Striatal N-methyl-D-aspartate receptors in haloperidol-induced catalepsy

Haloperidol-Induced Immediate Early Genes in Striatopallidal Neurons Requires the Converging Action of cAMP/PKA/DARPP-32 and mTOR Pathways

Antipsychotics share the common pharmacological feature of antagonizing the dopamine 2 receptor (D2R), which is abundant in the striatum and involved in both the therapeutic and side effects of this drug’s class. The pharmacological blockade of striatal D2R, by disinhibiting the D2R-containing medium-sized spiny neurons (MSNs), leads to a plethora of molecular, cellular and behavioral adaptations, which are central in the action of antipsychotics. Here, we focused on the cell type-specific (D2R-MSNs) regulation of some striatal immediate early genes (IEGs), such as cFos, Arc and Zif268. Taking advantage of transgenic mouse models, pharmacological approaches and immunofluorescence analyses, we found that haloperidol-induced IEGs in the striatum required the synergistic activation of A2a (adenosine) and NMDA (glutamate) receptors. At the intracellular signaling level, we found that the PKA/DARPP-32 and mTOR pathways synergistically cooperate to control the induction of IEGs by haloperidol. By confirming and further expanding previous observations, our results provide novel insights into the regulatory mechanisms underlying the molecular/cellular action of antipsychotics in the striatum.

Long-term effects of aripiprazole exposure on monoaminergic and glutamatergic receptor subtypes: comparison with cariprazine

OBJECTIVE

This study examined the chronic effects of aripiprazole and cariprazine on serotonin (5-HT1A and 5-HT2A) and glutamate (NMDA and AMPA) receptor subtypes. In addition, the effects of aripiprazole on D2 and D3 receptors were tested and compared with previously reported cariprazine data.

METHODS

Rats received vehicle, aripiprazole (2, 5, or 15 mg/kg), or cariprazine (0.06, 0.2, or 0.6 mg/kg) for 28 days. Receptor levels were quantified using autoradiographic assays on brain sections from the medial prefrontal cortex (MPC), dorsolateral frontal cortex (DFC), nucleus accumbens (NAc), caudate-putamen medial (CPu-M), caudate-putamen lateral (CPu-L), hippocampal CA1 (HIPP-CA1) and CA3 (HIPP-CA3) regions, and the entorhinal cortex (EC).

RESULTS

Similar to previous findings with cariprazine, aripiprazole upregulated D2 receptor levels in various regions; D3 receptor changes were less than those reported with cariprazine. All aripiprazole doses and higher cariprazine doses increased 5-HT1A receptors in the MPC and DFC. Higher aripiprazole and all cariprazine doses increased 5-HT1A receptors in HIPP-CA1 and HIPP-CA3. Aripiprazole decreased 5-HT2A receptors in the MPC, DFC, HIPP-CA1, and HIPP-CA3 regions. Both compounds decreased NMDA receptors and increased AMPA receptors in select brain regions.

CONCLUSIONS

Long-term administration of aripiprazole and cariprazine had similar effects on 5-HT1A, NMDA, and AMPA receptors. However, cariprazine more profoundly increased D3 receptors while aripiprazole selectively reduced 5-HT2A receptors. These results suggest that the unique actions of cariprazine on dopamine D3 receptors, combined with its effects on serotonin and glutamate receptor subtypes, may confer the clinical benefits, safety, and tolerability of this novel compound in schizophrenia and bipolar mania.

Effects of risperidone on glutamate receptor subtypes in developing rat brain

Levels of ionotropic glutamate (Glu) N-methyl-d-aspartic acid (NMDA), 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionic acid (AMPA), and kainic acid (KA) receptors in forebrain regions of juvenile rats (age 42 days) were quantified after 3 weeks of treatment with three different doses of risperidone (0.3, 1.0 and 3.0 mg/kg) and compared findings to those in adult rats treated with risperidone (3.0 mg/kg/day) previously. Risperidone (at 0.3 mg/kg/day) did not alter levels of three ionotropic Glu receptors in all brain regions examined. Risperidone (at 1.0 and 3.0 mg/kg/day) significantly decreased NMDA binding in caudate-putamen of juvenile and adult animals. In contrast, the same two doses of risperidone decreased NMDA receptors in nucleus accumbens of juveniles and not adults. Risperidone (at 1.0 and 3.0 mg/kg/day) increased AMPA receptors in medial prefrontal cortex and caudate-putamen of juvenile animals, whereas risperidone (at 3.0 mg/kg) increased AMPA receptors in caudate-putamen and hippocampus of adults. Kainate receptors were not altered by any dose of risperidone in any brain region examined in developing and mature animals. The findings indicate that risperidone exerts dose-dependent effects on Glu receptor subtypes in developing animals, and that Glu receptor responses to repeated administration of risperidone are different in juvenile animals than adults.

NR2A and NR2B subunit containing NMDA receptors differentially regulate striatal output pathways

Triple probe microdialysis was employed to investigate whether striatal NR2A and NR2B subunit containing NMDA receptors regulate the activity of striato-pallidal and striato-nigral projection neurons. Probes were implanted in the striatum, ipsilateral globus pallidus and substantia nigra reticulata. Intrastriatal perfusion with the NR2A subunit selective antagonist (R)-[(S)-1-(4-bromo-phenyl)-ethylamino]-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-5-yl)-methyl]-phosphonic acid (NVP-AAM077) reduced pallidal GABA and increased nigral glutamate (GLU) release whereas perfusion with the NR2B subunit selective antagonist (R-(R*,S*)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl)-1-piperidinepropanol (Ro 25-6981) reduced nigral GABA and elevated striatal and pallidal GLU release. To confirm that changes in GABA levels were because of blockade of (GLUergic-driven) tonic activity of striatofugal neurons, tetrodotoxin was perfused in the striatum. Tetrodotoxin reduced both pallidal and nigral GABA release without changing GLU levels. To investigate whether striatal NR2A and NR2B subunits were also involved in phasic activation of striatofugal neurons, NVP-AAM077 and Ro 25-6981 were challenged against a NMDA concentration able to evoke GABA release in the three areas. Both antagonists prevented the NMDA-induced striatal GABA release. NVP-AAM077 also prevented the NMDA-induced surge in GABA release in the globus pallidus, whereas Ro 25-6981 attenuated it in the substantia nigra. We conclude that striatal NMDA receptors containing NR2A and NR2B subunits preferentially regulate the striato-pallidal and striato-nigral projection neurons, respectively.

Long-term Effects of JL 13, a Potential Atypical Antipsychotic, on Ionotropic Glutamate Receptors

Changes in ionotropic glutamate (Glu) N-methyl-d-aspartic acid (NMDA), and 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionic acid (AMPA) receptors in rat forebrain regions were autoradiographically quantified after continuous infusion of JL 13 [(5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3-b][1,5]benzoxazepine fumarate] for 28 days using osmotic minipumps, and compared to the effects of representative typical (haloperidol) and atypical (clozapine, olanzapine, and risperidone) antipsychotic drugs from previous studies. Similar to other atypical and not typical antipsychotics, JL 13 decreased labeling of NMDA receptors in medial and lateral caudate-putamen (CPu; by 40%). These findings indicate that down-regulation of NMDA receptors by JL 13 and other atypical antipsychotic agents in CPu may contribute to their low risk of extrapyramidal side effects. In addition, and similar to olanzapine and risperidone, JL 13 increased AMPA receptor binding in CPu (by 42%). Changes in AMPA receptors may contribute to psychopharmacological properties of JL 13 and other atypical agents. Similar to clozapine, JL 13 did not alter levels of NMDA and AMPA receptors in hippocampus and entorhinal cortex. Long-term effects of JL 13 on ionotropic Glu receptors, as well as on other dopamine and serotonin receptors, support the atypical antipsychotic profile of this novel agent.

Acetylcholinesterase modulates stress-induced motor responses through catalytic and noncatalytic properties

BACKGROUND

Cholinergic neurotransmission notably participates in stress-induced motor responses. Here we report the contribution of alternative splicing of acetylcholinesterase (AChE) pre-mRNA to modulate these responses. More specifically, we induced stress-associated hypofunction of dopaminergic, mainly D2 dopamine receptor-mediated neurotransmission by haloperidol and explored stress induced hyperlocomotion and catalepsy, an extreme form of immobility, induced in mice with AChE deficiencies.

METHODS

Conditional transgenic (Tet/AS) mice were created with tetracycline-induced antisense suppression of AChE gene expression. Locomotion and catalepsy times were measured in Tet/AS and strain-matched control mice, under open-field exposure threat and under home-cage safety.

RESULTS

In vitro, NGF-treated PC12 cells failed to extend neurites upon Tet/AS suppression. In vivo, Tet/AS but not control mice showed stress-associated hippocampal deposits of heat-shock protein 70 and GRP78 (BiP), predicting posttranscriptional changes in neuronal reactions. Supporting this notion, their striatal cholinergic neurons demonstrated facilitated capacity for neurite extension, attributing these in vivo changes in neurite extension to network interactions. Tet/AS mice presented stress-induced hyperlocomotion. Moreover, the dopamine antagonist haloperidol induced longer catalepsy in threatened Tet/AS than in control mice. When returned to home-cage safety, Tet/AS mice showed retarded release from catalepsy.

CONCLUSIONS

Acetylcholinesterase modulates stress-induced motor responses and facilitates resumption of normal motor behavior following stress through both catalytic and noncatalytic features.

Streptozotocin-induced diabetes differentially modifies haloperidol- and γ-hydroxybutyric acid (GHB)-induced catalepsy

To examine whether dopamine-mediated behavioral effects are altered in diabetes, this study compared the cataleptic effects of the dopamine receptor antagonist haloperidol (0.032-0.56 mg/kg) and gamma-hydroxybutyric acid (GHB; 56-1000 mg/kg) in control and streptozotocin (STZ)-treated rats. Haloperidol and GHB produced catalepsy in control and diabetic rats; haloperidol was less potent in diabetic rats (D(50)=0.44 mg/kg) than in controls (D(50)=0.19 mg/kg), while GHB was more potent in diabetic rats (D(50)=392 mg/kg) than in controls (D(50)=550 mg/kg). In diabetic rats, the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist dizocilpine (0.32 mg/kg) further attenuated haloperidol-induced catalepsy (D(50)=1.2 mg/kg) and further enhanced GHB-induced catalepsy (D(50)=248 mg/kg). That haloperidol is less potent to produce catalepsy in diabetic rats is consistent with reports of altered dopamine receptor binding in diabetes.

Long-term effects of olanzapine, risperidone, and quetiapine on ionotropic glutamate receptor types: implications for antipsychotic drug treatment

Levels of ionotropic glutamate (Glu) N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and kainic acid (KA) receptors in rat forebrain regions were compared by quantitative in vitro receptor autoradiography after continuous treatment for 28 days with the atypical antipsychotics olanzapine, risperidone, and quetiapine, or vehicle controls. All three treatments significantly decreased NMDA binding in caudate-putamen (CPu; by 30, 34, and 26%, respectively) but increased AMPA receptor levels in same region (by 22, 30, and 28%). Olanzapine and risperidone, but not quetiapine, also reduced NMDA receptor labeling in hippocampal CA1 (21 and 19%) and CA3 (23 and 22%) regions. KA receptors were unaltered by any treatment in the brain regions examined. These findings suggest that the antipsychotic effects of olanzapine and risperidone may be mediated in part by NMDA receptors in hippocampus, and perhaps AMPA receptors in CPu. The findings also support the hypothesis that down-regulation of NMDA receptors by atypical antipsychotic agents in CPu contributes to their low risk of extra-pyramidal side effects. Inability of olanzapine, risperidone, and quetiapine to alter KA receptors suggests their minimal role in mediating the central nervous system actions of these drugs.

Molecular aspects of glutamate dysregulation: implications for schizophrenia and its treatment

The glutamate system is involved in many aspects of neuronal synaptic strength and function during development and throughout life. Synapse formation in early brain development, synapse maintenance, and synaptic plasticity are all influenced by the glutamate system. The number of neurons and the number of their connections are determined by the activity of the glutamate system and its receptors. Malfunctions of the glutamate system affect neuroplasticity and can cause neuronal toxicity. In schizophrenia, many glutamate-regulated processes seem to be perturbed. Abnormal neuronal development, abnormal synaptic plasticity, and neurodegeneration have been proposed to be causal or contributing factors in schizophrenia. Interestingly, it seems that the glutamate system is dysregulated and that N-methyl-D-aspartate receptors operate at reduced activity. Here we discuss how the molecular aspects of glutamate malfunction can explain some of the neuropathology observed in schizophrenia, and how the available treatment intervenes through the glutamate system.

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.

Distribution of serotonin 5-HT(2A) receptors in afferents of the rat striatum

Treatment with conventional antipsychotic drugs (APDs) is accompanied by extrapyramidal side effects (EPS), which are thought to be due to striatal dopamine D(2) receptor blockade. In contrast, treatment with atypical APDs is marked by a low incidence or absence of EPS. The reduced motor side effect liability of atypical APDs has been attributed to a high serotonin 5-HT(2A) receptor affinity coupled with a relatively low D(2) affinity. Despite the high density of 5-HT(2A) binding sites in the striatum, there are few detectable 5-HT(2A) mRNA-expressing neurons in the striatum. This suggests that most striatal 5-HT(2A) receptors are heteroceptors located on afferent axons. A combined retrograde tracer-immunohistochemistry method was used to determine the sites of origin of striatal 5-HT(2A)-like immunoreactive axons. 5-HT(2A)-like immunoreactive neurons in both the cortex and globus pallidus were retrogradely labeled from the striatum; very few nigrostriatal or thalamostriatal neurons expressed 5-HT(2A)-like immunoreactivity. Within the striatum, parvalbumin-containing interneurons displayed 5-HT(2A) immunolabeling; these neurons are the targets of cortical and pallidal projections. Our data indicate that cortico- and pallido-striatal neurons are the major source of 5-HT(2A) receptor binding in the striatum, and suggest that cortico- and pallido-striatal neurons are strategically positioned to reduce the motor side effects that accompany striatal D(2) receptor blockade or are seen in parkinsonism.

Pharmacology and behavioral pharmacology of the mesocortical dopamine system

The prefrontal cortex (PFC) has long been known to be involved in the mediation of complex behavioral responses. Considerable research efforts are directed towards refining the knowledge about the function of this brain area and the role it plays in cognitive performance and behavioral output. In the first part, this review provides, from a pharmacological perspective, an overview of anatomical, electrophysiological and neurochemical aspects of the function of the PFC, with an emphasis on the mesocortical dopamine system. Anatomy of the mesocortical system, basic physiological and pharmacological properties of neurotransmission within the PFC, and interactions between dopamine and glutamate as well as other transmitters within the mesocorticolimbic circuit are included. The coverage of these data is largely restricted to what is relevant for the second part of the review which focuses on behavioral studies that have examined the role of the PFC in a variety of phenomena, behaviors and paradigms. These include reward and addiction, locomotor activity and sensitization, learning, cognition, and schizophrenia. Although the focus of this review is on the mesocortical dopamine system, given the intricate interactions of dopamine with other transmitter systems within the PFC and the importance of the PFC as a source of glutamate in subcortical areas, these aspects are also covered in some detail where appropriate. Naturally, a topic as complex as this cannot be covered comprehensively in its entirety. Therefore this review is largely limited to data derived from studies using rats, and it is also specifically restricted to data concerning the medial PFC (mPFC). Since in several fields of research the findings concerning the function or role of the mPFC are relatively inconsistent, the question is addressed whether these inconsistencies might, at least in part, be related to the anatomical and functional heterogeneity of this brain area.

FosB in rat striatum: normal regional distribution and enhanced expression after 6-month haloperidol administration

Subcortical motor nuclei show differential expression of FosB immediate early gene products and specifically deltaFosB after short (8, 19, or 21 days) chronic exposure to typical and atypical neuroleptics represented by haloperidol and clozapine, respectively. We quantitatively examined whether there are light microscopic regional variations in area density of FosB or the truncated deltaFosB in several motor-related nuclei of adult rats receiving vehicle or long chronic (6 months) administration of either depot haloperidol or clozapine in their drinking water. In control animals the dorsomedial and ventromedial caudate-putamen nucleus (CPN) had a significantly higher density of FosB-immunoreactive cells than the dorsolateral and ventrolateral regions. The nucleus accumbens (NAc) core also serving motor functions had a higher basal expression than the limbic shell region in control animals. The mediolateral gradient in area density of FosB-labeled cells was maintained in animals receiving either haloperidol or clozapine. In animals receiving haloperidol, but not clozapine, however, there was a regionally selective increase in the area density of only FosB-immunoreactive neurons in the dorsolateral and ventrolateral CPN and in both the core and shell of the NAc. Only the animals receiving chronic haloperidol showed vacuous chewing movements, the animal equivalent of tardive dyskinesia in humans. Our results suggest that, whereas the medial striatal neurons are activated under basal conditions, long chronic haloperidol induced FosB expression more exclusively in the lateral CPN and NAc core, implicating these regions specifically in the motor side effects of this drug.

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.

Intracellular modulation of NMDA receptor function by antipsychotic drugs

The present study deals with the functional interaction of antipsychotic drugs and NMDA receptors. We show that both the conventional antipsychotic drug haloperidol and the atypical antipsychotic drug clozapine mediate gene expression via intracellular regulation of NMDA receptors, albeit to different extents. Data obtained in primary striatal culture demonstrate that the intraneuronal signal transduction pathway activated by haloperidol, the cAMP pathway, leads to phosphorylation of the NR1 subtype of the NMDA receptor at (897)Ser. Haloperidol treatment is likewise shown to increase (897)Ser-NR1 phosphorylation in rats in vivo. Mutation of (896)Ser and (897)Ser to alanine, which prevents phosphorylation at both sites, inhibits cAMP-mediated gene expression. We conclude that antipsychotic drugs have the ability to modulate NMDA receptor function by an intraneuronal signal transduction mechanism. This facilitation of NMDA activity is necessary for antipsychotic drug-mediated gene expression and may contribute to the therapeutic benefits as well as side effects of antipsychotic drug treatment.

Differential effects of haloperidol and clozapine on ionotropic glutamate receptors in rats

Despite multiple lines of investigation the effect of neuroleptics on glutamate-mediated neurotransmission remains controversial. To study the effects of typical and atypical neuroleptics on selected parameters of glutamate-mediated neurotransmission, male Sprague-Dawley rats were randomly assigned to a 21-day oral treatment course with vehicle, haloperidol (HDL), or clozapine (CLZ). Coronal slices of rat brain were then incubated with tritiated ligands to measure NMDA, AMPA, and kainate receptor, and glutamate reuptake site density. Regions of interest included the frontal cortex, anterior cingulate cortex, dorsal striatum, ventral striatum, and the nucleus accumbens. CLZ increased the density of AMPA receptors significantly in the frontal and anterior cingulate cortices compared with normal controls. In the dorsal and ventral striatum, and nucleus accumbens as a whole, CLZ-treated rats had a higher AMPA receptor density compared with both the HDL- and vehicle-treated controls. Additionally, within the nucleus accumbens, CLZ-treated rats had a higher density of AMPA receptors compared with the HDL group in the core, and at trend level in the shell. There was a group by region interaction for NMDA receptor density, primarily reflecting the tendency of HDL treated rats to have high receptor densities in the frontal and anterior cingulate cortices. Kainate receptors and glutamate reuptake site densities did not differ significantly across groups. These results suggest a critical role for glutamate in the mediation of atypical antipsychotic drug action in anatomically-specific regions, and further encourage the investigation of glutamate neurotransmitter systems in schizophrenia.

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.

Contribution of the glycine site of NMDA receptors in rostral and intermediate-caudal parts of the striatum to the regulation of muscle tone in rats

The aim of the present study was to assess the contribution of the glycine site of NMDA receptors in the striatum to the regulation of muscle tone. Muscle tone was examined using a combined mechanoand electromyographic method, which measured simultaneously the muscle resistance (MMG) of the rat's hind foot to passive extension and flexion in the ankle joint and the electromyographic activity (EMG) of the antagonistic muscles of that joint: gastrocnemius and tibialis anterior. Muscle rigidity was induced by haloperidol (2.5 mg/kg i.p.). 5,7-dichlorokynurenic acid (5,7-DCKA), a selective glycine site antagonist, injected in doses of 2.5 and 4.5 microg/0.5 microl bilaterally, into the rostral region of the striatum, decreased both the haloperidol-induced muscle rigidity (MMG) and the enhanced electromyographic activity (EMG). 5,7-DCKA injected bilaterally in a dose of 4.5 microg/0.5 microl into the intermediate-caudal region of the striatum of rats not pretreated with haloperidol had no effect on the muscle tone. The present results suggest that blockade of the glycine site of NMDA receptors in the rostral part of the striatum may be mainly responsible for the antiparkinsonian action of this drug.

Evidence for a striatal NMDA receptor modulation of nigral glutamate release. A dual probe microdialysis study in the awake freely moving rat

Dual probe microdialysis was employed to characterize dialysate glutamate levels from the substantia nigra pars reticulata of awake freely moving rats, and to test its sensitivity to alterations in striatal neurotransmission including striatal N-methyl-D-aspartic acid (NMDA) receptor stimulation and blockade. Intranigral perfusion with low (0.1 mM) Ca2+ medium (60 min) did not affect nigral glutamate levels, whereas intranigral perfusion with tetrodotoxin (10 microM, 60 min) increased nigral glutamate levels. Perfusion of KCI (100 mM, 10 min) in the dorsolateral striatum transiently stimulated nigral glutamate levels (maximal increase + 60%), whereas intrastriatal perfusion (60 min) with low Ca2+ medium and tetrodotoxin gradually increased nigral glutamate levels. Intrastriatal perfusion with NMDA (0.1-100 microM, 10 min) dose-dependently stimulated glutamate levels in the substantia nigra pars reticulata. The NMDA (1 microM)-induced increase in nigral glutamate release was transient and maximal (+60% within 20 min), whereas that for NMDA (10 microM) had a slow onset but was long lasting (+35% after 60 min). Lower (0.1 microM) and higher (100 microM) NMDA concentrations were ineffective. The effect of intrastriatal NMDA (1 microM) was prevented by coperfusion with MK-801 (1 microM). Intrastriatal MK-801 (10 microM) alone gradually increased glutamate levels up to +50% after 60 min of perfusion. The present results suggest that glutamate levels in the substantia nigra pars reticulata are sensitive to changes in neuronal transmission in the dorsolateral striatum, and that striatal NMDA receptors regulate nigral glutamate release in both a tonic and phasic fashion.

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.

Effect of adenosine and some of its structural analogues on the conductance of NMDA receptor channels in a subset of rat neostriatal neurones

1. In order to investigate the modulatory effects of adenosine on excitatory amino acid projections onto striatal medium spiny neurons, whole-cell patch clamp experiments were carried out in rat brain slices. The effects of various agonists for P1 (adenosine) and P2 (ATP) purinoceptors and their antagonists were investigated. The A2A receptor agonist 2-p-(2-carboxyethyl)phenythylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680; 0.1 microM), the A1 receptor agonist 2-chloro-N6-cyclcopentyladenosine (CCPA; 10 microM) and the non-selective P1 purinoceptor antagonist 8-(p sulphophenyl)-theophylline (8-SPT; 100 microM) did not alter the resting membrane potential, the threshold current necessary to elicit an action potential, the amplitude of spikes, their rise time, the amplitude of the afterhyperpolarization (AHP) and the time to peak of the AHP. 2. N-methyl-D-aspartate (NMDA; 1-1000 microM) caused a concentration-dependent inward current which was larger in the absence than in the presence of Mg2+ (1.3 mM). In a subset of striatal neurones, the current response to NMDA (10 microM) and the accompanying increase in conductance were both inhibited by CGS 21680 (0.01-1 microM). The effect of CGS 21680 (0.1 microM) persisted in the presence of tetrodotoxin (0.5 microM) or in a Ca(2+)-free medium, under conditions when synaptically mediated influences may be negligible. 3. The A3 receptor agonist N6-2-(4-aminophenyl)ethyladenosine (APNEA; 0.1-10 microM) also diminished the effect of NMDA (10 microM), while the A1 receptor agonists CCPA (0.1-10 microM) and (2S)-N6-[2-endonorbornyl] adenosine [S(-)-ENBA; 10 microM] as well as the endogenous, non-selective P1 purinoceptor agonist adenosine (100 microM) were inactive. The endogenous non-selective P2 purinoceptor agonist ATP (1000 microM) also failed to alter the current response to NMDA (10 microM). Adenosine (100 microM), but not ATP (1000 microM) became inhibitory after blockade of nucleoside uptake by S[4-nitrobenzyl)-6-thioguanosine (NBTG; 30 microM). 4. 8-(p-Sulphophenyl)-theophylline (8-SPT; 100 microM), as well as the A2A receptor antagonist 8-(3-chlorostyryl) caffeine (CSC; 1 microM) and the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) at 0.03, but not 0.003 microM abolished the inhibitory action of CGS 21,680 (0.1 microM). None of these compounds altered the effect of NMDA (10 microM) by itself. DPCPX (0.03 microM) prevented the inhibition of APNEA (10 microM). 5. There was no effect of CGS 21,680 (0.1 microM), when guanosine 5'-O-(3-thiodiphosphate (GDP-beta-S; 300 microM) was included in the pipette solution in order to block G protein-mediated reactions. 6. In conclusion, adenosine receptors, probably of the A2A-subtype, inhibit the conductance of NMDA receptor channels in a subset of medium spiny neurones of the rat striatum by a transduction mechanism which involves a G protein.

MK 801 reverses haloperidol-induced catalepsy from both striatal and extrastriatal sites in the rat brain

The present study investigated whether the anticataleptic effect of (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten-5,10-imine (MK 801) is due to a blockade of N-methyl-D-aspartate (NMDA) receptors in striatal output pathways as well as in the striatum. Catalepsy induced by haloperidol (1 mg/kg i.p.) was more effectively reversed by MK 801 (0.2 mg/kg i.p.) given 10 min prior to rather than 45 min after the neuroleptic. Catalepsy evoked by intrastriatal haloperidol (7 micrograms/side) was also strongly attenuated by systemic MK 801 (0.2 mg/kg i.p.). We also found that the cataleptic rigidity induced by systemic haloperidol (1 mg/kg i.p.) could be prevented by prior injection of MK 801 into the striatum (10 micrograms), subthalamic nucleus (5 micrograms), entopeduncular nucleus (5 micrograms) or substantia nigra pars reticulata (1 microgram). These results suggest that the anticataleptic action of systemic MK 801 versus haloperidol, is due to the blockade of NMDA receptors in the striatum as well as in striatal output circuits through the subthalamus. However, systemic MK 801 (0.2 mg/kg i.p.) was without effect on the catalepsy elicited by injecting muscimol into the globus pallidus (25 ng) or ventromedial thalamus (50 ng). These findings suggest that MK 801 has little influence over thalamic excitatory feedback to the cortex, and that hypoactivity of the pallidum may not be a prerequisite for hyperactivity in the subthalamus.

Behavioural pharmacology of glutamate receptors in the basal ganglia

Glutamate receptors play a major role in the transmitter balance within the basal ganglia (BG). N-methyl-D-aspartate (NMDA) receptor stimulation within the striatum acts behaviourally depressant while intrastriatal as well as systemic administration of NMDA receptor-antagonists have rather stimulatory effects despite the different profiles of non-competitive-, competitive NMDA receptor- and glycine site-antagonists. In animal models of Parkinson's disease all these NMDA receptor antagonists counteract parkinsonian symptoms or act synergistically with L-3,4-dihydroxyphenylalanine (L-DOPA). The strong locomotion-inducing effect of the non-competitive NMDA receptor antagonists is partly, but not fully, mediated by a dopamine (DA) release in the nucleus accumbens. Manipulations at alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors produce poor behavioural effects. These, however, are different or even opposed to NMDA receptor mediated effects. Local infusions of AMPA receptor-antagonists into the BG output nuclei have an anti-parkinsonian effect but systemic injections are ineffective. These drugs even counteract the anti-parkinsonian effect of DA agonists and of non-competitive NMDA receptor antagonists as well as the DA releasing effects of the latter drugs. Only few data on the role of metabotropic receptors exist but the different receptor subtypes with different regional distribution represent a promising target for pharmacological interventions.

Antiparkinsonian and other motor effects of flupirtine alone and in combination with dopaminergic drugs

In this study we attempted to specify the behavioural profile of the analgesic flupirtine (1, 10 and 20 mg/kg p.o.) in the rat with respect to (i) its antiparkinsonian potential alone and as an adjunct to L-dihydroxyphenylalanine (L-DOPA) in the haloperidol-induced catalepsy (0.5 mg/kg haloperidol i.p.), (ii) locomotion and exploratory behaviour in the open field with holeboard, and (iii) possible psychomotor stimulating effects in the experimental chamber. In the two latter tests, behaviour was additionally challenged by D-amphetamine (2 mg/kg i.p.). In the catalepsy tests (horizontal bar, podium, grid) flupirtine alone was anticataleptic at doses of 10 and 20 mg/kg p.o., and the antiparkinsonian potential of a subthreshold dose of L-DOPA (50 mg/kg p.o.) was potentiated by 1 and 10 mg/kg p.o. flupirtine. On spontaneous forward locomotion in the open field with holeboard, flupirtine (1 and 10 mg/kg p.o.) had no marked effect but increased the frequency and duration of head dips, indicative for augmenting exploratory behaviour. Spontaneous rearing was reduced and D-amphetamine-induced rearing was enhanced by 1 mg/kg p.o. flupirtine. Grooming was reduced by 1 and 10 mg/kg p.o. flupirtine. In contrast, turning and grooming behaviour (spontaneous as well as D-amphetamine-induced) was not markedly influenced by flupirtine in the experimental chamber. Sniffing was increased in this test by 1 mg/kg p.o. flupirtine but not by the higher dose. Flupirtine is highly effective in antagonising neuroleptic-induced catalepsy as well as in potentiating L-DOPA treatment in the rat, suggesting it is a prospective new candidate for the therapy of Parkinson's disease.

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

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

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

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

Stimulation of glutamate receptors in the intermediate/caudal striatum induces contralateral turning

The aim of the present study was to investigate the role of striatal NMDA, kainate and AMPA receptors in the turning behaviour of rats. N-methyl-D-aspartate (NMDA, 500 ng/0.5 microliters), kainic acid (50 ng/0.5 microliters) or alpha-amino-3-hydroxy-5-methyl-4-isoxasole- propionic acid (AMPA, 1000 ng/0.5 microliters), injected into the intermediate and caudal parts of the caudate-putamen, induced contralateral head turns and rotations. This effect was delayed or was not observed after administration of the compounds into the globus pallidus. The antagonist of non-NMDA receptors, 6,7-dinitroquinoxaline-2,3-dione (DNQX, 1000 ng/0.5 microliter), antagonized the contralateral head turns and rotations induced by AMPA (1000 ng/0.5 microliter) or kainic acid (50 ng/0.5 microliter), and evoked per se (2000 ng/0.5 microliter) the ipsilateral head turns and rotations. The NMDA receptor antagonist, (+/-)-2-amino-5-phosphonopentanoic acid (AP5, 1000 ng/0.5 microliter), induced mainly ipsilateral head turns and rotations; when injected in a dose of 500 ng/0.5 microliters, it inhibited the contralateral head turns and rotations after NMDA. The results seem to suggest that the contralateral head turns and rotations induced by stimulation of NMDA, AMPA and kainate receptors in the intermediate and caudal parts of the caudate-putamen may result from activation of the gamma-aminobutyrate (GABA)-ergic strionigral pathway.

Chronic treatment with a classical neuroleptic alters excitatory amino acid and GABAergic neurotransmission in specific regions of the rat brain

The purpose of the following experiments was to describe some of the neurochemical changes that occur in the basal ganglia of rats exposed chronically to a classical neuroleptic, fluphenazine, and to relate these changes to extrapyramidal motor dysfunction. For these studies a combination of behavioural, receptor autoradiographic and in situ hybridization methods were employed. Preliminary pharmacological studies on GABA receptors showed that incubation in Tris-acetate rather than Tris-citrate buffer increased the number of binding sites labelled by [3H]muscimol by over 120% without affecting binding affinity or selectivity. The results of experiments with fluphenazine showed that treatment for six months increased the frequency of vacuous chewing movements compared to controls. In the striatum, changes in GABA transmission were observed in fluphenazine-treated rats with increases in glutamate decarboxylase mRNA levels in the caudate nucleus, dorsal shell and core of the accumbens and decreases in [3H]muscimol binding in the caudate and dorsal shell regions. These data suggest that fluphenazine treatment increased GABA transmission in specific subregions of the caudate and accumbens nuclei. In addition, glutamate decarboxylase mRNA levels were elevated in the entopeduncular nucleus of fluphenazine-treated animals. Autoradiographic analysis of excitatory amino acid binding showed that fluphenazine exposure decreased [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding in entopeduncular nucleus and in the ventrolateral thalamic nucleus and decreased [3H]dizocilpine maleate binding in the medial geniculate nucleus. These experiments show that in addition to altering GABA transmission, chronic neuroleptic exposure alters excitatory amino acid transmission in specific regions of the basal ganglia-thalamocortical motor system. The neuroleptic dependent increases in glutamate decarboxylase mRNA levels in the entopeduncular nucleus may reflect changes in neurotransmission in the indirect pathway connecting the major input and output nuclei of the basal ganglia. Changes in some of these brain regions may be related to the occurrence of extrapyramidal motor disturbances.

Are NMDA antagonistic properties relevant for antiparkinsonian-like activity in rats?--case of amantadine and memantine

Amantadine (25, 50, 100 mg/kg), memantine (5, 10, 20 mg/kg) and MK-801 (0.05, 0.1, 0.2 mg/kg), all having NMDA channel blocking properties, were compared in three tests used for screening of antiparkinsonian agents in rats, namely: haloperidol-induced catalepsy, locomotor activity in monoamine depleted rats and rotation in rats with a unilateral substantia nigra lesion. Additionally, plasma levels of amantadine and memantine were assessed to gain an insight into the concentration ranges achieved at behaviorally active doses. Amantadine and (+)-MK-801 produced dose-dependent inhibition of haloperidol-induced catalepsy while memantine was less efficacious producing clear-cut anticataleptic action at a dose of 10 mg/kg only but failing at 20 mg/kg due to myorelaxant activity. All agents attenuated sedation in monoamine depleted rats with amantadine being the least and MK-801 being the most effective. The same rank order of efficacy was seen in inducing ipsilateral rotations in rats after a substantia nigra lesion. On the basis of the present study and published data, it can be assumed that the doses of amantadine, memantine and MK-801 showing antiparkinsonian-like activity in animals result in plasma levels leading to NMDA antagonism. However, in the haloperidol-induced catalepsy test the efficacy of amantadine was higher than memantine, while the opposite was true for rotation and reserpine-induced sedation indicating pharmacodynamic differences between both agents.

N-methyl-D-aspartate receptor blockade impairs behavioural performance of rats in a reaction time task: new evidence for glutamatergic-dopaminergic interactions in the striatum

The effects of blocking glutamate transmission at the N-methyl-D-aspartate receptor subtype were studied in rats performing a conditioned reaction time motor task. Rats were trained to release a lever after the onset of a visual stimulus within a time limit to obtain food reward. The results showed that the performances of the groups receiving the N-methyl-D-aspartate receptor antagonists dizocilpine maleate (0.1 mg/kg) injected systemically or DL-2-amino-5-phosphonovaleric acid at the highest dose tested (5.0 micrograms/microliter/side) injected locally into the striatum changed significantly as compared to controls. The effects of these antagonists, consisting of an increase in the number of lever releases occurring before the visual stimulus onset ("anticipated responses"), were similar to those induced by injecting dopamine into the same striatal location. Both dizocilpine maleate and DL-2-amino-5-phosphonovaleric acid (5.0 micrograms/microliter) reversed the motor deficits, resulting in an increase in the number of lever releases after the time limit ("delayed responses") that were induced by the D2 dopamine receptor antagonist raclopride. Although these results partly confirm the existence of a functional antagonism between the glutamatergic and the dopaminergic systems in the striatum, opposite findings were obtained with the group that received intrastriatal DL-2-amino-5-phosphonovaleric acid at the lowest dose (0.5 micrograms/microliter/side). When given alone, 0.5 micrograms/microliter DL-2-amino-5-phosphonovaleric acid had no behavioural effects, but when jointly administered with dopamine or raclopride, it was found to reverse the effects of dopamine and to potentiate the motor deficits induced by raclopride. These opposite effects on the reaction time task observed after the intrastriatal injection of DL-2-amino-5-phosphonovaleric acid, depending on the dose tested, occurred only after a combined treatment with a dopaminergic agonist or antagonist and suggest that the level of the striatal dopaminergic activity may play a critical role in regulating the glutamate transmission via the N-methyl-D-aspartate receptors during the performance of complex sensorimotor tasks of this kind.

Functional interactions between glutamate and dopamine in the rat striatum

The functional role of NMDA receptors in a spontaneous (locomotion) and a conditioned behaviour (reaction-time task) known to preferentially involve dopamine transmission in the ventral or the dorsal part of the striatum, respectively, was studied in the rat. The non-competitive NMDA receptor antagonist MK-801 systemically injected produced a dose-dependent increase in locomotor activity and impaired the performance of the animals trained to release a lever after a visual stimulus within a time limit by increasing the number of anticipatory errors (lever releases occurring before the stimulus onset). Similar behavioural changes were obtained after bilateral striatal microinjections of the competitive NMDA-antagonist APV into the ventral or dorsal striatum, respectively, suggesting that MK-801-induced behavioral effects after systemic injection might be mediated through a blockade of EAA transmission within the striatum. Dopamine injected in the same striatal locations induced effects similar to APV on locomotion and reaction-time performance, in agreement with the proposal for a functional antagonism between the glutamatergic and the dopaminergic transmission at striatal level. The conjoint administration of APV and dopamine directly into the striatum did not alter the behavioural effect induced by each compound injected alone showing that these effects are not additive. This latter observation actually suggests the occurrence of a functional interaction between the two neuronal systems probably acting on a common striatal target relaying dopaminergic and glutamatergic antagonistic influences on locomotion and conditioned motor behaviours.

Haloperidol-induced morphological changes in striatum are associated with glutamate synapses

Sub-chronic treatment with the typical neuroleptic, haloperidol (0.5 mg/kg/d, s.c.), but not the atypical neuroleptic, clozapine (35 mg/kg/day, s.c.), causes an increase in synapses containing a perforated postsynaptic density (referred to as 'perforated' synapses) and in dopamine (DA) D2 receptors within the caudate nucleus [46]. To determine if these perforated synapses are glutamatergic, we systemically co-administered MK-801 (0.3 mg/kg/day for 2 weeks), a non-competitive antagonist at the N-methyl-D-aspartate (NMDA) receptor-associated ion channel, and haloperidol. MK-801 blocked the haloperidol-induced increase in striatal perforated synapses, but not the haloperidol-induced increase in DA D2 receptors. Injection of MK-801 into the striatum also attenuated the haloperidol-induced increase in perforated synapses. Post-embedding immuno-gold electron microscopy using antibodies to glutamate indicated that the gold particles were localized within striatal presynaptic nerve terminals that make contact with perforated postsynaptic densities. These findings support the hypothesis that the haloperidol-induced increase in perforated synapses is regulated by the NMDA subtype of excitatory glutamate receptor. The increase in perforated synapses following administration of haloperidol, which is associated with a high incidence of extrapyramidal side effects (EPS), and the lack of a synaptic change following administration of clozapine, known to have a low frequency of EPS, suggests that glutamate synapses play a role in the motoric side effects that are observed with typical neuroleptic drug treatment.

Glycine site antagonists abolish dopamine D2 but not D1 receptor mediated catalepsy in rats

Catalepsy--a state of postural immobility (akinesia) with muscular rigidity (rigor)--and reduced locomotion in animals are behavioral deficits showing similarities with symptoms of Parkinson's disease (PD). The effects of the glycine site antagonists 7-chlorokynurenate and (R)-HA-966 on haloperidol-(D 2 antagonist) and SCH 23390- (D 1 antagonist) induced catalepsy and reduced locomotion are investigated in rats. Both antagonists dose-dependently counteract dopamine D 2 receptor mediated catalepsy but they have no influence on locomotion. Neither 7-chlorokynurenate nor (R)-HA-966 has any effect on dopamine D 1 receptor mediated catalepsy. This finding is surprising, since NMDA receptor antagonists counteract both, dopamine D 1 and D 2 receptor mediated catalepsy. D 1 and D 2 receptors are located on different populations of neurons. Thus, the present findings suggest that these different neuronal populations have different sensitivity for ligands binding at the glycine binding site of the NMDA receptor.

Antiparkinsonian action of MK-801 on the reserpine-induced rigidity: a mechanomyographic analysis

MK-801, a non-competitive antagonist of NMDA receptors, is known to exhibit a beneficial action in many animal models of Parkinson's disease. The aim of this study was to examine the influence of MK-801 on the reserpine-induced muscle rigidity. The rigidity was estimated by a direct mechanomyographic method. This method consists in successive bending and straightening of a rat's hind foot in the ankle joint and measuring the resistance of the foot to passive movements. Reserpine in doses of 5-10 mg/kg ip, given alone or in combination with alpha-methyl-p-tyrosine (alpha MT, 250 mg/kg ip), induced rigidity. The strongest muscle rigidity was induced by 10 mg/kg of reserpine 1 hour after administration. MK-801 (0.32-1.28 mg/kg sc) injected 70 min after reserpine (10 mg/kg ip) decreased the rigidity induced by the latter compound. Similarly, MK-801 (1.28 mg/kg sc), administered 27 h 40' after joint treatment with reserpine (10 mg/kg ip) and alpha MT (250 mg/kg ip), strongly inhibited the reserpine-induced muscle rigidity. The obtained results show that the glutamatergic hyperactivity plays a significant role in the reserpine-induced rigidity. As the reserpine-induced motor disturbances are commonly accepted to be an animal model of parkinsonian symptoms, it may be assumed that the NMDA receptor blocking component may contribute substantially to the therapeutic action of antiparkinsonian drugs.

Motor activation in short- and long-term reserpinized mice: role of N-methyl-D-aspartate, dopamine D1 and dopamine D2 receptors

The effects of dopamine D1 and dopamine D2 receptor agonists and of subconvulsant doses of N-methyl-D-aspartate (NMDA) and the non-competitive NMDA receptor antagonist, dizocilpine (MK-801), alone and in combination, on the motor activity of short- and long-term reserpinized mice (mice pretreated with 5 mg/kg reserpine 4 h or 20 h before, respectively) were analyzed. With short-term reserpinization, the dopamine D2 receptor agonist, quinpirole (1.5 mg/kg), but not the dopamine D1 receptor agonist, SKF-38393 (15 mg/kg), increased motor activity. The effect of quinpirole in short-term reserpinized mice was potentiated by the simultaneous administration of SKF-38393 (15 mg/kg) and was counteracted by the previous administration of the dopamine D2 receptor antagonist, raclopride (1 mg/kg), or by the simultaneous administration of NMDA (25 mg/kg) or MK-801 (0.5 mg/kg). Neither NMDA (25-100 mg/kg) nor MK-801 (0.5-3 mg/kg) induced motor activation in short-term reserpinized mice. With long-term reserpinization, either quinpirole (1.5 mg/kg) or SKF-38393 (15 mg/kg) increased motor activity. The effect of quinpirole in long-term reserpinized mice was not potentiated by the concurrent administration of SKF-38393 (15 mg/kg), was inhibited by the simultaneous administration of MK-801 (0.5 mg/kg) and was not modified by NMDA (25 mg/kg). The effect of SKF-38393 (15 mg/kg) in long-term reserpinized mice was inhibited by the concomitant administration of MK-801 (0.5 mg/kg) and was slightly antagonized by NMDA (25 mg/kg). NMDA induced motor activation in long-term reserpinized mice at doses which were similar to those causing motor activation in non-reserpinized mice (75 and 100 mg/kg), while MK-801 induced motor activation at a dose which was associated with motor depression in non-reserpinized mice (2 mg/kg). The NMDA-induced motor activation in long-term reserpinized mice was counteracted by the previous administration of a low dose of MK-801 (0.5 mg/kg) and was still present when a stronger dopamine-depleting pretreatment was used. These results are interpreted on the basis of changes in sensitivity of the direct striatal efferent pathway after long-term reserpinization.

Distinct sites of dopaminergic and glutamatergic regulation of haloperidol-induced catalepsy within the rat caudate-putamen

Previous studies have indicated that corticostriatal glutamatergic pathways are implicated in the regulation of neuroleptic catalepsy. To obtain a better understanding of the way in which dopamine (DA) and glutamate interact within the caudate-putamen (CP) in the development of catalepsy, we investigated the regional distribution within the rat CP of the cataleptogenic effect of haloperidol and its antagonism by D(-)-2-amino-5-phosphonopentanoic acid (D(-)AP5), a selective antagonist of the N-methyl-D-aspartate (NMDA) glutamate receptor subtype. Bilateral injections of haloperidol (3 micrograms/side) into the rostral ventromedial (VM) CP induced potent catalepsy with a short latency after the injection. In contrast, only a weak cataleptic response, of slower onset, was observed after haloperidol injections into the rostral ventrolateral (VL), rostral dorsomedial (DM), or rostral dorsolateral (DL) CP, or into the nucleus accumbens. D(-)AP5 (5 micrograms/side) injected bilaterally into the dorsorostral CP (DM and DL) strongly inhibited the catalepsy induced by systemic haloperidol (1 mg/kg, i.p.), and this effect lasted longer when the drug was injected into the DM than when it was injected into the DL. D(-)AP5 did not affect haloperidol-induced catalepsy when injected into the ventrorostral (VM and VL) or intermediate dorsal CP. D(-)AP5 injected into the DM, the region most sensitive to the anticataleptic effect of the drug, had no effect on basal levels of DA and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, or on the modification of these levels by haloperidol in either the DM or VM. These findings suggest that, while the catalepsy resulting from DA receptor blockade by haloperidol originates mainly from the VM, the expression of this phenomenon depends on an intact glutamatergic transmission within the dorsorostral CP. In the development of neuroleptic catalepsy, the mesencephalostriatal DAergic and corticostriatal glutamatergic pathways seem to be functionally linked through an indirect, rather than a direct, interaction.

The role of excitatory amino acids in experimental models of Parkinson's disease

The aim of this article was to review the recent literature on the role of excitatory amino acids in Parkinson's disease and in animal equivalents of parkinsonian symptoms. Effects of NMDA and AMPA antagonists on the reserpine-induced akinesia, catalepsy and rigidity, on the neuroleptic-induced catalepsy, on the turning behaviour of 6-OHDA-lesioned rats, as well as on the parkinsonian symptoms evoked by MPTP in monkeys were analysed. Moreover, the role of NMDA antagonists in Parkinson's disease was discussed. Data concerning the protective influence of these drugs on degenerative properties of methamphetamine, MPTP and 6-OHDOPA were also presented. On the basis of the above findings, the following conclusions may be drawn: (1) disturbances in the glutamatergic transmission in various brain structures seem to play a significant role in the development of symptoms of Parkinson's disease; (2) the NMDA-receptor blocking component may make a substantial contribution to the therapeutic effect of antiparkinsonian drugs; a similar contribution of AMPA-receptor blocking component has not been sufficiently documented, so far; (3) compounds blocking NMDA receptors may possibly prevent the development of Parkinson's disease; this presumption needs, however further studies; (4) side effects of NMDA receptor antagonists may be a limiting factor in the use of these compounds in humans.

Dopamine increase in the prefrontal cortex correlates with reversal of haloperidol-induced catalepsy in rats

The mechanism by which forced swimming reverses, haloperidol-induced catalepsy was examined by measuring dopamine (DA) turnover in the nucleus accumbens-ventromedial caudate (NAC-C) and the prefrontal cortex (PFC) in rats. DA and its metabolites 3,4-dihydroxiphenylacetic acid (DOPAC) and homovanillic acid (HVA) were assessed by microdialysis and high pressure liquid chromatography with electrochemical detection (HPLC-ED) after systemic administration of a cataleptic dose of haloperidol (5 mg/kg) or saline. Haloperidol-induced catalepsy was temporarily suppressed by forced swimming. Haloperidol-treated rats showed an increase of DA, DOPAC, and HVA overflow in the PFC and the NAC-C. This increase was greater in the PFC of rats that were forced to swim. Rats that were not treated with haloperidol but were forced to swim (control group) showed an increase of DA, DOPAC, and HVA in the PFC but not in the NAC-C. Zero micrograms, 5 micrograms, 10 micrograms, and 20 micrograms of DA was bilaterally injected in the PFC of cataleptic rats to evaluate the hypothesis that DA in the PFC reverses catalepsy. Haloperidol-induced catalepsy was diminished by bilateral microinjections of 10 micrograms and 20 micrograms but not by 5 micrograms of DA in the PFC. The higher the dose of DA, the longer the decrease of catalepsy. These results suggest that an increase of DA turnover in the PFC might mediate temporal suppression of haloperidol-induced catalepsy. The mechanism by which the mesocortical DA system reduces catalepsy is discussed.

A study of the mechanism of MDMA ('ecstasy')-induced neurotoxicity of 5-HT neurones using chlormethiazole, dizocilpine and other protective compounds

1. An investigation has been made in rats into the neurotoxic effect of the relatively selective 5-hydroxytryptamine (5-HT) neurotoxin, 3,4-methylenedioxymethamphetamine (MDMA or 'Ecstasy') using chlormethiazole and dizocilpine, both known neuroprotective compounds and also gamma-butyrolactone, ondansetron and pentobarbitone. 2. Administration of MDMA (20 mg kg-1, i.p.) resulted in a 50% loss of cortical and hippocampal 5-HT and 5-hydroxyindole acetic acid (5-HIAA) 4 days later. This reflects the long term neurotoxic loss of 5-HT that occurs. Injection of gamma-butyrolactone (GBL; 400 mg kg-1, i.p.) 5 min before and 55 min after the MDMA provided substantial protection. Pentobarbitone (25 mg kg-1, i.p.) using the same dose regime was also protective, but ondansetron (0.5 mg kg-1 or 0.1 mg kg-1, i.p.) was without effect. 3. MDMA (20 mg kg-1) had no significant effect on striatal dopamine concentration 4 days later but did produce a small decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) content. There were few significant changes in rats given MDMA plus GBL, ondansetron or pentobarbitone. 4. A single injection of MDMA (20 mg kg-1, i.p.) resulted in a greater than 80% depletion of 5-HT in hippocampus and cortex 4 h later, reflecting the initial rapid release that had occurred. None of the neuroprotective compounds (chlormethiazole, 50 mg kg-1; dizocilpine, 1 mg kg-1; GBL, 400 mg kg-1; pentobarbitone, 25 mg kg-1) given 5 min before and 55 min after the MDMA injection, altered the degree of 5-HT loss. 5. Acute MDMA injection increased striatal dopamine content (28%) and decreased the DOPAC content. In general, administration of the drugs under investigation did not significantly alter these MDMA-induced changes. Both chlormethiazole and GBL produced a greater increase in dopamine than MDMA alone, but this was apparently an additive effect to the action of either drug alone. 6. The 5-HT loss 4 h following administration of the neurotoxin p-chloroamphetamine (2.5 mg kg-1,i.p.) was not affected by chlormethiazole or dizocilpine. p-Chloroamphetamine did not appear to alter striatal dopamine metabolism.7. None of the protective drugs inhibited the initial 5-HT loss following MDMA, rendering unlikely any proposal that they are protective because they inhibit 5-HT release and the subsequent formation ofa toxic indole derivative. All the protective compounds (unlike ondansetron) probably inhibit dopamine release in the striatum. Since the neurotoxic action of some substituted amphetamines is dependent on the integrity of nigro-striatal neurones, this fact may go some way to explain the protective action of this diverse group of compounds.

Anti-glutamatergic effects of clozapine

Clozapine (Cz) is unique in its efficacy with treatment refractory patients and its freedom from motor side effects. The present work shows that Cz, even after dopamine depletion, suppresses responses evoked via the monosynaptic glutamatergic corticostriatal pathway. In addition, Cz is effective in displacing [3H]MK-801 from striatal homogenates. These data indicate that Cz is a glutamate antagonist. It is unclear, however, if this pharmacological action could explain Cz's lack of motor effects and it's antipsychotic potency.

The non-NMDA glutamate receptor antagonist GYKI 52466 counteracts locomotor stimulation and anticataleptic activity induced by the NMDA antagonist dizocilpine

The effects of the non-NMDA glutamate receptor antagonist GYKI 52466 (2.4 and 4.8 mg/kg, i.p.) on spontaneous locomotor activity and haloperidol-induced catalepsy (0.5 mg/kg, i.p.) were assessed in naive rats and in rats pretreated with the NMDA antagonist dizocilpine (0.08 mg/kg, i.p.). GYKI 52466 given alone did not alter locomotor activity and haloperidol-induced catalepsy, but significantly antagonized the dizocilpine-induced locomotor stimulation and counteracted the anti-cataleptic effects of dizocilpine on haloperidol-induced catalepsy. Thus blockade of non-NMDA glutamate receptors antagonized the behavioural stimulant effects of a NMDA receptor blockade.

Clozapine improves dizocilpine-induced delayed alteration impairment in rats

The effects of systemic administration of dizocilpine (0.16 mg/kg, i.p.), clozapine (7.5 mg/kg, s.c.) and coadministration of dizocilpine (0.16 mg/kg, i.p.) and clozapine (7.5 mg/kg, s.c.) on acquisition of delayed alternation in a T-maze were tested in rats (N = 7 per group) on six days with 10 choices per day and animal. Clozapine given alone did not impair delayed alternation learning, except of the first day. Dizocilpine induced a significant delayed alternation impairment on all days tested. Pretreatment with clozapine significantly improved the dizocilpine-induced impairment. Treatment-induced changes of delayed alternation learning and of locomotor activities showed no correlation. The results demonstrate that clozapine functionally compensated for deficits induced by a blockade of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors.

NMDA receptor antagonists inhibit catalepsy induced by either dopamine D1 or D2 receptor antagonists

In the present study, we investigated the ability of NMDA receptor antagonists to inhibit catalepsy induced by haloperidol, or SCH23390 and clebopride, selective dopamine D1 and D2 receptor antagonists respectively. Catalepsy was measured by recording the time the animal remained with its forepaws placed over a rod 6 cm above the bench. Pretreatment with either the non-competitive NMDA receptor antagonist, MK-801 (0.25-0.5 mg/kg i.p.) or the competitive antagonist, LY274614 (10-20 mg/kg i.p.) reduced the cataleptic response produced by haloperidol (10 mg/kg), SCH23390 (2.5-10 mg/kp i.p.) or clebopride (5-20 mg/kg i.p.). This demonstrates that NMDA receptor antagonists will reduce both dopamine D1 and D2 receptor antagonist-induced catalepsy. Muscle relaxant doses of chlordiazepoxide (10 mg/kg i.p.) failed to reduce the catalepsy induced by haloperidol, suggesting that the anticataleptic effect of the NMDA receptor antagonists was not due to a non-specific action. These results support the hypothesis that NMDA receptor antagonists may have beneficial effects in disorders involving reduced dopaminergic function, such as Parkinson's disease.

Discrete quinolinic acid lesions of the lateral but not of the medial caudate-putamen reversed haloperidol-induced catalepsy in rats

Discrete lesions in the medial or lateral subregion of the rostral caudate-putamen (CP) were induced by bilateral intracerebral injections of a low dose of quinolinic acid (30 nmol in 1 microliter/per side) in rats. Quinolinic acid lesions in the lateral CP potently reversed haloperidol-induced catalepsy (0.5 mg/kg,i.p.), while lesions in the medial CP were not effective. Spontaneous locomotor activity was not altered significantly after quinolinic acid lesions of either the medial or lateral CP. These results show that the lateral CP seems to be important for the expression of neuroleptic-induced catalepsy and thus further corroborate the concept of a functional heterogeneity of the striatum.