed by structure elucidation by FTIR, GCMS and NMR spectroscopic methods.

RESULTS

Ethyl acetate fraction from ethanol extract of C. bonducella seeds exhibited antihistaminic activity at the dose of 50 and 100 mg/kg, inhibited clonidine-induced catalepsy but not haloperidol-induced catalepsy. Ethyl acetate fraction from ethanol extract significantly inhibited increased leukocyte and eosinophil count due to milk allergen and showed maximum protection against mast cell degranulation by clonidine. The results of guinea pig ileum indicated that the compound 2 methyl, 1 hexadecanol isolated from ethyl acetate fraction of ethanol extract relaxed significantly the ileum muscle strips pre-contracted by which suggests the involvement of β₂-agonists on the relaxation of the tissue. All the results are dose dependent. Active ethyl acetate fraction from ethanol extract showed presence of anti-asthmatic compound, 2-methyl, 1-hexadecanol.

CONCLUSION

The ethyl acetate fraction from ethanol extract of seeds of the plant C. bonducella can inhibit parameters linked to asthma disease.

Short- and long-term effects of risperidone on catalepsy sensitisation and acquisition of conditioned avoidance response: Adolescent vs adult rats

The effects of antipsychotic drugs (APDs) on the adolescent brain are poorly understood despite a dramatic increase in prescription of these drugs in adolescents over the past twenty years. Neuronal systems continue to be remodeled during adolescence. Therefore, when given in adolescence, antipsychotic drugs (APDs) have the potential to affect this remodeling. In this study we investigated the effects of chronic 22-day risperidone treatment (1.3mg/kg/day) in both adolescent and adult rats. We examined short- and long-term changes in behaviour (catalepsy, locomotion and conditioned avoidance response (CAR)), and dopaminergic and serotonergic neurochemistry in the striatum and the nucleus accumbens. Here, we report that, both during chronic treatment and after a lengthy drug-free interval, risperidone induced a sensitised cataleptic response regardless of the age of exposure. Selectively in adolescents, risperidone-induced catalepsy was inversely correlated with striatal dopamine turnover immediately after chronic treatment. After a drug-free interval, a significant proportion of rats with prior adolescent risperidone treatment also failed to acquire CAR to a defined criterion. Our data provide evidence that the same chronic risperidone treatment regimen can induce contrasting short- and long-term neural outcomes in the adolescent and adult brains.

CB1 cannabinoid receptor-mediated anandamide signaling mechanisms of the inferior colliculus modulate the haloperidol-induced catalepsy

The inferior colliculus (IC), a midbrain structure that processes acoustic information of aversive nature, is distinguished from other auditory nuclei in the brainstem by its connections with structures of the motor system. Previous evidence relating the IC to motor behavior shows that glutamatergic and GABAergic mechanisms in the IC exert influence on systemic haloperidol-induced catalepsy. There is substantial evidence supporting a role played by the endocannabinoid system as a modulator of the glutamatergic neurotransmission, as well as the dopaminergic activity in the basal nuclei and therefore it may be considered as a potential pharmacological target for the treatment of movement disorders. The present study evaluated if the endocannabinoid system in the IC plays a role in the elaboration of systemic haloperidol-induced catalepsy. Male Wistar rats received intracollicular microinjection of either the endogenous cannabinoid anandamide (AEA) at different concentrations (5, 50 or 100pmol/0.2μl), the CB₁ cannabinoid receptor antagonist AM251 at 50, 100 or 200pmol/0.2μl or vehicle, followed by intraperitoneal (IP) administration of either haloperidol at 0.5 or 1mg/kg or physiological saline. Systemic injection of haloperidol at both doses (0.5 or 1mg/kg, IP) produced a cataleptic state, compared to vehicle/physiological saline-treated group, lasting 30 and 50min after systemic administration of the dopaminergic receptors non-selective antagonist. The midbrain microinjection of AEA at 50pmol/0.2μl increased the latency for stepping down from the horizontal bar after systemic administration of haloperidol. Moreover, the intracollicular administration of AEA at 50pmol/0.2μl was able to increase the duration of catalepsy as compared to AEA at 100pmol/0.2-μl-treated group. Intracollicular pretreatment with AM251 at the intermediate concentration (100pmol/0.2μl) was able to decrease the duration of catalepsy after systemic administration of haloperidol. However, neither the intracollicular microinjection of AM251 at the lowest (50pmol/0.2μl) nor at the highest (200pmol/0.2μl) concentration was able to block the systemic haloperidol-induced catalepsy. Furthermore, the intracollicular administration of AM251 at 100pmol/0.2μl was able to decrease the duration of catalepsy as compared to AM251 at 50pmol/0.2μl- and AM251 at 200pmol/0.2-μl-treated group. The latency for stepping down from the horizontal bar - induced by haloperidol administration - was decreased when microinjection of AEA at 50pmol/0.2μl was preceded with blockade of CB1 receptor with AM251 (100pmol/0.2μl). Our results strengthen the involvement of CB1-signaled endocannabinoid mechanisms of the IC in the neuromodulation of catalepsy induced by systemic administration of the dopaminergic receptors non-selective antagonist haloperidol.

The potency and efficacy of anticholinergics to inhibit haloperidol-induced catalepsy in rats correlates with their rank order of affinities for the muscarinic receptor subtypes

Extrapyramidal syndromes (EPS) caused by antipsychotic therapy are currently treated with anticholinergics that lack selectivity for the five muscarinic receptor subtypes. Since these receptors are heterogeneously expressed among the different classes of striatal neurons and their afferents, it can be expected that their simultaneous blockade will cause distinct, sometimes opposed, effects within the striatal circuitry. In order to test the hypothesis that the differential blockade of the muscarinic receptor subtypes would influence their potency and efficacy to prevent EPS, here we tested four anticholinergics with varying order of affinities for the muscarinic receptor subtypes, and compared their dose-response curves to inhibit haloperidol-induced catalepsy in male rats. Drugs were applied into the lateral ventricle 15 min before haloperidol (2 mg/kg, s.c.). Catalepsy was measured in the bar test at 15 min intervals during 5 h. The preferential M1/M4 antagonist pirenzepine (3, 10, 30, 100, and 300 nmol) caused a dose-dependent inhibition of catalepsy intensity: ED50 = 5.6 nmol [95% CI, 3.9-8.1], and latency: ED50 = 5.6 nmol [95% CI, 3.7-8.6]. Pirenzepine had the steepest dose-response curve, producing maximal inhibition (84 ± 5%) at the dose of 10 nmol, while its effect tended to reverse at higher doses (62 ± 11%). The purported M1/M3 antagonist 4-DAMP (30, 100, and 300 nmol) also caused a dose-dependent inhibition of catalepsy intensity: ED50 = 29.5 nmol [95% CI, 7.0 to 123.0], and latency: ED50 = 28.5 nmol [95% CI, 2.2 to 362.0]. However, the curve for 4-DAMP had a less pronounced slope, reaching its maximal effect (63 ± 14%) at the dose of 300 nmol. The M2/M4 antagonist AF-DX 116 (10, 30, and 300 nmol) only caused a partial inhibition of catalepsy (30 ± 11%) at the dose of 30 nmol, but this changed to a non-significant increment (15 ± 10%) at the dose of 100 nmol. The alleged M4 antagonist tropicamide (30, 100, 300, and 600 nmol) produced a partial inhibition of catalepsy (36 ± 12%) at the dose of 300 nmol, but lacked effect at higher or lower doses. Concurrent treatment with pirenzepine (10 nmol) and tropicamide (300 nmol) produced an effect similar to that of tropicamide alone. The greater potency and efficacy of pirenzepine for catalepsy inhibition could be due to its higher affinity for M1 receptors and, to a lesser extent, for M4 receptors. It is suggested that selective M1 antagonists would be more effective than M2, M3 or M4 antagonists to prevent EPS caused by antipsychotic drugs.

Haloperidol conditioned catalepsy in rats: a possible role for D1-like receptors

Decreases in brain dopamine (DA) lead to catalepsy, quantified by the time a rat remains with its forepaws resting on a suspended horizontal bar. Low doses of the DA D2 receptor-preferring antagonist haloperidol repeatedly injected in a particular environment lead to gradual day-to-day increases in catalepsy (catalepsy sensitization) and subsequent testing following an injection of saline reveal conditioned catalepsy. We tested the hypothesis that D1-like and D2 receptors play different roles in catalepsy sensitization and in acquisition and expression of conditioned catalepsy. Rats were repeatedly treated with the DA D1-like receptor antagonist SCH 23990 (0.05, 0.1 and 0.25 mg/kg i.p.), the D2 receptor-preferring antagonist haloperidol (0.1, 0.25 and 0.5 mg/kg i.p.) or a combination of the two drugs and tested for catalepsy each day in the same environment. Following 10 drug treatment days, rats were injected with saline and tested for conditioned catalepsy in the previously drug-paired environment. Haloperidol did not elicit cataleptic responses in the initial session; however, rats developed sensitization with repeated testing. Significant catalepsy sensitization was not observed in rats repeatedly tested with SCH 23390. When rats were injected and tested with saline following haloperidol sensitization they exhibited conditioned catalepsy in the test environment; conditioned catalepsy was not seen following SCH 23390. Rats treated with 0.05 mg/kg SCH 23390+0.25 mg/kg haloperidol showed catalepsy sensitization but failed to show conditioned catalepsy. Conversely, SCH 23390 (0.05 mg/kg) given on the test day after sensitization to haloperidol (0.25 mg/kg) failed to block conditioned catalepsy. Repeated antagonism of D2 receptors leads to catalepsy sensitization with repeated testing in a specific environment. Conditioned catalepsy requires intact D1-like receptor function during sensitization sessions but not during test sessions. In conclusion, repeated antagonism of D2, but not D1-like receptors leads to catalepsy sensitization with repeated testing in a specific environment. Conditioned catalepsy requires functional D1-like receptors during sensitization sessions but not during test sessions.

Antihistaminic and antiallergic actions of extracts of Solanum nigrum berries: possible role in the treatment of asthma

ETHNOPHARMACOLOGICAL RELEVANCE

Berries of the plant Solanum nigrum Linn (Solanaceae) are used for the treatment of asthma in folk medicine and ancient books.

AIM OF STUDY

To evaluate potential of the plant berries in the treatment of asthma.

MATERIALS AND METHODS

Petroleum ether, ethanol and aqueous extracts of S. nigrum berries (50, 100 and 200mg/kg, i.p.) were screened for the treatment of asthma by the various methods viz. effect on clonidine and haloperidol induced catalepsy, milk-induced leucocytosis and eosinophilia, mast cell stabilizing activity in mice and studies on smooth muscle preparation of guinea pig ileum (in vitro). Active petroleum ether extract was standardized by HPTLC.

RESULTS

The petroleum ether extract of S. nigrum berries inhibited clonidine-induced catalepsy significantly but not haloperidol-induced catalepsy. Petroleum ether extract significantly inhibited increased leukocyte and eosinophil count due to milk allergen and showed maximum protection against mast cell degranulation by clonidine. Petroleum ether extract resisted contraction induced by histamine better than other extracts. All the results are dose dependant. Active petroleum ether extract showed presence of antiasthmatic compound, β-sitosterol.

CONCLUSION

The petroleum ether extract of S. nigrum berries can inhibits parameters linked to the asthma disease.

Antihistaminic effect of Bauhinia racemosa leaves

Bauhinia racemosa Lam. (Caesalpiniaceae) leaves have been used in the treatment of asthma traditionally and we therefore undertook this study to scientifically validate its benefit in asthma using suitable animal models. Antihistaminic principles are known to be useful in the treatment of asthma; hence, in the present work, the antihistaminic activity of an ethanol extract of B. racemosa (at a dose of 50 mg/kg, i.p.) was assessed using clonidine-induced catalepsy and haloperidol-induced catalepsy in Swiss albino mice. The results showed that the ethanol extract inhibits clonidine-induced catalepsy but there is no effect on haloperidol-induced catalepsy. This suggests that the inhibition is through an antihistaminic action and that there is no role of dopamine. Hence, we concluded that the ethanol extract has significant antihistaminic activity. The polar constituents in the ethanol extract of leaves of B. racemosa may be responsible for the antihistaminic activity and B. racemosa may therefore have a role in the treatment of asthma.

Design, synthesis and anti-Parkinsonian evaluation of 3-alkyl/aryl-8-(furan-2-yl)thiazolo[5,4-e][1,2,4]triazolo[1,5-c]pyrimidine-2(3H)-thiones against neuroleptic-induced catalepsy and oxidative stress in mice

A series of 3-alkyl/aryl-8-(furan-2-yl)thiazolo[5,4-e][1,2,4]triazolo[1,5-c]pyrimidine-2(3H)-thiones (3a-3f) were synthesised in good yield and evaluated for their anti-Parkinsonian and neuroprotective potential. The structures of the synthesised compounds were confirmed on the basis of their spectral data and elemental analysis. All of the compounds were found to be active in haloperidol-induced catalepsy and oxidative stress in mice. The most active compound carried a propyl group at the 3-position of the thiazolotriazolopyrimidine nucleus while substitution with a phenyl ring produced the least active compound among the series. A computational study was carried out for the prediction of pharmacokinetic properties and none of the compounds violated Lipinski's rule of five, making them potentially promising agents for the treatment of Parkinson's disease.

Towards a reconceptualization of striatal interactions between glutamatergic and dopaminergic neurotransmission and their contribution to the production of movements

According to the current model of the basal ganglia organization, simultaneous activation of the striato-nigral direct pathway by glutamatergic and dopaminergic neurotransmission should lead to a synergistic facilitatory action on locomotor activity, while in contrast activation of the indirect pathway by these two neurotransmittions should lead to antagonistic effects on locomotor activity. Based on published data, as a break with the current thinking, we propose a reconceptualization of functional interactions between dopaminergic and glutamatergic neurotransmission. In this model, dopaminergic neurotransmission is seen as a motor pacemaker responsible for the basal and primary activation of striatal output neurons and glutamate as a driver providing a multiple combination of tonic, phasic, facilitatory and inhibitory influxes resulting from the processing of environmental, emotional and mnesic stimuli. Thus, in the model, glutamate-coded inputs would allow tuning the intrinsic motor-activating properties of dopamine to adjust the production of locomotor activity into goal-oriented movements.

Effects of a positive allosteric modulator of mGluR5 ADX47273 on conditioned avoidance response and PCP-induced hyperlocomotion in the rat as models for schizophrenia

Metabotropic glutamate receptors of the subtype 5 (mGluR(5)) are located in brain regions implicated in schizophrenia such as the cerebral cortex or the nucleus accumbens. They may therefore provide an interesting target for the treatment of psychoses. Currently available agonists of mGluR(5) are not selective, do not penetrate the brain and induce a tonic activation resulting in a rapid desensitization. Therefore, the research focus was shifted to positive allosteric modulators (PAMs). Subsequently several mGluR(5) PAMs have been discovered, e.g. ADX47273 (S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidin-1-yl}-methanone). In the present study, effects of ADX47273 (1-100mg/kg) were evaluated in rat models used for detecting antipsychotic-like activity: the conditioned avoidance response (CAR) and the phencyclidine (PCP)-induced hyperlocomotion models. Furthermore, the cataleptogenic potential of ADX47273 was compared to that of haloperidol. ADX47273 (100mg/kg) and various clinically used neuroleptics (haloperidol, olanzapine, and aripiprazole) attenuated CAR behaviour in rats. However, ADX47273 and aripiprazole failed to reduce the PCP-induced hyperlocomotion, whereas olanzapine and haloperidol diminished it. In contrast to haloperidol, ADX47273 (100mg/kg) failed to induce consistent catalepsy in rats. In conclusion, ADX47273 shows promising antipsychotic activity in some tests which require future investigation.

Sound sequence discrimination learning motivated by reward requires dopaminergic D2 receptor activation in the rat auditory cortex

We have previously reported that sound sequence discrimination learning requires cholinergic inputs to the auditory cortex (AC) in rats. In that study, reward was used for motivating discrimination behavior in rats. Therefore, dopaminergic inputs mediating reward signals may have an important role in the learning. We tested the possibility in the present study. Rats were trained to discriminate sequences of two sound components, and licking behavior in response to one of the two sequences was rewarded with water. To identify the dopaminergic inputs responsible for the learning, dopaminergic afferents to the AC were lesioned with local injection of 6-hydroxydopamine (6-OHDA). The injection attenuated sound sequence discrimination learning, while it had no effect on discrimination between the sound components of the sequence stimuli. Local injection of 6-OHDA into the nucleus accumbens attenuated sound discrimination learning. However, not only discrimination learning of sound sequence but also that of the sound components were impaired. SCH23390 (0.2 mg/kg, i.p.), a D1 receptor antagonist, had no effect on sound sequence discrimination learning, while it attenuated the licking behavior to unfamiliar stimuli. Haloperidol (0.5 mg/kg, i.p.), a D2 family antagonist, attenuated sound sequence discrimination learning, while it had no clear suppressive effect on discrimination of two different sound components and licking. These results suggest that D2 family receptors activated by dopaminergic inputs to the AC are required for sound sequence discrimination learning.

Dopamine-glutamate reciprocal modulation of release and motor responses in the rat caudate-putamen and nucleus accumbens of "intact" animals

Functional interactions between dopaminergic neurotransmission and glutamatergic neurotransmission are well known to play a crucial integrative role in the striatum, the major input structure of the basal ganglia now widely recognized to contribute to the control of motor activity and movements but also to the processing of cognitive and limbic functions. However, the nature of these interactions is still a matter of debate and controversy. This review (1) summarizes anatomical data on the distribution of dopaminergic and glutamatergic receptors in the striatum-accumbens complex, (2) focuses on the dopamine-glutamate interactions in the modulation of each other's release in the striatum-accumbens complex, and (3) examines the dopamine-glutamate interactions in the entire striatum involved in the control of locomotor activity. The effects of dopaminergic and glutamatergic receptor selective agonists and antagonists on dopamine and glutamate release as well on motor responses are analyzed in the entire striatum, by reviewing both in vitro and in vivo data. Regarding in vivo data, only findings from focal injections studies in the nucleus accumbens or the caudate-putamen of "intact" animals are reviewed. Altogether, the available data demonstrate that dopamine and glutamate do not uniformly interact to modulate each others' release and postsynaptic modulation of striatal output neurons. Depending on the receptor subtypes involved, interactions between dopaminergic and glutamatergic transmission vary as a multiple and complex combination of tonic, phasic, facilitatory, and inhibitory properties.

Blockade of nociceptin/orphanin FQ transmission in rat substantia nigra reverses haloperidol-induced akinesia and normalizes nigral glutamate release

We recently showed that pharmacological blockade of nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptors located in the substantia nigra stimulates the nigrostriatal dopaminergic pathway and motor behavior (Marti et al. J. Neurosci. 2004, 24, 6659-6666). To investigate whether such motor-stimulating action was dependent on functional dopaminergic transmission, the selective NOP receptor peptide antagonist [Nphe1,Arg14,Lys15]N/OFQ-NH2 (UFP-101) was microinjected into the substantia nigra reticulata of rats made cataleptic by systemic haloperidol administration. UFP-101 reduced haloperidol-induced akinesia as measured by immobility time in the bar test. UFP-101 also induced contralateral turning in cataleptic rats. To investigate the mechanisms involved in the anti-akinetic action of UFP-101, nigral glutamate release was monitored by microdialysis technique. The anti-akinetic action of UFP-101 correlated with normalization of nigral glutamate release, previously elevated by haloperidol injection. We conclude that endogenous N/OFQ in the substantia nigra sustains akinesia generated by impaired DA transmission and subthalamic nucleus overactivation. NOP receptor antagonists may be beneficial in the symptomatic therapy of parkinsonism, via normalization of subthalamonigral glutamatergic transmission.

Influence of CGS 21680, a selective adenosine A(2A) agonist, on the phencyclidine-induced sensorimotor gating deficit and motor behaviour in rats

RATIONALE

Recently it has been suggested that adenosine A(2A) receptor agonists may be potential antipsychotic drugs. It is, however, not clear whether these compounds may exert their antipsychotic effect without producing extrapyramidal side-effects (e.g. catalepsy, muscle rigidity, ataxia). It is known that such side-effects may be due to overactivation of the GABAergic strio-pallidal pathway, which may be estimated as an increased expression of proenkephalin (PENK) mRNA in the striatum.

OBJECTIVE

The aim of this study was to determine whether CGS 21680, a selective adenosine A(2A) receptor agonist, can reverse the disruption of prepulse inhibition (PPI) of the acoustic startle response induced by the non-competitive antagonist of NMDA receptors phencyclidine (PCP) without producing motor side-effects in rats.

RESULTS

Systemic administration of PCP (5 mg/kg) produced profound reduction of the PPI, which was reversed by CGS 21680 (1 mg/kg). CGS 21680 (0.1 and 1 mg/kg) was without effect on catalepsy, muscle rigidity and rotarod performance in rats as well as on the PENK mRNA expression in the striatum estimated by in situ hybridization. Only after the highest dose used (5 mg/kg) were signs of catalepsy (measured using a 9-cm cork test), disturbed balance and a loss of hind limb control (measured in the rotarod test) seen. Moreover, increased muscle resistance during passive extension measured mechanomyographically after this dose of CGS 21680 was observed.

CONCLUSIONS

The present results support the hypothesis that adenosine A(2A) receptor agonists may be potentially useful antipsychotic agents with the low incidence of extrapyramidal side-effects.

Effects of haloperidol on rat behavior and density of dopaminergic D2-like receptors

The present work shows the effects of a typical neuroleptic drug (haloperidol, HAL) on rat behavior (catalepsy and locomotor activity) and dopaminergic D2-like receptor densities in the hippocampus and striatum. Male Wistar rats (2-3 months old) were treated daily for 30 days with HAL (0.2 or 1mg/kg, intraperitoneally (i.p.)). At the end of treatment and 1h or 1, 3, 7 and 15 days after drug withdrawal, animals were subjected to behavioral tests and sacrificed afterwards for binding assays. The results showed that behavioral effects with both doses were significant only 1h and 1 day after withdrawal, and similar to controls at the third day. An up-regulation of D2 receptors was observed in the striatum (28% increase) but not in the hippocampus after 24h HAL (1mg/kg) withdrawal. However, an up-regulation was seen in both areas (1mg/kg) 3 days after drug withdrawal (58 and 42% increases in the hippocampus and striatum, respectively), and continued after 7 days of withdrawal only in the striatum (43 and 49% for the doses of 0.2 and 1mg/kg, respectively), suggesting the influence of dose, age, and time of drug withdrawal on these parameters. The up-regulation disappeared after 15 days of haloperidol withdrawal. Increases (72 and 140%) in constant dissociation values (K(d)) values were also observed 7 days after withdrawal. Results show differences on a time-basis between behavioral alterations and dopaminergic D2 receptors up-regulation.

The differential effect of haloperidol and repetitive induction on four immobility responses in mouse and guinea pig

The modification by haloperidol and repetitive induction on four immobility responses -- tonic immobility, cataleptic immobility, immobility by clamping the neck and dorsal immobility -- were compared in mice and guinea pigs. Without drug, three out of four responses (cataleptic, neck clamp and dorsal immobility) were induced in mice; guinea pigs displayed all four responses. Haloperidol (5 mg/kg i.p.) potentiated the three responses shown by mice, but did not potentiate the four responses in guinea pigs. In both undrugged and haloperidol-treated mice, only the cataleptic immobility response was potentiated by repetition. In guinea pigs, none of the four immobility responses was affected due to repetition, haloperidol or a combination of both. These data are discussed, considering that, although these immobility responses could be mediated by the same neurotransmitters (e.g. dopamine), they are possibly expressed in a differential manner as a function of the kind of stimulus used to trigger the response, characteristics of the species and, in some immobility responses such as cataleptic immobility, as a function of their interaction with habituation or another learning-like process.

Interaction between neuropeptide FF and opioids in the ventral tegmental area in the behavioral response to novelty

Considerable evidence has focused on the interaction between endogenous opioid peptides and the dopaminergic mesocorticolimbic system in behavioral responses to stress. Recently, it has been proposed that the CNS synthesizes and secretes neuropeptides that act as part of a homeostatic system to attenuate the effects of morphine or endogenous opioid peptides. Among these antiopioids, neuropeptide FF (NPFF) is particularly interesting since both NPFF immunoreactive-like terminals and NPFF binding sites are located in the vicinity of the dopaminergic cell bodies within the ventral tegmental area (VTA) suggesting an interaction at this level. The purpose of the present study was to evaluate the respective implication of opioid and antiopioid peptides at the level of the VTA in the locomotor response to novelty in rats. The results indicate that s.c. naloxone pretreatment, an opiate receptor antagonist, reduced locomotor activity in rats placed in a novel environment without having any effect in a familiar environment. This effect takes place in the VTA since intra-VTA administration of naloxone methobromide diminished similarly and dose-dependently the motor response to novelty. This effect is mainly dependent on opioid peptides released at VTA level since local injections of thiorphan, an inhibitor of enkephalin degradation, strongly increased locomotor response to novelty and this effect is completely prevented by the co-administration of naloxone methobromide. When injected in the VTA, NPFF is acting as an antiopioid compound, i.e. it reduces the locomotor activity triggered by exposure to novelty to the level recorded in a familiar environment. Moreover, NPFF decreased dose-dependently the potentiation of novelty-induced locomotor response produced by VTA injection of thiorphan. Taken together, these results suggest that NPFF neurons may participate at the level of the VTA to a homeostatic regulating process counteracting opioid effects induced by a mild stress such as novelty.

Behavioral effects of MK-801 on reserpine-treated mice

The effects of dizocilpine (MK-801), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, were studied on dopamine-related behaviors induced by reserpine treatments. This study focuses on behavioral syndromes that may used as models for Parkinson's disease, or tardive dyskinesia, and its response after glutamatergic blockage. Reserpine (1 mg/kg), administered once every other day for 4 days, produced increases in orofacial dyskinesia, tongue protrusion and vacuous chewing in mice, which are signs indicative of tardive dyskinesia. Reserpine also produced tremor and catalepsy, which are signs suggestive of Parkinson's disease. MK-801 (0.1 mg/kg), administered 30 min before the observation test, prevented the vacuous chewing movements, tongue protrusions and catalepsy induced by reserpine. However, MK-801 injection produced a significant increase of tremor in reserpine-treated mice. Reserpine (1 mg/kg), administered 90 min before the test and followed by apomophine injection (0.1 mg/kg) 5 min before the test, did not produce oral dyskinesia in mice. On the other hand, reserpine induced increases in tremor and catalepsy compared to control mice. MK-801 (0.1 mg/kg) administration attenuated the catalepsy and tremor induced by reserpine. Pretreatment with reserpine (1 mg/kg) 24 h before the observation test produced increases in vacuous chewing movements and tongue protrusion, as well as increases in tremor and catalepsy, whereas MK-801 (0.1 mg/kg) injection 90 min before the test reversed the effects of reserpine. These results show that reserpine produces different and abnormal movements, which are related to dose and schedule employed and can be considered as parkinsonian-like and tardive dsykinesia signs. The glutamatergic blockage produced by NMDA can restore these signs, such as vacuous chewing movements, tongue protrusions, catalepsy and tremor according to the employed model.

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.

Behavioral arrest: in search of the neural control system

Scientists have spent hundreds of years trying to understand how the brain controls movement. Why has there been so little interest in knowing how the brain STOPS movement? This review calls attention to behavioral phenomena in which an animal or human undergoes temporary total-body arrest of movement, that is, behavioral arrest (BA). These states can be actively induced by visual stimuli, by body and limb manipulations, and by drugs. Historically, these states have been considered as unrelated, and their literature does not cross-connect. What is known about the causal mechanisms is scant, limited mostly to implication of the brainstem in manipulation-induced BA and dopaminergic blockade in the striatum in the case of drug-induced BA. The possibility has not been experimentally tested that all of these states share with each other not only an active global immobility in which awkward postures are maintained, but also underlying neural mechanisms. This review identifies key brainstem, diencephalic, and basal forebrain areas that seem to be involved in causing BA. We review the evidence that suggest a possible role in BA for the following brain structures: entopeduncular nucleus, medullary and pontine reticular zones, parabrachial region, pedunculopontine nucleus and nearby areas, substantia nigra, subthalamic nucleus, ventromedial thalamic nucleus, and zona incerta. Such areas may operate as a BA control system. Confirmation of which brain areas operate collectively in BA would require testing of several kinds of BA in the same animals with the same kinds of experimental tests. Areas and mechanisms might be elucidated through a strategic combination of the following research approaches: imaging (fMRI, c-fos), lesions (of areas, of afferent and efferent pathways), chemical microstimulation, and electrical recording (of multiple units and field potentials, with an emphasis on testing coherence among areas). We suggest the working hypothesis that BA is created and sustained by coherent, perhaps oscillatory, activity among a group of basal forebrain and brainstem areas that collectively disrupt the normal spinal and supraspinal sequencing controls of reciprocal actions on the extensors and flexors that otherwise produce movement.

Neural mediation of nursing and related maternal behaviors

Nursing is the behavioral concomitant of lactation and the most generalizable maternal behavior across mammals. In lactating rats nursing often occurs in the kyphotic (upright crouched) posture; like the neuroendocrine determinants of milk synthesis and release, kyphosis requires suckling by the young. The dam's active pronurturant behaviors, such as retrieval and licking of pups, requires perioral somatosensory stimulation, which is often a precursor of kyphosis as well, and is inhibited by suckling. The sequential nature of maternal behaviors and the dissociations in their somatosensory regulation are critical to understanding their neural mediation, as exemplified by our recent work in lactating rats. We found that the caudal lateral and ventrolateral midbrain periaqueductal gray (cPAGl,vl) is a sensorimotor integration site for the kyphotic nursing posture. Destruction of the cPAGl,vl, or increased activity of the inhibitory neurotransmitter GABA within it, severely reduced kyphosis, increased nursing in more atypical postures, and had little or no effect on pronurturance. Various forebrain sites are known to mediate retrieval and licking of pups. Inhibition of dopaminergic activity in the nucleus accumbens of dams via microinfusions of a mixed D1/D2 dopamine receptor antagonist, cis-flupenthixol (FLU), dose-dependently reduced these active behaviors, while increasing nursing duration. Retrieval was inhibited, however, only by infusions of FLU that included the nucleus accumbens shell, which is reciprocally connected with other sites implicated in retrieval of pups. Thus, maternal behavior is not a unitary process but rather a complex category consisting of sequential behavioral components that have their own sensory and neural determinants.

Atropine acts in the ventral striatum to reduce raclopride-induced catalepsy

While muscarinic receptor antagonists are used to reduce motor side effects associated with the use of antipsychotic drugs, their site of action remains unclear. The study investigated the site of action of the non-selective muscarinic receptor antagonist atropine on catalepsy induced by the selective dopamine D2 receptor antagonist, raclopride. Initially, catalepsy and striatal muscarinic receptor occupancy was assessed 2 h following subcutaneous injection of raclopride and either atropine or vehicle. Catalepsy was significantly reduced by doses of atropine that occupied more than 69% of muscarinic receptors. Next, atropine was injected bilaterally into the ventral striatum, which produced a significant reduction in catalepsy, while injections into the dorsal striatum and substantia nigra had no effect. The site of atropine's action was localised to a discrete area of the ventral striatum through the use of quantitative autoradiographic techniques. These findings provide further evidence for the importance of the ventral striatum in the expression of behaviours.

Motor behavioural changes after intracerebroventricular injection of 6-hydroxydopamine in the rat: an animal model of Parkinson's disease

At the beginning of the 1970s, different studies reported behavioural disturbances after the intracerebroventricular (icv) administration of 6-hydroxydopamine (6-OHDA) in the rat. Despite the fact that this neurotoxic agent degenerates brain dopaminergic (DA-) cells, its potential utility to produce a rat model of Parkinson's disease (PD) was never systematically studied because the aphagia and adipsia were often observed. In the present study, a procedure that induces a marked DA-cell degeneration that bypasses these and other undesirable complications of icv injection of 6-OHDA is reported. Lesioned animals (50-500 microg of 6-OHDA) showed a persistent motor syndrome composed of hypokinesia, purposeless chewing and catalepsy. The intensity of motor signs was dose-dependent, and recovered partially after administration of DA-receptor agonists, exposure to sensorial stimuli and stress, three procedures that reduce motor dysfunctions in Parkinson's disease (PD). Lesioned animals showed bilateral and symmetrical midbrain DA-cell degeneration with the highest cell-loss in A9 group (substantia nigra), followed by A8 (retrorubral field) and A10 (ventral tegmental area) groups. The similarity between the behavioural syndrome and the topographical profile of cell-loss after icv injection of 6-OHDA in rats and the clinical and neuropathological features of PD indicates that this may be a convenient animal model of PD particularly useful for checking in rats the possible efficacy of new anti-parkinsonian drugs on specific parameters of motor dysfunctions.

Dopamine cell degeneration induced by intraventricular administration of 6-hydroxydopamine in the rat: similarities with cell loss in parkinson's disease

In an attempt to find a convenient rat model to study cell vulnerability in Parkinson's disease, we have investigated the cell-loss profile in different midbrain dopaminergic nuclei and subnuclei of rats injected with 6-hydroxydopamine (6-OHDA) in the third ventricle. Following administration of different doses (5-1000 microgram) of 6-OHDA, motor behavior was evaluated and tyrosine hydroxylase-immunostained neurons were counted in the A8 group and different subdivisions of A9 and A10 groups. Animals developed hypokinesia, repetitive chewing movements, and catalepsia. Signs of cell degeneration were evident from the first day after injection, reaching the definitive pattern at the end of the first week. There was a similar degeneration in both brain sides, the A9 group showing the highest degree of cell-loss, followed by A8 and A10 groups. In the A9 group, the degeneration mostly affected those subgroups located in its ventral, lateral, and posterior regions. In the A10 group the degeneration mainly affected the parabrachial pigmented nucleus, the paranigral nucleus and the ventral tegmental area. This topographic pattern of degeneration is very similar to that previously described in Parkinson's disease, suggesting that this model may be a useful tool in the study of the cell vulnerability mechanisms in this neurodegenerative disorder. In addition, our results also showed that small dopaminergic neurons are more resistant to degeneration than the large ones. In some DA subgroups, the cells that contained calbindin but not calretinin were less vulnerable to the neurotoxic effect of 6-OHDA.

Dopamine in the striatum modulates seizures in a genetic model of absence epilepsy in the rat

Inhibition of the substantia nigra pars reticulata has been shown to suppress seizures in different animal models of epilepsy. The striatum is the main input of the substantia nigra pars reticulata. The aim of the present study was to examine the role of dopaminergic neurotransmission within the striatum in the control of absence seizures in a genetic model in the rat. Injections of mixed dopaminergic D1/D2 or of selective D1 or D2 agonists or antagonists in the dorsal parts of the striatum led to suppression of absence seizures associated with strong behavioral and electroencephalographic side-effects. When injected in the ventral part of the striatum (i.e. the nucleus accumbens core), all these agonists and antagonists respectively decreased and increased absence seizures without behavioral or electroencephalographic side-effects. Combined injections of low doses of a D1 and a D2 agonist in the core of the nucleus accumbens had an additive effect in absence seizures suppression. Furthermore, combined injections of low doses of a GABA(A) agonist and a N-methyl-D-aspartate antagonist in the substantia nigra also had cumulative effects in absence seizures suppression. These results show that dopamine neurotransmission in the core of the nucleus accumbens is critical in the control of absence seizures. The modulatory and additive effects on absence seizures of dopaminergic neurotransmission through both the D1 and D2 receptors in the core of the nucleus accumbens further suggest that ventral pathways of the basal ganglia system are involved in the modulation of absence seizures.

Haloperidol catalepsy consolidation in the rat as a model of neuromodulatory integration

Haloperidol, a non-selective D(2) dopamine antagonist, both in vitro (1 microM) and in vivo (2.5 mg/kg i.p.), induced a long-term potentiation of K(+)-induced Ca(2+)-dependent release of endogenous noradrenaline and dopamine in rat brain cortical slices, by increasing the content of noradrenaline and dopamine known to be controlled by dopamine auto- and heteroreceptors. Haloperidol administration (2.5 mg/kg i.p.) evoked catalepsy and increased the content of noradrenaline and dopamine in the same structures of the brain. Haloperidol catalepsy consolidated without any additional learning and could be retrieved up to two weeks later by placing the animals in the test box. The catalepsy is disordered and retrieved only in the test box. The catalepsy was more intense on day 14 than on day 7. Injection of haloperidol immediately after conditioning evened the reflex retrieval on the following days. Moreover, learning increased the intensity of catalepsy in animals tested on the day of injection. Repeated testing of the reflex on the following days led to specific modifications of catalepsy retrieval. Pre-conditioned rats exhibited maximal catalepsy when tested immediately after being placed in the test box. These results suggest that both the processes of long-term potentiation and catalepsy consolidation are mediated by the same type of receptors, long-term modulation-inducing receptors. Endogenous neuromodulators, acting non-specifically or diffusely via their respective long-term modulation-inducing receptors, can initiate and consolidate generalized states which form the basis for emotional and motivational states.

The antidepressive-like effect of oxcarbazepine: possible role of dopaminergic neurotransmission

It has been previously shown that oxcarbazepine (OXCBZ), a keto-analogue of carbamazepine, exhibits an antidepressive-like effect profile in the learned helplessness and forced swimming test (FST). Since carbamazepine possesses dopaminergic effect, the present study was carried out to evaluate the extent to which the antidepressive effect of OXCBZ might be mediated by dopaminergic system. Thus, the effects of OXCBZ in haloperidol-induced catalepsy and apomorphine-induced stereotypy were studied. The anti-immobility effect of OXCBZ in the FST was also evaluated in haloperidol pre-treated rats. OXCBZ (40 and 80 mg/kg, i.p.) dose-dependently reduced the catalepsy induced by haloperidol (2.0 mg/kg, i.p.). Moreover, OXCBZ (80 mg/kg, but not 20 or 40 mg/kg, i.p.) increased the intensity of apomorphine-induced stereotypy (0.6 mg/kg, s.c.). Finally, it was observed that the combination of OXCBZ (80 mg/kg, i. p.) and haloperidol (0.5 mg/kg, i.p.) antagonized the anti-immobility effect of OXCBZ and further increased the immobility time when compared to haloperidol alone. Haloperidol alone (0.5 or 1. 0 mg/kg) did not change the immobility time. Thus, these results suggest that OXCBZ could enhance dopaminergic neurotransmission, which might mediate its antidepressive-like effect.

Activation of group II metabotropic glutamate receptors inhibits synaptic excitation of the substantia Nigra pars reticulata

Loss of nigrostriatal dopaminergic neurons in Parkinson's disease (PD) leads to increased activity of glutamatergic neurons in the subthalamic nucleus (STN). Recent studies reveal that the resultant increase in STN-induced excitation of basal ganglia output nuclei is responsible for the disabling motor impairment characteristic of PD. On the basis of this, it is possible that any manipulation that reduces activity at excitatory STN synapses onto basal ganglia output nuclei could be useful in the treatment of PD. We now report that group II metabotropic glutamate receptors (mGluRs) are presynaptically localized on STN terminals and that activation of these receptors inhibits excitatory transmission at STN synapses. In agreement with the hypothesis that this could provide a therapeutic benefit in PD, a selective agonist of group II mGluRs induces a dramatic reversal of catalepsy in a rat model of PD. These results raise the exciting possibility that selective agonists of group II mGluRs could provide an entirely new approach to the treatment of PD. These novel therapeutic agents would provide a noninvasive pharmacological treatment that does not involve the manipulation of dopaminergic systems, thus avoiding the problems associated with current therapies.

Quantitative prediction of catalepsy induced by amoxapine, cinnarizine and cyclophosphamide in mice

Parkinsonism can be a side effect of antipsychotic drugs, and has recently been reported with peripherally acting drugs such as calcium channel blockers, antiarrhythmic agents and so on. In this study, we examined the quantitative prediction of drug-induced catalepsy by amoxapine, cinnarizine and cyclophosphamide, which have been reported to induce parkinsonism. Dose-dependent catalepsy was induced by these drugs in mice. In vivo dopamine D(1), D(2) and muscarinic acetylcholine (mACh) receptor occupancies by these drugs in the striatum were also examined. The in vitro binding affinities (K(i) values) of amoxapine and cinnarizine to dopamine D(1), D(2) and mACh receptors in rat striatal synaptic membrane were 200 and 2900 nM, 58.4 and 76.4 nM and 379 and 290 nM, respectively. Cyclophosphamide did not bind to these receptors at concentrations up to 100 microM. Twenty drugs, including those mentioned above, showed a significant correlation between the observed intensity of catalepsy and the values predicted with a pharmacodynamic model (Haraguchi K, Ito K, Kotaki H, Sawada Y, Iga T. Prediction of drug-induced catalepsy based on dopamine D(1), D(2), and muscarinic acetylcholine receptor occupancies. Drug Metab Disp 1997; 25: 675-684) based on in vivo occupancy of dopamine D(1), D(2) and mACh receptors. We conclude that occupancy of dopamine D(1) and D(2) receptors contributes to catalepsy induction by amoxapine and cinnarizine.

The role of striatal adenosine A2A receptors in regulation of the muscle tone in rats

The aim of the present study was to assess contribution of striatal adenosine A2A receptors to regulation of the muscle tone in rats. The muscle tone was examined by a combined mechano- and electromyographic method, which measured simultaneously muscle resistance (MMG) of a rats hind foot to passive extension and flexion in the ankle joint and the electromyographic activity (EMG) of the antagonistic muscles: gastrocnemius and tibialis anterior. CGS 21680 (1 and 2 microg/0.5 microl), injected bilaterally into the rostral part of the striatum, dose-dependently increased both MMG and the EMG. The present results show that stimulation of striatal adenosine A2A receptors by CGS 21680 evokes parkinsonian-like muscle rigidity which may be due to activation of the GABAergic strio-pallidal pathway.

Dopamine D1 or D2 receptor blockade in the globus pallidus produces akinesia in the rat

In the present study, the involvement of dopamine D1 and D2 receptors in the dorsal globus pallidus (GP) in motor control was investigated in rats. Results show that bilateral microinfusions of the dopamine D1 receptor antagonist SCH23390 or the dopamine D2 antagonist S( - )-sulpiride into the GP induced akinesia determined by means of the catalepsy test. These findings indicate that pallidal dopamine D1 and D2 receptors are critically involved in the control of motor behaviour. The findings further imply that defective dopaminergic transmission in the GP might contribute to akinesia due to lesion- or drug-induced dopamine hypofunction in experimental animals and in neurodegenerative diseases, e.g. Parkinson's disease, affecting the nigrostriatal dopamine system.

Efficacy of pramipexole, a new dopamine receptor agonist, to relieve the parkinsonian-like muscle rigidity in rats

The aim of the present study was to assess the efficacy of pramipexole (2-amino-4,5,6, 7-tetrahydro-6-propyl-amino-benzthiazole-dihydrochloride), a new dopamine D(2)/D(3) receptor agonist, to attenuate parkinsonian-like muscle rigidity in rats. Muscle tone was examined using a combined mechano- and electromyographic (EMG) method, which simultaneously measured the muscle resistance of a rat's hindlimb to passive extension and flexion at the ankle joint, and the EMG acitivity of the antagonistic muscles of that joint: gastrocnemius and tibialis anterior. Muscle rigidity was produced by reserpine (5 mg/kg) injected in combination with alpha-methyl-p-tyrosine (250 mg/kg) or by haloperidol (0.5 mg/kg). Pramipexole in doses of 0.5-5 mg/kg antagonized both reserpine+alpha-methyl-p-tyrosine- and haloperidol-induced muscle rigidity. Pramipexole also reduced reserpine-enhanced tonic and reflex EMG activities in the gastrocnemius muscle. The present results suggest that stimulation of the postsynaptic dopamine receptor may be chiefly responsible for the antiparkinsonian action of pramipexole. The ability of pramipexole to diminish the parkinsonian-like muscle rigidity seems to indicate a therapeutic value of this compound in the treatment of Parkinson's disease.

Effects of diazepam or haloperidol on convulsion and behavioral responses induced by bilateral electrical stimulation in the medial prefrontal cortex

1. Effects of diazepam (DZP) or haloperidol (HAL) on convulsions and behavioral responses (locomotion, circling, spying and head shaking) induced by bilateral electrical stimulation in the medial prefrontal cortex (mPFC) were examined. 2. Male Wistar rats were electrically stimulated (ten 30-sec trains, 60 Hz, 80-100 microA) bilaterally in the mPFC and their behavior was simultaneously observed in an open field in daily session. 3. DZP and HAL dose-response curves (0, 0.5, 1.25, 2.5 and 5 mg/kg, i.p., 30 min before electrical stimulation session) were determined after a baseline of behavioral responses was established. 4. DZP dose-dependently decreased head shaking and convulsions, had no effect in circling and spying behaviors, and increased locomotion except at the highest dose. HAL reduced locomotion, circling and spying behaviors in a dose-dependent manner, but did not affect convulsions or head shaking. 5. These results demonstrated that convulsion and behavioral responses induced by electrical activation of the mPFC were modified by DZP or HAL. Therefore, the mPFC is involved in the mediation of neural and/or behavioral activity that may be implicated in some central effects of psychoactive drugs.

Dopamine receptor blockade in the nucleus accumbens inhibits maternal retrieval and licking, but enhances nursing behavior in lactating rats

Maternal behaviors were recorded in rats after a 4-h dam-litter separation and intracranial microinfusion of saline on Day 6 postpartum or cis-flupenthixol (FLU), a dopamine (DA) receptor antagonist, on Days 7-9, within the nucleus accumbens (NA) or dorsomedial striatum (DMS) bilaterally (5, 10, or 20 micro/microL/side), or the lateral ventricle (LV) unilaterally (20 or 40 micro/microL). The number of pups retrieved was inhibited in a dosage-dependent manner by FLU within the NA, but not in other sites. Pup retrieval did not occur within 5 min after 20 microg FLU in five out of nine NA dams; only in these dams did infusions include the shell region of the NA. Duration of pup licking was dose dependently decreased by FLU, the most within the NA, and to a lesser extent within the DMS. Nursing behavior in the kyphotic (upright, dorsally arched) posture, initiated in the absence of pup retrieval by placing the dam over the gathered pups, was not inhibited by intracranial FLU in any site assessed, but rather lasted longer after FLU in NA dams. These various effects of FLU, especially in NA, may be related to modest increases in catalepsy.

Blockade of dopamine D2, but not of D1 receptors in the rat globus pallidus induced Fos-like immunoreactivity in the caudate-putamen, substantia nigra and entopeduncular nucleus

In the present study, we investigated Fos-like immunoreactivity (FLI) evoked by pallidal dopamine (DA) D1 and D2 receptor blockade in the caudate-putamen (CPu), substantia nigra (SN) and entopeduncular nucleus (EP), i.e. major target areas of pallidal efferents. Results demonstrate that infusion of the selective D1 antagonist SCH23390 (1 and 4 microg/0.5 microl) into the globus pallidus (GP) did not induce FLI in the CPu, SN and EP. In contrast, intrapallidal infusion of a low dose of the selective D2 antagonist S(-)-sulpiride (15 microg/0.5 microl) induced FLI restricted to the CPu. A higher dose of intrapallidal S(-)-sulpiride (25 microg/0.5 microl) induced FLI in the CPu as well as in the SN and EP. These findings add further evidence to notion that the GP plays a central role in the basal ganglia circuitry and demonstrate an involvement of extrastriatal DA via D2 receptors.

Ligands of the NMDA receptor-associated glycine recognition site and motor behavior

Motor behavior critically depends on glutamatergic functions in the basal ganglia (BG). The dorsal and ventral striatum--the main input structures of the BG--are involved in modulation of stereotyped sniffing behavior, locomotion, catalepsy and prepulse inhibition. The effects of the NMDA receptor have been well characterized in respect to motor behavior in the past. The function of the allosteric glycine site was however disregarded until now, because brain penetrating ligands were missing. The present study summarized the motor behavioral profile of several glycine site ligands (7-chlorokynurenate, ACEA 1021, MRZ-2/576, (+) HA-966, D-cycloserine and felbamate). It is shown that through blockade of the glycine site of the NMDA receptor a distinct behavioral profile can be obtained.

Motor and learning dysfunction during postnatal development in mice defective in dopamine neuronal transmission

Mice lacking expression of tyrosine hydroxylase (TH), the first and rate-limiting enzyme of the catecholamine biosynthetic pathway, in dopaminergic neuronal cell types were generated by a transgenic rescue approach to clarify the role of dopamine signaling during postnatal development. Introduction of the TH transgene directed by the dopamine beta-hydroxylase gene promoter into TH knockout mice restored noradrenaline and adrenaline synthesis, preventing perinatal lethality and cardiac dysfunction in the knockout mice. Lack of TH expression in the cells that normally express the dopaminergic phenotype resulted in a marked reduction of dopamine accumulation in the tissues, which led to multiple behavioral abnormalities at the juvenile stage. These abnormalities were characterized by a reduction in spontaneous locomotor activity, blockade of methamphetamine-induced hyperactivity, cataleptic behavior, and defects in active avoidance learning. In contrast, development of the pituitary gland as well as production and secretion of the pituitary peptide hormones dependent on hypothalamic dopaminergic control were normally maintained, despite defective dopamine synthesis. These results demonstrate that dopamine neurotransmission is essential for controlling spontaneous and voluntary movement and associative learning during postnatal development through the nigrostriatal and mesocorticolimbic pathways.

The effects of globus pallidus lesions on dopamine-dependent motor behaviour in rats

Motor effects of bilateral lesions of the globus pallidus induced by quinolinic acid (30 and 60 nmol in 0.5 microl) were investigated in rats. Globus pallidus lesions with 60 nmol quinolinic acid produced a significant reduction of spontaneous motor activity measured by a reduced locomotor activity in an open field and by a reduced sniffing activity in an experimental chamber. In addition, D-amphetamine (1 mg/kg, i.p.)-induced hyperlocomotion and D-amphetamine (3 mg/kg, i.p.)-induced stereotyped sniffing were significantly reduced in animals with quinolinic acid lesions (60 nmol). Globus pallidus lesions with 60 nmol quinolinic acid potently reversed catalepsy induced by systemic administration of the dopamine D1 receptor antagonist SCH23390 (0.75 and 1 mg/kg, i.p.) or the dopamine D2 receptor antagonist raclopride (1.25 and 5 mg/kg, i.p.), while lesions with 30 nmol quinolinic acid exerted anti-cataleptic effects which were only partly significant. In line with current models of basal ganglia functions, these findings indicate that inactivation of the globus pallidus reduced spontaneous motor activity and motor hyperactivity after dopamine receptor stimulation. However, the present data also demonstrate that inactivation of the globus pallidus reversed motor hypoactivity induced by a blockade of dopamine D1 and D2 receptors. Therefore, a more complex functional model of the globus pallidus is required to account for the opposite effects on motor behaviour observed after lesions of this basal ganglia nucleus.

Dopamine D1- and D2-dependent catalepsy in the rat requires functional NMDA receptors in the corpus striatum, nucleus accumbens and substantia nigra pars reticulata

This study investigated the anticataleptic activity of MK-801 versus the D1 antagonist SCH 23390 and the D2 antagonist raclopride, using the horizontal bar test in the rat. MK-801, 0.2 mg/kg i.p., strongly opposed the cataleptogenic actions of SCH 23390 and raclopride administered systemically (1 and 3 mg/kg i.p., respectively), or directly into the corpus striatum (CS) or nucleus accumbens (NAc; 1 and 10 microg, respectively). Conversely, intraCS and intraNAc pretreatment with MK-801 (10 microg) markedly attenuated the cataleptic response to a systemic injection of SCH 23390 or raclopride. In the latter experiments the anticataleptic effect of MK-801 was pronounced and sustained (> 2 h), except with intraCS MK-801 versus raclopride, where it was initially profound but only short-lived (15 min). Stereotaxic injection of MK-801 (1 microg) into the substantia nigra pars reticulata (SNr) prevented catalepsy developing to either dopamine D1 or D2 receptor antagonism. These results indicate there must be unimpeded glutamate neurotransmission in the CS and NAc before catalepsy can develop fully to D1 and D2 dopamine receptor blockade in these structures. The weaker glutamate-D2 interaction in the CS than in the NAc may be related to differences in the N-methyl-D-aspartate receptor subpopulations in these nuclei. Finally, the ability of intranigral MK-801 to diminish both D1- and D2-dependent catalepsy suggests the SNr acts as a common output pathway for the expression of both forms of catalepsy in the rat.