Clozapine and sulpiride up-regulate dopamine D3 receptor mRNA levels

Understanding the Therapeutic Action of Antipsychotics: From Molecular to Cellular Targets With Focus on the Islands of Calleja

The understanding of the pathophysiology of schizophrenia as well as the mechanisms of action of antipsychotic drugs remains a challenge for psychiatry. The demonstration of the therapeutic efficacy of several new atypical drugs targeting multiple different receptors, apart from the classical dopamine D2 receptor as initially postulated unique antipsychotic target, complicated even more conceptualization efforts. Here we discuss results suggesting a main role of the islands of Calleja, still poorly studied GABAergic granule cell clusters in the ventral striatum, as cellular targets of several innovative atypical antipsychotics (clozapine, cariprazine, and xanomeline/emraclidine) effective in treating also negative symptoms of schizophrenia. We will emphasize the potential role of dopamine D3 and M4 muscarinic acetylcholine receptor expressed at the highest level by the islands of Calleja, as well as their involvement in schizophrenia-associated neurocircuitries. Finally, we will discuss the implications of new data showing ongoing adult neurogenesis of the islands of Calleja as a very promising antipsychotic target linking long-life neurodevelopment and dopaminergic dysfunction in the striatum.

Clozapine's multiple cellular mechanisms: What do we know after more than fifty years? A systematic review and critical assessment of translational mechanisms relevant for innovative strategies in treatment-resistant schizophrenia

Almost fifty years after its first introduction into clinical care, clozapine remains the only evidence-based pharmacological option for treatment-resistant schizophrenia (TRS), which affects approximately 30% of patients with schizophrenia. Despite the long-time experience with clozapine, the specific mechanism of action (MOA) responsible for its superior efficacy among antipsychotics is still elusive, both at the receptor and intracellular signaling level. This systematic review is aimed at critically assessing the role and specific relevance of clozapine's multimodal actions, dissecting those mechanisms that under a translational perspective could shed light on molecular targets worth to be considered for further innovative antipsychotic development. In vivo and in vitro preclinical findings, supported by innovative techniques and methods, together with pharmacogenomic and in vivo functional studies, point to multiple and possibly overlapping MOAs. To better explore this crucial issue, the specific affinity for 5-HT₂R, D1R, α_2c, and muscarinic receptors, the relatively low occupancy at dopamine D2R, the interaction with receptor dimers, as well as the potential confounder effects resulting in biased ligand action, and lastly, the role of the moiety responsible for lipophilic and alkaline features of clozapine are highlighted. Finally, the role of transcription and protein changes at the synaptic level, and the possibility that clozapine can directly impact synaptic architecture are addressed. Although clozapine's exact MOAs that contribute to its unique efficacy and some of its severe adverse effects have not been fully understood, relevant information can be gleaned from recent mechanistic understandings that may help design much needed additional therapeutic strategies for TRS.

DRD3 Ser9Gly polymorphism and treatment response to antipsychotics in schizophrenia: A meta-analysis

The association between dopamine D3 receptor (DRD3) Ser9Gly polymorphism and treatment response to antipsychotic drugs (APDs) in schizophrenia (SCZ) has been widely reported with inconsistent results, thus we performed an updated meta-analysis to derive a more precise estimation of the relationship. PubMed, Cochrane Library, Medline, Embase, CNKI, Weipu and Wanfang databases were searched for eligible studies published until March 2022. Odds ratios (ORs) with 95 % confidence intervals (CIs) were used to assess the strength of the associations in four genetic models. A total of 13 studies with 1769 patients were included in this meta-analysis. Our findings suggested that Ser9Gly polymorphism was significantly associated with treatment response to APDs in SCZ in allele model (Ser vs Gly, OR = 0.72, 95 % CI = 0.58-0.89, P = 0.002), recessive model (Ser/Ser vs Ser/Gly + Gly/Gly, OR = 0.55, 95 % CI = 0.36-0.86, P = 0.008) and co-dominant model (Ser/Ser vs Gly/Gly, OR = 0.57, 95 % CI = 0.33-0.99, P = 0.045) in Caucasians, but not in Asians. meta-regression revealed that the associations were not confounded by mean age, male ratio and treatment duration (P > 0.05). In summary, our results indicated the DRD3 Ser9Gly may influence the efficacy of APDs in specific genetic models, of which Ser allele and Ser/Ser genotype contributed to poor treatment response in Caucasians.

Corticosterone and dopamine D2/D3 receptors mediate the motivation for voluntary wheel running in C57BL/6J mice

Physical exercise can improve cognition but whether this is related to motivation levels is unknown. Voluntary wheel running is a rewarding activity proposed as a model of motivation to exercise. To question the potential effects of exercise motivation on subsequent behaviour, we used a pharmacological approach targeting some reward mechanisms. The stress hormone corticosterone has rewarding effects mediated by activation of low affinity glucocorticoid receptors (GR). To investigate whether corticosterone synthesis motivates exercise via activation of GRs and subsequently, impacts on behaviour, we treated C57BL/6J mice acutely with the inhibitor of corticosterone synthesis metyrapone (35mg/kg) or repeatedly with the GR antagonist mifepristone (30mg/kg) prior to 1-h running wheel sessions. To investigate whether reducing motivation to exercise impacts on behaviour, we antagonised running-induced dopamine D2/D3 receptors activation with sulpiride (25 or 50mg/kg) and assessed locomotor, anxiety-related and memory performance after 20 running sessions over 4 weeks. We found that corticosterone synthesis contributes to running levels, but the maintenance of running behaviour was not mediated by activation of GRs. Intermittent exercise was not associated with changes in behavioural or cognitive performance. The persistent reduction in exercise levels triggered by sulpiride also had limited impact on behavioural performance, although the level of performance for some behaviours was related to the level of exercise. Altogether, these findings indicate that corticosterone and dopamine D2/D3 receptor activation contribute to the motivation for wheel running, but suggest that motivation for exercise is not a sufficient factor to alter behaviour in healthy mice.

Dopamine D3 receptors regulate GABAA receptor function through a phospho-dependent endocytosis mechanism in nucleus accumbens

The dopamine D3 receptor, which is highly enriched in nucleus accumbens (NAc), has been suggested to play an important role in reinforcement and reward. To understand the potential cellular mechanism underlying D3 receptor functions, we examined the effect of D3 receptor activation on GABAA receptor (GABAAR)-mediated current and inhibitory synaptic transmission in medium spiny neurons of NAc. Application of PD128907 [(4aR,10bR)-3,4a,4,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol hydrochloride], a specific D3 receptor agonist, caused a significant reduction of GABAAR current in acutely dissociated NAc neurons and miniature IPSC amplitude in NAc slices. This effect was blocked by dialysis with a dynamin inhibitory peptide, which prevents the clathrin/activator protein 2 (AP2)-mediated GABAA receptor endocytosis. In addition, the D3 effect on GABAAR current was prevented by agents that manipulate protein kinase A (PKA) activity. Infusion of a peptide derived from GABAAR beta subunits, which contains an atypical binding motif for the clathrin AP2 adaptor complex and the major PKA phosphorylation sites and binds with high affinity to AP2 only when dephosphorylated, diminished the D3 regulation of IPSC amplitude. The phosphorylated equivalent of the peptide was without effect. Moreover, PD128907 increased GABAAR internalization and reduced the surface expression of GABAA receptor beta subunits in NAc slices, which was prevented by dynamin inhibitory peptide or cAMP treatment. Together, our results suggest that D3 receptor activation suppresses the efficacy of inhibitory synaptic transmission in NAc by increasing the phospho-dependent endocytosis of GABAA receptors.

Dopamine D3 receptor and schizophrenia: A widened scope for the immune hypothesis

Schizophrenia may be related to immunity as is suggested by many findings of altered immune parameters in schizophrenic patients. How immune alterations might be involved in the emergence of psychosis is still unclear. Clearly, however, the dopamine hypothesis has been confirmed in recent studies, which implies a crucial role for dopamine and the dopamine D2 receptor (D2R) within the pathogenesis of schizophrenia. The Dopamine D3 receptor (D3R) is considered to have autoreceptor properties modulating the synthesis and release of dopamine, thereby possibly antagonizing the dopamine D2-receptor-mediated effects of dopamine and has been found reduced in schizophrenic patients during acute psychosis and increasing in the advent of negative schizophrenic symptoms. Immune parameters apparently influence the expression of dopamine receptors by means of their capability to induce regulatory factors involved in the expression of dopamine receptor subtypes, such as the neurotrophins, associations of which with psychosis have been reported repeatedly. Here, we propose a hypothesis of immune alterations that influence the production of distinct neurotrophins such as BDNF and NGF that, as animal studies suggest, influence the expression of dopamine receptor subtypes. This mechanism could result in a decrease of D3R and a consecutive relative preponderance of D2R and thereby connect immune alterations and schizophrenia.

Microarray analysis of differentially expressed genes in rat frontal cortex under chronic risperidone treatment

Long-term administration of antipsychotic drugs can induce differential expression of a variety of genes in the brain, which may underscore the molecular mechanism of the clinical efficacy and/or side effects of antipsychotic drugs. We used cDNA microarray analysis to screen differentially expressed genes in rat frontal cortex under 4 weeks' treatment of risperidone (1 mg/kg). Using real-time quantitative PCR, we were able to verify eight genes, whose expression were significantly upregulated in rat frontal cortex under chronic risperidone treatment when compared with control animals. These genes include receptor for activated protein kinase C, amida, cathepsin D, calpain 2, calcium-independent receptor for alpha-latrotoxin, monoamine oxidase B, polyubiquitin, and kinesin light chain. In view of the physiological function of these genes, the results of our study suggest that chronic risperidone treatment may affect the neurotransmission, synaptic plasticity, and proteolysis of brain cells. This study also demonstrates that cDNA microarray analysis is useful for uncovering genes that are regulated by chronic antipsychotic drugs treatment, which may help bring new insight into the molecular mechanism of antipsychotic drugs.

Association between dopamine D3 receptor gene polymorphisms and schizophrenia in an isolate population

There are several lines of evidence implicating the dopamine D3 receptor in the pathophysiology of schizophrenia. The Ser9Gly polymorphism of the dopamine D3 receptor gene (DRD3) has been the most extensively investigated DRD3 variant in connection with the disease but results have been inconclusive. Recent reports indicate that the Ser9Gly polymorphism is in linkage disequilibrium with other markers, but association studies between DRD3 haplotypes and schizophrenia have had mixed results. Genetic heterogeneity may be one of the causes of contradicting results. In order to clarify the role of DRD3 alterations in the aetiology of disease, we have investigated three D3 genetic variants (Ser9Gly, -205-G/A, -7685-G/C) in a sample of patients with schizophrenia or schizoaffective disorder (N=118) and controls (N=162) recruited from a human isolate from Navarra (Northern Spain) of Basque origin. Although no association was found between the Ser9Gly or the -205-A/G polymorphisms and disease, an excess of allele -7685-C was observed in patients (p=0.002 after correction for multiple analyses). Haplotype analysis shows the three markers to be in strong linkage disequilibrium (p<0.0001) and strongly associated with disease (p<1x 10(-5)). These results may suggest that these polymorphisms exert a combined or synergistic effect on susceptibility to schizophrenia, or are in linkage with an unknown causative factor. However, further replication in independent samples is required.

Gradient of dopamine responsiveness to dopamine receptor agonists in subregions of the rat nucleus accumbens

The present study sought to investigate the possibility that the degree of selectivity of dopamine D3/D2 receptor agonists such as quinelorane, 7-hydroxy-2-dipropylaminotetralin (7-OH-DPAT), quinpirole and apomorphine on dopamine D3 over D2 receptor subtypes can be assessed by measuring dopamine transmission in the shell vs. core compartments of the nucleus accumbens by using microdialysis in freely moving rats. Significant reductions in dialysate dopamine levels compared to vehicle-treated animals were observed in the shell of the nucleus accumbens with 3, 10 and 30 microg/kg quinelorane, 100 microg/kg 7-OH DPAT, 25 and 100 microg/kg quinpirole, and 100 microg/kg apomorphine. In the core subregion, significant reductions in dopamine were seen at 10 and 30 microg/kg quinelorane, 25 and 100 microg/kg 7-OH-DPAT, 100 microg/kg quinpirole and 100 microg/kg apomorphine. However, a significant shell/core dichotomy could only be observed in response to the lowest dose of quinelorane (3 microg/kg) with the shell being hyper-responsive compared with the core. The present findings suggest that quinelorane is one of the most selective dopamine D3 receptor agonists based on its ability to target the shell subregion of the nucleus accumbens.

Estudo de associação entre o polimorfismo serina-9-glicina do receptor dopaminérgico D3 e esquizofrenia

Duas abordagens genético-moleculares foram realizadas para investigar a possível associação entre o polimorfismo serina-9-glicina no receptor dopaminérgico D3 e esquizofrenia. Na primeira análise, um grupo de 141 pacientes com esquizofrenia foi comparado a um grupo-controle de 189 indivíduos pareado para sexo e origem étnica. No outro estudo, foi realizada análise de 35 trios (pai e mãe não afetados e paciente com esquizofrenia). Os resultados desses estudos não apresentaram associação alélica ou genotípica estatisticamente significante com esquizofrenia. Pode-se concluir que o polimorfismo serina-9-glicina no receptor dopaminérgico D3 não é um fator de risco para desenvolver esquizofrenia na população estudada.

Nigrostriatal dopaminergic denervation enhances dopamine D(4) receptor binding in rat caudate-putamen

Radioligand binding to dopamine (DA) D(4) receptors was examined in adult rat forebrain 5 weeks after unilateral 6-hydroxydopamine (6-OHDA) lesioning of substantia nigra to remove ascending nigrostriatal dopaminergic projections. D(4) receptor binding was increased by up to 47% in denervated caudate-putamen (CPu) in rats that rotated away from the lesioned side with apomorphine challenge, with lesser changes in rats that failed to rotate with apomorphine. Functional significance of D(4) receptor upregulation induced by the lesions was investigated by examining behavioral effects of the highly selective D(4) agonist CP-226,269 and antagonist CP-293,019. Neither agent induced rotation at doses as high as 30 mg/kg ip. Pretreatment with the D(4) antagonist CP-293,019 did not affect rotation induced by either a D(1)-like (SKF-38393) or D(2)-like receptor (quinpirole) agonist. These findings provide the first evidence that D(4) receptors can be upregulated by nigrostriatal dopaminergic denervation. They also suggest that, unlike D(1) and D(2) receptors, D(4) receptors do not play a pivotal role in rotational behavior in rats with unilateral dopaminergic lesions.

Dopamine D3 receptor gene polymorphism and response to clozapine in schizophrenic Pakastani patients

The dopamine D3 receptor (DRD3) appears to play an important role in the mediation of antipsychotic drug action. Genetic association of treatment response to the atypical antipsychotic drug clozapine with the DRD3 polymorphism Ser9Gly was investigated in a sample of 32 schizophrenic patients. We found association of treatment response with allele Gly-9 (P=0.0058) and with genotypes consisting of Gly-9 (P=0.033) by this pharmacogenetic approach. A combined analysis with two previous studies (Shaikh et al., Hum. Genet. 97 (1996) 714-719; Malhotra et al., Mol. Psychiatry 3 (1998) 72-75) further substantiates these results (P=0.0041).

Effects of haloperidol on the expression of lymphocyte dopamine receptor mRNAs in the rat

1. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to investigate the effects of haloperidol treatment (1 mg/kg/day for 2, 7 or 21 consecutive days) on the expression of D1B and D3 dopamine receptor mRNAs in the rat lymphocytes. 2. The expression of D1B receptor mRNA was significantly decreased after 2 days of treatment and progressively returned toward basal values at the end of treatment. Conversely, haloperidol failed to modify the expression of lymphocyte D3 receptor mRNA. 3. These results indicate short-lasting dynamic changes of expression of lymphocyte D1B dopamine receptor mRNA by haloperidol and suggest that the effects of dopamine and dopaminergic drugs on the immune system might be mediated, at least in part, by direct interaction of these substances with dopamine receptors on lymphocyte membrane.

Antipsychotic regulation of dopamine D1, D2 and D3 receptor mRNA

A range of antipsychotic drugs, both "typical" and "atypical", was administered to rats over a time course and at several different dosages. The mRNA levels of dopamine D1, D2 and D3 receptor were measured in either whole brain or dissected brain regions. D3 receptor mRNA was up-regulated in whole brain by clozapine (10 and 30 but not 3 mg/kg/day), sulpiride (50 and 100 but not 20 mg/kg/day). haloperidol (3 but not 1 or 0.3 mg/kg/day), flupenthixol (3 but not 1 or 0.3 mg/kg/day), pimozide (4.5 but not 1.5 or 0.5 mg/kg/day) and loxapine (1.2 and 4 mg/kg/day but not 0.4 mg/kg/day). Sulpiride (100 mg/kg/day), clozapine (30 mg/kg/ day) and haloperidol (3 mg/kg/day) all up-regulated the D3 receptor mRNA in nucleus accumbens and olfactory tubercles but not striatum. D1 and D2 receptor mRNA was up-regulated in whole brain by haloperidol and loxapine only, and in the case of haloperidol this was localized to striatum and prefrontal cortex. Haloperidol, clozapine and sulpiride all down-regulated D1 mRNA in hippocampus and additionally haloperidol and sulpiride down-regulated it in the cerebellum. This work shows that all the drugs tested up-regulated D3 receptor, but effects on D1 and D2 receptors were less general.

The effects of antipsychotic drugs on the mRNA levels of serotonin 5HT2A and 5HT2C receptors

We have looked for both global and regional changes in rat brain mRNA levels encoding serotonin 5HT2A and 5HT2C receptors following acute and chronic administration of antipsychotic drugs. In whole brain clozapine (30 mg/kg/day) elicited a transient rise in 5HT2C mRNA levels after 4 days and chlorpromazine (15 mg/kg/day) elicited a decrease of 20% in 5HT2A mRNA levels after 32 days. Regionally, 32 days treatment with haloperidol (3 mg/kg/day), sulpiride (100 mg/kg/day) or clozapine (10 mg/kg/day) resulted in a drop of approximately 30-40% in 5HT2C mRNA levels in both cortex and cerebellum, and decreases (or non-significant trends) of 15-40% in 5HT2A mRNA levels in hippocampus, brainstem and mid brain. 4 days treatment with clozapine resulted in a 40% rise of 5HT2C mRNA in the mid brain and a 24% rise of 5HT2A mRNA in the nucleus accumbens which were not found after 32 days of treatment. These results demonstrate common chronic effects of typical and atypical drugs but unique short term effects of clozapine.

Aripiprazole, a novel antipsychotic drug, inhibits quinpirole-evoked GTPase activity but does not up-regulate dopamine D2 receptor following repeated treatment in the rat striatum

Aripiprazole, a quinolinone derivative, is a new dopaminergic agent which has been recently developed and demonstrated to be clinically useful as an antipsychotic drug with reduced extrapyramidal motor side effects. Here, we found that aripiprazole competed [3H]spiperone binding with a 100-fold higher affinity than [3H]SCH23390 binding, and inhibited the quinpirole-induced facilitation of high-affinity GTPase activity in rat striatal membranes. The effects of chronic administration of aripiprazole and haloperidol on dopamine D2 receptor binding and mRNA level in rat striata were examined by a [3H]spiperone binding assay and a ribonuclease protection assay. Haloperidol induced a significant rise in Bmax of [3H]spiperone binding at 1 mg/kg and in the level of dopamine D2L receptor mRNA at 4 mg/kg. A high dose of aripiprazole (100 mg/kg) only tended to increase the Bmax of [3H]spiperone binding non-significantly, and had no effect on the level of dopamine D2L receptor mRNA. These results indicated that aripiprazole had an antagonistic activity to dopamine D2 receptors with a high affinity, but that the potency of aripiprazole to up-regulate dopamine D2 receptors in the striatum was much smaller than that of haloperidol. This small up-regulation may be related to the ability to aripiprazole to act without side effects including tardive dyskinesia.

Homozygosity at the dopamine D3 receptor gene in schizophrenic patients

Dopamine receptors have long been implicated in the etiology of schizophrenia. It has been reported an association of schizophrenia with homozygosity at the dopamine D3 receptor gene locus. We have investigated the distribution of a D3 receptor gene polymorphism (BalI) in 107 schizophrenic Spanish patients and 100 healthy matched controls. No statistically significant differences between the patients and control group were detected with respect to either allele frequencies or genotype distribution. However, if not corrected for multiple testing, a correlation was found between homozygosity and early age of onset of schizophrenia (chi 2 = 3.1, df = 1, P = 0.03) and between A1 allele frequency and disorganized and undifferentiated schizophrenia (chi 2 = 3.4, df = 1, P = 0.03; chi 2 = 2.7, df = 1, P = 0.05, respectively). These results suggest the possibility that D3 polymorphisms may be among the physiological factors underlying schizophrenia; though not the determining factor.

The molecular genetics of schizophrenia

There is overwhelming evidence for a significant genetic contribution to the etiology of schizophrenia. Molecular genetic techniques are now sufficiently advanced to be applied to complex genetic disorders with uncertain phenotypes, such as schizophrenia. In this article we first briefly discuss certain pertinent background issues: the evidence that schizophrenia has a heritable basis, the possible modes of inheritance involved, and how best to define schizophrenia in the light of this evidence; we then review the current status of research in the field. Large collaborative studies are currently underway that pave the way for the detection of genes of both major and minor effects. We may now be seeing the first consistently replicated results from chromosome 6 and 22 and from candidate genes, such as the dopamine D3 receptor gene.

Allelic association between a Ser-9-Gly polymorphism in the dopamine D3 receptor gene and schizophrenia

We examined a Ser-9-Gly polymorphism in the dopamine D3 receptor gene for allelic association with schizophrenia in 133 patients currently treated with clozapine and 109 controls. Allele 1 (Ser-9) was significantly more frequent in the patients (69%) than in the controls (56%) (P = 0.004). The 1-1 genotype was more common (43% vs 30%) and the 2-2 genotype less common (5% vs 18%) in patients than in controls. When the patient group was subdivided on the basis of clinical response to clozapine, using a 20-point improvement in the global assessment scale as cut-off, genotype 1-1 was found to be more frequent among the non-responders (53% vs 36%, P = 0.04). To place our results in the context of previous studies of this polymorphism and schizophrenia, we performed a meta-analysis of all published data including the present sample. The combined analysis shows evidence for a modest association between genotype 1-1 and schizophrenia (odds ratio 1.25, 95% confidence interval 1.05-1.49, P = 0.01). These results suggest that the Ser-9 allele, or a nearby polymorphism in linkage disequilibrium, results in a small increase in susceptibility to schizophrenia.

Mechanisms of action of atypical antipsychotic drugs: a critical analysis

Various criteria used to define atypical antipsychotic drugs include: 1) decrease, or absence, of the capacity to cause acute extrapyramidal motor side effects (acute EPSE) and tardive dyskinesia (TD); 2) increased therapeutic efficacy reflected by improvement in positive, negative, or cognitive symptoms; 3) and a decrease, or absence, of the capacity to increase prolactin levels. The pharmacologic basis of atypical antipsychotic drug activity has been the target of intensive study since the significance of clozapine was first appreciated. Three notions have been utilized conceptually to explain the distinction between atypical versus typical antipsychotic drugs: 1) dose-response separation between particular pharmacologic functions; 2) anatomic specificity of particular pharmacologic activities; 3) neurotransmitter receptor interactions and pharmacodynamics. These conceptual bases are not mutually exclusive, and the demonstration of limbic versus extrapyramidal motor functional selectivity is apparent within each arbitrary theoretical base. This review discusses salient distinctions predominantly between prototypic atypical and typical antipsychotic drugs such as clozapine and haloperidol, respectively. In addition, areas of common function between atypical and typical antipsychotic drug action may also be crucial to our identification of pathophysiological foci of the different dimensions of schizophrenia, including positive symptoms, negative symptoms, and neurocognitive deficits.

Relapse following clozapine withdrawal: effect of neuroleptic drugs and cyproheptadine

The objective of this study was to report the effect of the slow withdrawal of clozapine from 19 patients with neuroleptic-responsive schizophrenia at the end of a 2-year clinical trial of clozapine and to compare this with the results of naturalistic discontinuation of clozapine treatment in 64 neuroleptic-resistant schizophrenic patients. Nineteen neuroleptic-responsive schizophrenic patients who received clozapine were withdrawn from clozapine by tapering it over 3-week period with and without the addition of a typical neuroleptic. Fifteen of the 19 neuroleptic-responsive patients experienced the return of psychotic symptoms during or after the clozapine taper, which were most severe in the ten patients in whom the withdrawal of clozapine was carried out without prior addition of neuroleptic treatment. Addition of a neuroleptic prior to clozapine withdrawal prevented the emergence of positive symptoms during clozapine withdrawal in each of eight patients. Nevertheless, psychotic symptoms emerged, usually within a week after discontinuing clozapine, in six of the eight patients. Neuroleptic treatment, with or without an anticholingergic drug, was much less effective in treating positive symptoms in these patients immediately after the clozapine withdrawal than it had been 2 years previously. Cyproheptadine, a non-selective serotonin receptor antagonist, augmented the antipsychotic effect of neuroleptics in each of four patients who relapsed following withdrawal from clozapine and relieved extrapyramidal symptoms in a fifth patient. The frequency of relapse following withdrawal of clozapine in 64 neuroleptic-resistant patients was significantly lower (25/64, 39.1%) than in the neuroleptic-responsive patients.

Amphetamine and vigabatrin down regulate aromatic L-amino acid decarboxylase mRNA levels

Aromatic L-amino acid decarboxylase (AADC) has previously been shown to be up-regulated at the level of its protein activity and its mRNA abundance by antipsychotic drugs. Its activity has also been shown to be down-regulated by dopamine agonists including amphetamine. In this study we have injected rats for up to 32 days with amphetamine and the anti-epileptic drug vigabatrin, both of which can cause psychosis with similarities to schizophrenia. We have shown that AADC mRNA levels are reduced in most brain regions by both drugs. Cocaine and other non-psychotogenic anti-epileptic drugs had no effect in this paradigm. Two products of this enzyme are implicated in psychotogenesis.

A paradoxical regulation of the dopamine D3 receptor expression suggests the involvement of an anterograde factor from dopamine neurons

The effects of interruption of dopaminergic transmission or sustained blockade of dopamine receptors by neuroleptics on the dopamine D3 receptor in the shell of the nucleus accumbens were investigated in rats. In this brain area the D3 receptor is abundant and may mediate antipsychotic drug effects. The D3 receptor density and mRNA abundance were evaluated with 7-[3H]hydroxy-N,N-di-n-propyl-2-aminotetralin and by quantitative PCR or image analysis of in situ hybridization signals, respectively. Unilateral dopamine neuron degeneration by 6-hydroxydopamine or sections triggered, after a few days, a marked decrease (up to 50%) in D3 receptor binding and mRNA in the nucleus accumbens. In contrast, a 2-week treatment with the neuroleptic haloperidol (20 mg/kg) had no effect on D3 receptor density and mRNA but enhanced D2 receptor density and mRNA level by > 50%. In addition, tolerance to the haloperidol-induced change of neurotensin mRNA mediated by the D2 receptor developed, but there was no tolerance to the opposite change mediated by the D3 receptor. Reserpine, a monoamine-depleting drug with antipsychotic activity, did not modify D3 receptor mRNA. These observations reinforce the idea that the D3 receptor may be an important target for neuroleptics whose antipsychotic actions, but not extrapyramidal motor actions, do not display tolerance. The D3 receptor mRNA level was also decreased by a unilateral injection in dopamine cell body areas of colchicine, a drug blocking the anterograde axonal transport, or by baclofen, a type A gamma-aminobutyric acid receptor agonist reducing dopamine neuron activity, but not by sustained blockade of D1-like and D2-like, neurotensin, or cholecystokinin receptors. We therefore propose that an anterograde factor present in mesolimbic dopaminergic neurons, but distinct from dopamine and known peptide cotransmitters, plays a positive role on transcription of the D3 receptor gene.

Differential changes in glutamate receptor subunit messenger RNAs in rat brain after haloperidol treatment

Glutamate receptors are implicated in several neuropsychiatric disorders and in the actions of neuroleptic drugs used to treat them. To help clarify how these drugs impinge upon the glutamatergic system, we have studied the effects of 2 weeks' haloperidol (2 mg kg(-1) d(-1)) upon the distribution and abundance of glutamate receptor mRNAs in rat brain. The mRNAs detected were those encoding the glutamate-binding protein (GBP), the N-methyl D-aspartate (NMDA) receptor (NR1 subunit) and the flip and flop isoforms of α-amino-3-hydroxy- 5-methyl-4-isoxazolpropionate (AMPA)-preferring non-NMDA receptors gluR1 and gluR2. The mRNAs were studied using in situ hybridization histochemistry in dorsolateral striatum, nucleus accumbens, frontal cortex and hippocampus. Haloperidol led to an increase in GBP mRNA in striatum and frontal cortex but not in hippocampus. AMPA receptor mRNAs showed gene- and isoform-specific alterations in treated animals, with a significant increase in the proportion of gluR2 flip compared to gluR2 flop. The gluR1 flop:gluR2 flop ratio also increased. No differences were observed for NR1 mRNA in any area. Thus, subchronic administration of haloperidol has a molecularly and spatially specific effect upon expression of glutamate receptor-related transcripts. The data have several implications. Firstly, the enhanced expression of GBP mRNA may contribute to the alterations in other glutamatergic parameters observed after neuroleptics. Secondly, the pattern of changes for the NMDA and AMPA receptor mRNAs suggests that the alterations in density of these receptors and their mRNAs reported in schizophrenia are not an artefact of neuroleptic treatment. Finally, the specific increase in flip:flop mRNA ratio for gluR2, together with the increased proportion of gluR1 flop:gluR2 flop mRNA, is likely to affect the properties of the encoded AMPA receptors. Such changes may be relevant to the desired or undesired effects of these drugs.