Neuroleptic-induced vacuous chewing movements as an animal model of tardive dyskinesia: a study in three rat strains

Gaba transporter SLC6A11 gene polymorphism associated with tardive dyskinesia

BACKGROUND

Gamma-aminobutyric acid (GABA) insufficiency has been reported to be related to the tardive dyskinesia (TD) susceptibility. Inada et al. (Pharmacogenet Genomics 2008;18:317-23) identified eight genes belonging to GABA receptor signaling pathway that may be involved in TD susceptibility by genome-wide screening and they replicated associations in an independent sample for polymorphisms in SLC6A11 (GABA transporter 3), GABRG3 (c-3 subunit of GABA-A receptor) and GABRB2 (β-2 subunit of GABA-A receptor). In this study, we tried to replicate their finding in a larger Korean sample and find if any of the genes was associated with the susceptibility to TD.

METHODS

We selected three polymorphisms in SLC6A11 (rs4684742), GABRG3 (rs2061051) and GABRB2 (rs918528) from the previous study. We carried out a case-control study (105 TD and 175 non-TD schizophrenic patients) to identify the association between the three candidate polymorphisms and susceptibility to TD and their epistatic interactions by using the multifactor dimensionality reduction (MDR) algorithm.

RESULTS

Among the three variants, SCL6A11 genotypes distribution showed a significant difference between the TD and non-TD patients (P = 0.049). However, GABRG3 and GABRB2 genotype distributions were not associated with TD (P = 0.268 and P = 0.976, respectively). Further, our analyses provided significant evidence for gene-gene interactions (SCL6A11, GABRG3 and GABRB2) in the development of TD. The odds ratio increased to 2.53 (CI = 1.515-4.217, P = 0.0003) when the genetic susceptibility to TD was analyzed with the three genes considered altogether through MDR approach.

CONCLUSION

These results suggest that GABA receptor signaling pathway was associated with the increased susceptibility to TD in Korean schizophrenic patients.

Postmortem brain: an underutilized substrate for studying severe mental illness

We propose that postmortem tissue is an underutilized substrate that may be used to translate genetic and/or preclinical studies, particularly for neuropsychiatric illnesses with complex etiologies. Postmortem brain tissues from subjects with schizophrenia have been extensively studied, and thus serve as a useful vehicle for illustrating the challenges associated with this biological substrate. Schizophrenia is likely caused by a combination of genetic risk and environmental factors that combine to create a disease phenotype that is typically not apparent until late adolescence. The complexity of this illness creates challenges for hypothesis testing aimed at understanding the pathophysiology of the illness, as postmortem brain tissues collected from individuals with schizophrenia reflect neuroplastic changes from a lifetime of severe mental illness, as well as treatment with antipsychotic medications. While there are significant challenges with studying postmortem brain, such as the postmortem interval, it confers a translational element that is difficult to recapitulate in animal models. On the other hand, data derived from animal models typically provide specific mechanistic and behavioral measures that cannot be generated using human subjects. Convergence of these two approaches has led to important insights for understanding molecular deficits and their causes in this illness. In this review, we discuss the problem of schizophrenia, review the common challenges related to postmortem studies, discuss the application of biochemical approaches to this substrate, and present examples of postmortem schizophrenia studies that illustrate the role of the postmortem approach for generating important new leads for understanding the pathophysiology of severe mental illness.

Oxidative stress and tardive dyskinesia: pharmacogenetic evidence

Tardive dyskinesia (TD) is a serious adverse effect of long-term antipsychotic use. Because of genetic susceptibility for developing TD and because it is difficult to predict and prevent its development prior to or during the early stages of medication, pharmacogenetic research of TD is important. Additionally, these studies enhance our knowledge of the genetic mechanisms underlying abnormal dyskinetic movements, such as Parkinson's disease. However, the pathophysiology of TD remains unclear. The oxidative stress hypothesis of TD is one of the possible pathophysiologic models for TD. Preclinical and clinical studies of the oxidative stress hypothesis of TD indicate that neurotoxic free radical production is likely a consequence of antipsychotic medication and is related to the occurrence of TD. Several studies on TD have focused on examining the genes involved in oxidative stress. Among them, manganese superoxide dismutase gene Ala-9Val polymorphisms show a relatively consistent association with TD susceptibility, although not all studies support this. Numerous pharmacogenetic studies have found a positive relationship between TD and oxidative stress based on genes involved in the antioxidant defense mechanism, dopamine turnover and metabolism, and other antioxidants such as estrogen and melatonin. However, many of the positive findings have not been replicated. We expect that more research will be needed to address these issues.

There is no evidence for an association between the serotonin receptor 3A gene C178T polymorphism and tardive dyskinesia in Korean schizophrenia patients

BACKGROUND

Tardive dyskinesia (TD) is a potential adverse effect of long-term treatment with antipsychotics. Previous studies have suggested a link between brain serotonergic systems and TD vulnerability. A recent report described that a serotonin 3 receptor (5-HTR3) agonist induced rhythmic movements in mice with complete paraplegia. Furthermore, it has been reported that the 5-HTR3 antagonist ondansetron is efficacious in the treatment of Gilles de la Tourette syndrome (GTS).

AIM

The aim of the present study was to determine whether the 5-HTR3A gene C178T polymorphism is associated with antipsychotic-induced TD in Korean schizophrenia patients.

METHODS

We investigated 280 Korean schizophrenia patients. Subjects with TD (n = 105) and without TD (n = 175) were matched for antipsychotic drug exposure and other relevant variables.

RESULTS

The distributions of genotypic (chi-squared = 3.55, p = 0.169) and allelic (chi-squared = 0.40, p = 0.528) frequencies did not differ between patients with and without TD. The total score on the Abnormal Involuntary Movement Scale also did not differ between the two genotype groups (F = 0.94, p = 0.391).

CONCLUSIONS

The findings of the present study do not support the involvement of the 5-HTR3A gene C178T polymorphism in TD in Korean schizophrenia subjects.

Early gene mapping after deep brain stimulation in a rat model of tardive dyskinesia: comparison with transient local inactivation

Deep brain stimulation (DBS) has been extensively used in Parkinson's disease and is also currently being investigated in tardive dyskinesia (TD), a movement disorder induced by chronic treatment with antipsychotic drugs such as haloperidol (HAL). In rodents, vacuous chewing movements (VCMs) following chronic HAL administration are suggested to model orofacial dyskinesias in TD. We show that 60 min of DBS (100 μA, 90 μs, 130 Hz) applied to the entopeduncular (EPN) or subthalamic (STN) nuclei significantly decreases HAL-induced VCMs. Using zif268 as a neural activity marker, we found that in HAL-treated animals EPN stimulation increased zif268 mRNA levels in the globus pallidus (+65%) and substantia nigra compacta (+62%) and reticulata (+76%), while decreasing levels in the motor cortex and throughout the thalamus. In contrast, after STN DBS zif268 levels in HAL-treated animals decreased in all basal ganglia structures, thalamus and motor cortex (range: 29% in the ventrolateral caudate-putamen to 100% in the EPN). Local tissue inactivation by muscimol injections into the STN or EPN also reduced VCMs, but to a lesser degree than DBS. When applied to the EPN muscimol decreased zif268 levels in substantia nigra (-29%), whereas STN infusions did not result in significant zif268 changes in any brain area. These results confirm the effectiveness of DBS in reducing VCMs and suggest that tissue inactivation does not fully account for DBS effects in this preparation. The divergent effects of STN vs. EPN manipulations on HAL-induced zif268 changes suggest that similar behavioral outcomes of DBS in these two areas may involve different neuroanatomical mechanisms.

Parallels between behavioral and neurochemical variability in the rat vacuous chewing movement model of tardive dyskinesia

The widely accepted rat vacuous chewing movement model for tardive dyskinesia could be more fully mined through greater focus on individual variability in vulnerability to this neuroleptic-induced behavior. We have examined parallels between behavioral and neurobiological variability within a cohort in order to evaluate the role that neurobiological factors might play in determining susceptibility to tardive dyskinesia. Inter-observer reliability and individual consistency across time, in both spontaneous and neuroleptic-induced vacuous chewing movements, were empirically demonstrated. While this behavior increased across 8 months of observation in both vehicle controls and haloperidol-treated rats, pre-treatment baselines were predictive of final levels across individuals only in the vehicle control group, not the haloperidol-treated group. Haloperidol-induced elevations in neostriatal D2 and GAD(67) mRNA were not correlated with individual variability in haloperidol-induced vacuous chewing movements. Ambient noise during the observations was found to exacerbate chronic haloperidol-induced, but not spontaneous vacuous chewing movements. Significant correlations were found among the haloperidol-treated rats between nigral and tegmental GAD(67) and tegmental α7 mRNA levels, measured by in situ hybridization histochemistry, and vacuous chewing movements, specifically in the noisy conditions. Variability in these secondary responses to primary striatal dopamine and GABA perturbations may play a role in determining vulnerability to vacuous chewing movements, and by analogy, tardive dyskinesia. Both the differential predictive value of baseline vacuous chewing movements and the differential effect of noise, between controls and haloperidol-treated rats, add to evidence that haloperidol-induced vacuous chewing movements are regulated, in part, by different mechanisms than those mediating spontaneous vacuous chewing movements.

Relevance of animal models to human tardive dyskinesia

Tardive dyskinesia remains an elusive and significant clinical entity that can possibly be understood via experimentation with animal models. We conducted a literature review on tardive dyskinesia modeling. Subchronic antipsychotic drug exposure is a standard approach to model tardive dyskinesia in rodents. Vacuous chewing movements constitute the most common pattern of expression of purposeless oral movements and represent an impermanent response, with individual and strain susceptibility differences. Transgenic mice are also used to address the contribution of adaptive and maladaptive signals induced during antipsychotic drug exposure. An emphasis on non-human primate modeling is proposed, and past experimental observations reviewed in various monkey species. Rodent and primate models are complementary, but the non-human primate model appears more convincingly similar to the human condition and better suited to address therapeutic issues against tardive dyskinesia.

Deep brain stimulation of the subthalamic or entopeduncular nucleus attenuates vacuous chewing movements in a rodent model of tardive dyskinesia

Deep brain stimulation (DBS) has recently emerged as a potential intervention for treatment-resistant tardive dyskinesia (TD). Despite promising case reports, no consensus exists as yet regarding optimal stimulation parameters or neuroanatomical target for DBS in TD. Here we report the use of DBS in an animal model of TD. We applied DBS (100 μA) acutely to the entopeduncular nucleus (EPN) or subthalamic nucleus (STN) in rats with well established vacuous chewing movements (VCMs) induced by 12 weeks of haloperidol (HAL) treatment. Stimulation of the STN or EPN resulted in significant reductions in VCM counts at frequencies of 30, 60 or 130 Hz. In the STN DBS groups, effects were significantly more pronounced at 130 Hz than at lower frequencies, whereas at the EPN the three frequencies were equipotent. Unilateral stimulation at 130 Hz was also effective when applied to either nucleus. These results suggest that stimulation of either the EPN or STN significantly alleviates oral dyskinesias induced by chronic HAL. The chronic HAL VCM model preparation may be useful to explore mechanisms underlying DBS effects in drug-induced dyskinesias.

No Evidence for an Association between Dopamine D2 Receptor Polymorphisms and Tardive Dyskinesia in Korean Schizophrenia Patients

OBJECTIVE

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotic. Dopaminergic activity in the nigrostriatal system have been proposed to be involved in development of TD and dopamine D2 receptors (DRD2) has been regarded as a candidate gene for TD because the antipsychotics have potent antagonism DRD2. This study was aimed to find the relationship between DRD2 gene and antipsychotic-induced TD.

METHODS

We evaluated whether 5 DRD2 single nucleotide polymorphisms (-141Cins>del/TaqID/NcoI/Ser311Cys/TaqIA) are associated with antipsychotic-induced TD in 263 Korean schizophrenia patients with (n=100) and without TD (n=163) who were matched for antipsychotic drug exposure and other relevant variables. Haplotype analyses were also performed.

RESULTS

None of 5 polymorphisms were found to be significantly associated with TD and with TD severity as measured by Abnormal Involuntary Movement Scale. Overall haplotype (-141Cins>del/TaqID/NcoI/Ser311Cys/TaqIA) frequency was also not significantly different between TD and non-TD groups, although one rare haplotype (I-D1-T-G-A1) showed significantly different frequency between TD and non-TD groups (2.7% vs. 8.5%, respectively, p=0.031).

CONCLUSION

The present study does not support that DRD2 gene may be involved in TD in the Korean population, although further studies are warranted.

Novel approaches to the study of postmortem brain in psychiatric illness: old limitations and new challenges

Biological psychiatry has made significant advances through the development of postmortem studies, animal models, and studies with living humans. Although these approaches each have advantages and disadvantages, the postmortem field is undergoing a significant shift toward more complex and informative methodologies. In the first part of this review, we summarize the long-standing methodologic challenges facing this field. In the second part of the article, we discuss the innovative approaches being used for postmortem studies, including laser capture microdissection and subcellular fractionization. These techniques will permit scientists working in the postmortem field to ask and answer the largest possible questions, providing new targets for drug discovery and improved treatments for severe mental illness.

Genetics of tardive dyskinesia

Tardive dyskinesia (TD) is one of the most serious adverse side effects of antipsychotic drugs and is an important topic of pharmacogenetic studies. Since there is a genetic susceptibility for developing this adverse reaction, and given that it is hard to predict its development prior to or during the early period of medication, the genetic study of TD is a promising research topic that has a direct clinical application. Moreover, such studies would improve our understanding of the genetic mechanism(s) underlying abnormal dyskinetic movement. A substantial number of case-control association studies of TD have been performed, with numbers of studies focusing on the genes involved in antipsychotic drug metabolism, such as those for cytochrome P450 (CYP) and oxidative stress related genes as well as various neurotransmitter related genes. These studies have produced relatively consistent though controversial findings for certain polymorphisms such as CYP2D6*10, DRD2 Taq1A, DRD3 Ser9Gly, HTR2A T102C, and MnSOD Ala9Val. Moreover, the application of the genome-wide association study (GWAS) to the susceptibility of TD has revealed certain associated genes that previously were never considered to be associated with TD, such as the rs7669317 on 4q24, GLI2 gene, GABA pathway genes, and HSPG2 gene. Although a substantial number of genetic studies have investigated TD, many of the positive findings have not been replicated or are inconsistent, which could be due to differences in study design, sample size, and/or subject ethnicity. We expect that more refined research will be performed in the future to resolve these issues, which will then enable the genetic prediction of TD and clinical application thereof.

No Evidence for Association between Tyrosine Hydroxylase Gene Val81Met Polymorphism and Susceptibility to Tardive Dyskinesia in Schizophrenia

OBJECTIVE

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in dopamine biosynthesis. Because the TH Val81Met polymorphism is located in the amino-terminal regulatory domain of the tetrameric enzyme, it is a candidate marker for susceptibility to dopamine-related traits. We investigated the hypothesis that TH Val81Met polymorphism can influence susceptibility to tardive dyskinesia (TD) in schizophrenia.

METHODS

TH Val81Met polymorphism was analyzed by PCR-based methods in 83 schizophrenic patients with TD and 126 schizophrenic patients without TD, matched for antipsychotic drug exposure and other relevant variables.

RESULTS

There was no significant association of the genotype and allele frequencies determined by the TH Val81Met polymorphism between TD and non-TD patients. In addition, there was no significant difference in terms of total Abnormal Involuntary Movement Scale scores among the three genotype groups.

CONCLUSION

Within the limitations imposed by the size of the clinical sample, these findings suggest that the Val81Met polymorphism of the TH gene does not contribute significantly to the risk for TD.

Níveis de fibra em detergente neutro forrageiro na alimentação de ovelhas Santa Inês gestantes

Avaliaram-se o consumo, a digestibilidade aparente e o comportamento ingestivo de ovelhas no terço final de gestação com dietas contendo diferentes níveis de fibra em detergente neutro forrageiro (FDNf). Foram utilizadas 16 ovelhas adultas da raça Santa Inês, distribuídas em um delineamento inteiramente ao acaso, com quatro tratamentos: 9, 17, 26 e 35% de FDNf. Os consumos de matéria seca, matéria orgânica, proteína bruta, energia bruta, energia digestível e energia metabolizável não foram influenciados pelos tratamentos, e os consumos de fibra em detergente neutro (FDN) e de fibra em detergente ácido (FDA) aumentaram com maiores níveis de FDNf. As digestibilidades do FDN e FDA e o tempo gasto pelos animais com ruminação também aumentaram com maiores níveis de FDNf na dieta. Dietas com maior quantidade de FDNf influenciaram comportamento ingestivo e digestibilidade de ovelhas em fase final de lactação.

Genetic underpinnings of tardive dyskinesia: passing the baton to pharmacogenetics

Manifestation of tardive dyskinesia (TD) among schizophrenia subjects on long-term antipsychotic treatment with typical drugs has been a clinical concern. Despite its association with extrapyramidal symptoms, typical drugs are still routinely prescribed globally though marginally superior atypical drugs have long been available. The genetic component in the etiology of TD is well documented. Search for these determinants has led to a few consensus associations of CYP2D6 *10, CYP1A2*1F, DRD2 Taq1A (rs1800497), DRD3 Ser9Gly (rs6280) and MnSOD Ala9Val (rs4880) variants with TD. However, translation of these observations into the clinic has not been achieved so far. This review discusses the salient features of TD etiopathology, current status of TD genetics, interactions between genetic and nongenetic factors, some major drawbacks, challenges and expected focus in TD research over the next decade, with emphasis on pharmacogenetics.

No association between the brain-derived neurotrophic factor gene Val66Met polymorphism and tardive dyskinesia in schizophrenic patients

OBJECTIVE

This study investigated whether the brain-derived neurotrophic factor (BDNF) gene Val66Met single-nucleotide polymorphism (SNP) is associated with antipsychotic-induced tardive dyskinesia (TD) in schizophrenia.

METHODS

Genotyping was performed for the BDNF gene Val66Met SNP in Korean schizophrenic patients with (n=83) and without TD (n=126) who were matched for antipsychotic drug exposure and other relevant variables.

RESULTS

The frequencies of genotypes (chi2=2.37, p=0.306) and alleles (chi2=0.03, p=0.867) did not differ significantly between these two groups.

CONCLUSION

These findings suggest that the BDNF polymorphism does not play a major role in the susceptibility to TD in schizophrenic patients.

Neuroleptics and animal models: feasibility of oral treatment monitored by plasma levels and receptor occupancy assays

The administration of neuroleptics in animal models has been extensively reported and plays an important role in the study of schizophrenia. Our study was designed to address the following questions: (1) Is it possible to achieve steady-state receptor occupancy levels administering neuroleptics in drinking water? (2) Is there an appropriate dose to obtain clinically comparable receptor occupancies? (3) Is there a correlation between plasma drug levels and receptor occupancy? Thus, we tested three neuroleptic drugs administered in drinking water for 7 days. Plasma drug levels were measured, and in vivo receptor occupancy assays were performed in order to determine peak and trough dopamine D(2) receptor occupancies in striatal brain samples. Overall, our study indicates that in rodents the administration of appropriate doses of haloperidol and olanzapine in drinking water achieves receptor occupancies comparable to the clinical occupancy levels, but this appears not to be the case for clozapine.

No association between dopamine D4 receptor gene -521 C/T polymorphism and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotics. We evaluated whether a candidate functional polymorphism of the dopamine D4 receptor (DRD4) gene is associated with drug-induced TD in 209 Korean schizophrenic patients with TD (n = 83) and without TD (n = 126) who were matched for antipsychotic drug exposure and other relevant variables. There was no significant association of the genotype and allele frequencies determined by the -521 C/T SNP of DRD4 between TD and non-TD patients. In addition, there was no significant difference in terms of total Abnormal Involuntary Movement Scale scores among the 3 genotype groups. Within the limitations imposed by the size of the clinical sample, these findings suggest that the DRD4 -521 C/T SNP does not contribute significantly to the risk for TD.

Reversal of haloperidol-induced tardive vacuous chewing movements and supersensitive somatodendritic serotonergic response by buspirone in rats

Tardive dyskinesia (TD), a syndrome of involuntary hyperkinesias in the orofacial region that develops in patients chronically treated with neuroleptic agents is a major limitation of the therapy. Rats chronically treated with haloperidol exhibit vacuous chewing movements (VCMs) with the twitching of facial musculature and tongue protrusion. The syndrome is widely used as an animal model of TD. Evidence suggests a role of 5-hydroxytryptamine (5-HT; serotonin)-1A receptors in the pathogenesis and treatment of TD because repeated administration of haloperidol resulted in an increase in the effectiveness of 5-HT-1A receptors while drugs with agonist activity at 5-HT-1A receptors could attenuate haloperidol-induced VCMs. The present study was designed to test the hypothesis that a decrease in the responsiveness of somatodendritic 5-HT-1A receptors by the coadministration of buspirone could reverse the induction of VCMs and supersensitivity at 5-HT-1A receptors by haloperidol. Rats treated with haloperidol at a dose of 1 mg/kg twice a day for 2 weeks displayed VCMs with twitching of facial musculature that increased in a time dependent manner as the treatment continued to 5 weeks. Coadministration of buspirone attenuated haloperidol-induced VCMs after 2 weeks and completely prevented it after 5 weeks. The intensity of 8-hydroxy-2-di (n-propylamino) tetralin (8-OH-DPAT)-induced locomotion was greater in saline+haloperidol injected animals but not in buspirone+haloperidol injected animals. 8-OH-DPAT-induced decreases of 5-HT metabolism were greater in saline+haloperidol injected animals but not in buspirone+haloperidol injected animals. It is suggested that an impaired somatodendritic 5-HT-1A receptor dependent response is a major contributing factor in the pathophysiology of TD and a normalization of the somatodendritic response by drugs may help extending therapeutics in schizophrenia.

Reversal of haloperidol-induced extrapyramidal symptoms by buspirone: a time-related study

Effects of coadministration of buspirone were investigated on the time course of haloperidol-induced extrapyramidal symptoms in rats. Rats treated with haloperidol at a dose of 1 mg/kg exhibited impaired motor coordination and a decrease in exploratory activity. Coadministration of buspirone at a dose of 1 mg/kg attenuated haloperidol-induced deficits of motor coordination but no effect was produced on the deficits of exploratory activity, possibly because of a 'floor effect'. Long-term administration of haloperidol (1 mg/kg) twice a day for 5 weeks did not produce tolerance to haloperidol-induced deficits of exploratory activity. The deficits of motor coordination were attenuated after 4-5 weeks of drug administration. Coadministration of buspirone for 3-5 weeks attenuated and reversed haloperidol-induced deficits of exploratory activity. Deficits of motor coordination were smaller in rats cotreated with buspirone after 1 week but not after 2-5 weeks. Administration of haloperidol for 2 weeks elicited vacuous chewing movements with twitching of facial musculature that increased in a time-dependent manner as the treatment continued to 5 weeks. Animals cotreated with buspirone exhibited a gradual reversal of the response during 2-5 weeks of treatment. The mechanism involved in the attenuation/reversal of haloperidol-induced extrapyramidal symptoms by buspirone is discussed. Prior administration of buspirone for 2 weeks may be of help in the improvement of extrapyramidal symptoms induced by antipsychotic drugs.

Multidose risperidone treatment evaluated in a rodent model of tardive dyskinesia

Risperidone is a second-generation antipsychotic that lacks acute motor side effects at low doses (<6 mg/day), but above this level is associated with parkinsonism and akathesia. The literature suggests an association between acute motor side effects and tardive dyskinesia (TD); therefore, we hypothesized that low dose levels of risperidone will spare TD. As clinical studies of TD liability with fixed doses of risperidone are difficult to conduct, we tested low and high doses of risperidone in a rodent model of TD, vacuous chewing movements (VCMs) production. Low doses of risperidone (1.5 mg/kg/day) resulted in control levels of VCMs after 6 months of treatment, whereas high doses of risperidone (6 mg/kg/day) produced VCM in the same range as haloperidol. Plasma drug levels are reported. If this animal model predicts TD risk in humans, the TD liability with low-dose risperidone is at a placebo level, whereas higher doses show haloperidol-like TD risk, as predicted from the acute motor effects.

The effect of chronic administration of sarizotan, 5-HT1A agonist/D3/D4 ligand, on haloperidol-induced repetitive jaw movements in rat model of tardive dyskinesia

Dyskinesia is the most troublesome side effect in long-term treatment of both Parkinson's disease (PD) and schizophrenia. The 5-HT1A agonist and D3/D4 ligand sarizotan [Bartoszyk, G.D., van Amsterdam, C., Greiner, H.E., Rautenberg, W., Russ, H., Seyfried, C.A., 2004. Sarizotan, a serotonin 5-HT1A receptor agonist and dopamine receptor ligand. 1. Neurochemical profile. J. Neural Transm. 111, 113-126.] is in clinical development for the treatment of PD-associated dyskinesia. Because 5-HT1A agonists are known to counteract antipsychotic-induced motor side effects, sarizotan was investigated for its effects in two rat models of tardive dyskinesia (TD). The acute administration of sarizotan (0.17-13.5 mg/kg i.p.) reduced episodes of SKF 38393-induced repetitive jaw movements (RJM) in rats with a maximal effect at 1.5 mg/kg. In a chronic study, sarizotan (0.04-9 mg/kg/day), administered in the drinking water for 7 weeks during withdrawal from chronic haloperidol treatment (1.5 mg/kg/day), dose-dependently reversed haloperidol-induced RJM, significant at the doses of 1.5 and 9 mg/kg. Agonism at 5-HT1A receptors may be mediating the inhibitory effect of sarizotan on RJM in rat models of tardive dyskinesia.

Association of dopaminergic and serotonergic genes with tardive dyskinesia in patients with chronic schizophrenia

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotic drugs that are dopamine D2 receptor blockers. Serotonin receptor antagonism has been proposed as a common mechanism contributing to the low extrapyramidal side effect profile of atypical antipsychotic drugs. We evaluated candidate dopamine and serotonin genes for association with drug-induced TD. We examined three polymorphisms in the dopamine D2 receptor gene (DRD2), two sites in the 3' region of the dopamine transporter (DAT) gene, two sites in the promoter and coding region of the dopamine D4 (DRD4) receptor gene, as well as polymorphic sites in the serotonin 6 receptor gene, the serotonin transporter gene and the tryptophan hydroxylase gene, for association with TD susceptibility. Schizophrenic patients with (n=59) and without TD (n=63), matched for antipsychotic drug exposure and other relevant variables, were studied. No significant associations were found. Within the limitations imposed by the size of the clinical sample, these findings suggest that the above polymorphic loci do not contribute significantly to risk for TD. Further examination of loci that yielded positive results at a trend level and investigation of other candidate genetic loci coding for antipsychotic drug targets is warranted.

Relationship of orofacial movements to behavioural repertoire as assessed topographically over the course of 6-month haloperidol treatment followed by 4-month withdrawal

RATIONALE

Late-onset vacuous chewing movements (VCMs) arise in a significant proportion of rats treated chronically with conventional antipsychotic drugs. Given their common action to block dopamine D2-like receptors, VCMs may be related to changes in dopaminergic function; if so, other typical dopamine-mediated behaviours might be altered also.

OBJECTIVE

To examine this hypothesis, behavioural repertoire was studied topographically over the course of chronic treatment and withdrawal.

METHODS

Animals were injected with haloperidol decanoate 28 mg/kg IM, or vehicle, every 3 weeks for 27 weeks, and then maintained without treatment for a further 18 weeks. Immediately before each injection and during withdrawal, VCMs and other topographies of behaviour were assessed.

RESULTS

In both control and haloperidol-treated rats, exploratory behaviours declined over the study, indicating habituation effects. Conversely, VCMs emerged after 6 weeks of treatment with haloperidol and persisted after withdrawal; VCM and locomotion were not related, indicating that in treated rats, increased VCMs are not an artifact of reduced locomotion. Treated animals with VCMs evidenced increases in buccal tremor and grooming behaviour relative to those without VCMs, although no clear relationship to the emergence of VCMs was established; there were no material differences in any other topographies of behaviour.

CONCLUSION

The effect of long-term treatment with haloperidol to induce VCMs is not reflected in fundamental changes in dopamine-mediated behavioural topography but, rather, appears to affect neural mechanisms involved in orofacial movement preferentially.

Central administration of the neurotensin receptor antagonist SR48692 attenuates vacuous chewing movements in a rodent model of tardive dyskinesia

Tardive dyskinesia is a movement disorder that develops in 20-30% of patients treated with chronic neuroleptics. Whilst the pathogenesis of tardive dyskinesia remains unclear, altered expression of neuropeptides in the basal ganglia has been implicated in its emergence. The peptide neurotensin is expressed in both dopamine D1 receptor-bearing neurons of the direct striatonigral pathway and dopamine D2 receptor-bearing neurons of the indirect striatopallidal pathway. Increased levels of striatal neurotensin messenger RNA (mRNA) are reported following chronic neuroleptic therapy. Chronic treatment with the typical antipsychotic haloperidol elicits neurotensin immunoreactivity in a large number of striatopallidal and a modest number of striatonigral projection neurons, whilst treatment with the potent dopamine releaser, methamphetamine, induces intense neurotensin immunoreactivity in striatonigral projection neurons. In order to determine whether increased levels of striatal neurotensin mRNA in the direct striatonigral or the indirect striatopallidal pathway play a more influential role in the development of tardive dyskinesia, we explored the effects of a specific neurotensin antagonist in a rodent model (vacuous chewing movements [VCMs] induced by chronic neuroleptics). Three groups of animals received injections of fluphenazine decanoate (25 mg/kg) or its vehicle sesame oil every 3 weeks for at least 18 weeks. They were then surgically implanted with bilateral guide cannulae aimed at the striatum, the substantia nigra pars reticulata, or the globus pallidus respectively. After recovery, animals were infused with 2-[(1-(7-chloro-4-quinolinyl)-5-(2,6-imethoxyphenyl)pyrazol-3-yl)carbonylamino]tricyclo(3.3.1.1.(3.7))decan-2-carboxylic acid (SR48692; 0.25, 0.50, and 1.0 nmol/microl), or its vehicle (10% dimethyl sulfoxide [DMSO] in saline) and observed for 60 min. Intra-striatal, intra-nigral or intra-pallidal infusion of SR48692 attenuated neuroleptic-induced VCMs. These findings lend further support to a role for neurotensin in the development of VCMs but do not clarify which pathway plays a more important role. Thus, treatments that reduce or prevent the effects of increased neurotensin expression and release may be useful in the management of tardive dyskinesia.

Brain sites of movement disorder: genetic and environmental agents in neurodevelopmental perturbations

In assessing and assimilating the neurodevelopmental basis of the so-called movement disorders it is probably useful to establish certain concepts that will modulate both the variation and selection of affliction, mechanisms-processes and diversity of disease states. Both genetic, developmental and degenerative aberrations are to be encompassed within such an approach, as well as all deviations from the necessary components of behaviour that are generally understood to incorporate "normal" functioning. In the present treatise, both conditions of hyperactivity/hypoactivity, akinesia and bradykinesia together with a constellation of other symptoms and syndromes are considered in conjunction with the neuropharmacological and brain morphological alterations that may or may not accompany them, e.g. following neonatal denervation. As a case in point, the neuroanatomical and neurochemical points of interaction in Attention Deficit and Hyperactivity disorder (ADHD) are examined with reference to both the perinatal metallic and organic environment and genetic backgrounds. The role of apoptosis, as opposed to necrosis, in cell death during brain development necessitates careful considerations of the current explosion of evidence for brain nerve growth factors, neurotrophins and cytokines, and the processes regulating their appearance, release and fate. Some of these processes may possess putative inherited characteristics, like alpha-synuclein, others may to greater or lesser extents be endogenous or semi-endogenous (in food), like the tetrahydroisoquinolines, others exogenous until inhaled or injested through environmental accident, like heavy metals, e.g. mercury. Another central concept of neurodevelopment is cellular plasticity, thereby underlining the essential involvement of glutamate systems and N-methyl-D-aspartate receptor configurations. Finally, an essential assimilation of brain development in disease must delineate the relative merits of inherited as opposed to environmental risks not only for the commonly-regarded movement disorders, like Parkinson's disease, Huntington's disease and epilepsy, but also for afflictions bearing strong elements of psychosocial tragedy, like ADHD, autism and Savantism.

Dopamine receptor supersensitivity: an outcome and index of neurotoxicity

The characteristic feature of neurotoxicity is a definable lesion which can account for observed deficits, corresponding to loss of nuclei or axonal fibers normally comprising a specific pathway or tract. However, with ontogenetic lesions, the operative definition fails. In rats lesioned as neonates with 6-hydroxydopamine (6-OHDA), near-total destruction of dopamine- (DA-) containing nerves is produced, and this itself is definable. However, the most prominent feature of rats so-lesioned is the DA receptor supersensitivity (DARSS) that develops and then persists throughout the lifespan. DA D(1) receptors show overt supersensitivity to agonists producing vacuous chewing movements (VCMs), while D(1) receptors associated with locomotor activity have a latent supersensitivity that must be unmasked by repeated D(1) or D(2) agonist treatments - a 'priming' phenomenon. This D(1) DARSS is not usually associated in either a change in D(1) receptor number (B(max)) or affinity (K(d)). In contrast to D(1) DARSS, D(2) receptors are not so predictably supersensitized by a lesion of DA neurons. In reality, the permanently exaggerated response to an agonist by supersensitized receptors is per se a manifestation of neurotoxicity. Despite dramatic behavioral responses mediated by supersensitized receptors, DARSS has not been easy to correlate with enhanced production of second messengers or early response genes. Altered signaling (i.e., neuronal cross-talk) in defined pathways may represent the mechanism that produces so-called receptor supersensitization. Long-lived agonist-induced behavioral abnormality, with or without anatomic evidence of a neuronal lesion, is one of the products of DA D(1) receptor supersensitization -- itself an index of neurotoxicity.

Blockade of nigral and pallidal opioid receptors suppresses vacuous chewing movements in a rodent model of tardive dyskinesia

Chronic neuroleptic treatment leads to the development of tardive dyskinesia in 20-30% of patients. While the pathogenesis of tardive dyskinesia remains elusive, altered opioid peptide function in striatal projection pathways of the basal ganglia has been implicated. Using a rodent model of vacuous chewing movements induced by chronic neuroleptic administration, we investigated regional involvement of opioid transmission in tardive dyskinesia. We examined the role of dynorphin in the direct striatonigral pathway by infusing nor-binaltorphimine, a selective kappa opioid receptor antagonist, into the substantia nigra pars reticulata. As well, infusions of naloxone (a non-specific opioid receptor antagonist), D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide (CTOP; a mu opioid receptor antagonist) or naltrindole (a delta opioid receptor antagonist) into the globus pallidus were used to establish the contribution of the striatopallidal pathway. Chronic fluphenazine treatment (25 mg/kg i.m. every 3 weeks for 18 weeks) resulted in a robust increase in vacuous chewing movements. Infusion of nor-binaltorphimine (5.0 nmol) into the substantia nigra pars reticulata significantly attenuated vacuous chewing movements. Infusion of naloxone (0.5 and 2.0 nmol) into the globus pallidus also significantly attenuated vacuous chewing. Infusion of naltrindole into the globus pallidus blocked vacuous chewing at all doses administered (0.5, 1.0, 2.0 nmol) while CTOP was only effective at the two higher doses. From these results we suggest that increases in dynorphin in the direct striatonigral pathway and enkephalin in the indirect striatopallidal pathway following chronic neuroleptic administration are both likely to contribute to tardive dyskinesia.

Dopaminergic synapses in the matrix of the ventrolateral striatum after chronic haloperidol treatment

Antipsychotic drugs (APD) are used in the treatment of schizophrenia and other psychotic disorders and exert their effects, in part, through dopamine receptor blockade. APD treatment causes many changes in the brains of humans and experimental animals including therapeutic, pathologic, or changes associated with motor side effects. Typical APD given chronically to animals induce behavioral sequelae that mimic tardive dyskinesia in several ways. Our previous work has shown that chronic treatment with haloperidol decreases striatal synaptic density but that symmetric synapses are lost only in rats that develop oral dyskinesias. The goals of this study were to determine if the density of dopaminergic terminals was affected by chronic haloperidol treatment and/or correlated with dyskinesias. Rats were given haloperidol (1.5 mg/kg/rat) or water, as a control. After 6 months of treatment, rats were divided into nondyskinetic or dyskinetic groups according to the behavior scores determined in the last month. Striatal volume was similar between controls and drug-treated rats. Synaptic density, calculated using stereological methods, was obtained from the matrix of the ventrolateral striatum. The density of symmetric synapses (mean +/- SD, per 100/microm(3)) formed by tyrosine hydroxylase (TH) containing terminals in haloperidol treated rats (3.58 +/- 1.64) was not significantly different from that of controls (3.06 +/- 1.00). The density of TH-labeled terminals forming symmetric synapses in the nondyskinetic group (3.65 +/- 1.67) vs. the dyskinetic group (3.54 +/- 1.73) was similar and neither was different from that of the controls. These data indicate that terminals other than dopaminergic ones form fewer symmetric synapses in dyskinetic rats. Moreover, these data have implications for interpreting results obtained in humans treated with typical antipsychotic drugs.

The vacuous chewing movement (VCM) model of tardive dyskinesia revisited: is there a relationship to dopamine D(2) receptor occupancy?

Tardive dyskinesia (TD) is a late side effect of long-term antipsychotic use in humans, and the vacuous chewing movement (VCM) model has been used routinely to study this movement disorder in rats. Recent receptor occupancy studies in humans and rats have found that antipsychotics given in doses which lead to moderate levels of D(2) receptor blockade can achieve optimal clinical response while minimizing the emergence of acute motor side effects. This suggests that clinicians may have been using inappropriately high doses of antipsychotics. A review of the existing VCM literature indicates that most animal studies have similarly employed antipsychotic doses that are high, i.e. doses that lead to near complete D(2) receptor saturation. To verify whether the incidence or severity of VCMs would decrease with lower antipsychotic doses, we conducted initial experiments with different doses of haloperidol (HAL) given either as repeated daily injections or as depot injections over the course of several weeks. Our results demonstrate that (1) the incidence of VCMs is significantly related to HAL dose, and (2) significant levels of VCMs only emerge when haloperidol is continually present. These findings are consistent with the possibility that total D(2) occupancy, as well as 'transience' of receptor occupation, may be important in the development of late-onset antipsychotic-induced dyskinetic syndromes.

Sub-chronic treatment with classical but not atypical antipsychotics produces morphological changes in rat nigro-striatal dopaminergic neurons directly related to "early onset" vacuous chewing

In the present work, we investigated if an impairment of dopaminergic neurons after subchronic haloperidol treatment might be a possible physiopathologic substrate of the "early onset" vacuous chewing movements (VCMs) in rats. For this purpose, different antipsychotics were used to analyse a possible relationship between VCMs development and morphological alterations of tyrosine-hydroxylase-immunostained (TH-IM) neurons. Rats treated twice a day with haloperidol displayed a significant increase of VCMs that was both time- (2-4 weeks) and dose (0.1-1 mg/kg) dependent. Immunocytochemical analysis showed a shrinkage of TH-IM cell bodies in substantia nigra pars compacta and reticulata and a reduction of TH-immunostaining in the striatum of haloperidol treated rats with the arising of VCMs. No differences were observed in TH-IM neurons of ventral tegmental area and nucleus accumbens vs. control rats. The atypical antipsychotics risperidone (2 mg/kg, twice a day), amisulpride (20 mg/kg, twice a day) and clozapine (10 mg/kg, twice a day) did not produce any nigro-striatal morphological changes or VCMs. TH-IM nigro-striatal neuron morphological alterations and VCMs were still present after three days of withdrawal in rats treated for four weeks with haloperidol (1 mg/kg). Both the main morphological changes and the behavioural correlate disappeared after three weeks of withdrawal. These results suggest that haloperidol induces a morphological impairment of the dopaminergic nigro-striatal neurons which is directly associated with the arising, permanency and disappearance of VCMs in rats.

Tardive dyskinesia model in the common marmoset

Thirteen adult common marmosets (Callithrix jacchus) were given once-monthly injections of haloperidol decanoate (5-15 mg/kg i.m.) for one year. Thereafter, drug-free and treatment periods alternated at 3-month intervals. After 2.5 to 14 months, 12 monkeys showed symptoms of tardive dyskinesia (TD), such as periocular and perioral twitchings, tongue protrusions, masticatory movements, and choreic movements in arms and legs. When TD symptoms were evident, the periodic treatment was interrupted and symptoms persisted for at least 5 months after the last haloperidol dose, worsened by injection of the anticholinergic drug biperiden. An injection of nondepot haloperidol (0.12 or 0.25 mg/kg) produced a reduction of TD symptoms. At the end of the study, nondepot haloperidol was injected once a week at two doses (0.12 and 0.25 mg/kg i.m.). A syndrome of excitation with peculiar behavior, interpreted as acute dystonia, was precipitated in all animals. The animals showed sustained retrocollis, climbing upside down, biting the perch, repetitive turnings, and frequent backward movements. The dystonic movements lasted approximately 6 hours and were reduced but not completely extinguished by biperiden (0.1 mg/kg). The TD syndrome registered in marmosets may provide a useful model for screening new antipsychotics for their propensity to induce TD.

Lack of association between a functional polymorphism of the cytochrome P450 1A2 (CYP1A2) gene and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a common side effect of long-term medication with typical neuroleptics. TD presents itself by abnormal involuntary movements and may lead to a potentially disabling and chronic clinical course. A vast majority of patients suffering from schizophrenia are smokers. Smoking has been reported to induce the activity of the CYP1A2 enzyme, which is an established metabolic pathway within the disposition of antipsychotics. Recently, a C-->A genetic polymorphism in the first intron of the CYP1A2 gene was reported to influence CYP1A2 activity in smokers. Subsequently, a pharmacogenetic study in 85 U.S. patients with schizophrenia (44 smokers, 41 individuals with unknown smoking status) showed the C/C genotype to be associated with higher TD severity (measured by the Abnormal Involuntary Movement Scale, AIMS) than the A/C or A/A genotype. This finding prompted us to investigate whether this effect was also present in a larger German sample of 119 patients with schizophrenia (82 smokers, 37 individuals with unknown smoking status). However, we could not replicate the reported association. The median AIMS scores did not differ between individuals with the A/A, A/C, or C/C genotypes. In an additional analysis, we compared the genotypic and allelic distribution among individuals grouped according to the criteria established by Schooler and Kane [1982: Arch Gen Psychiatry 39:486-487] (persistent TD vs. absent TD). We did not observe a differential genotypic or allelic distribution between the two diagnostic groups. Thus, our results do not support the hypothesis that the C-->A polymorphism in the CYP1A2 gene is involved in the etiology of TD in the German population.

Persistent alterations in dendrites, spines, and dynorphinergic synapses in the nucleus accumbens shell of rats with neuroleptic-induced dyskinesias

Chronic treatment of humans or experimental animals with classical neuroleptic drugs can lead to abnormal, tardive movements that persist long after the drugs are withdrawn. A role in these neuroleptic-induced dyskinesias may be played by a structural change in the shell of the nucleus accumbens where the opioid peptide dynorphin is upregulated in treated rats that show vacuous chewing movements (VCMs). The shell of the nucleus accumbens normally contains a dense plexus of dynorphinergic fibers especially in its caudomedial part. After 27 weeks of haloperidol administration and 18 weeks of withdrawal, the immunoreactive labeling of this plexus is intensified when compared with that after vehicle treatment. In addition, medium spiny neurons here show a significant increase in spine density, dendritic branching, and numbers of terminal segments. In the VCM-positive animals, the dendritic surface area is reduced, and dynorphin-positive terminals contact more spines and form more asymmetrical specializations than do those in animals without the syndrome (VCM-negative and vehicle-treated groups). Persistent, neuroleptic-induced oral dyskinesias could therefore be caused by incontrovertible alterations, involving terminal remodeling or sprouting, to the synaptic connectivity of the accumbal shell.

Enhancement of laminar FosB expression in frontal cortex of rats receiving long chronic clozapine administration

The frontal cortex (FrC) and cingulate cortex (CgC) are critical sites for normal cognitive function, as well as cognitive dysfunction in schizophrenia. Thus, modulation of synaptic transmission within these cortical areas may, in part, account for the therapeutic actions of antipsychotic drugs such as haloperidol and clozapine. FosB and DeltaFosB are immediate-early gene (IEG) products sensitive to changes in response to chronic neuroleptic drug administration. We quantitatively examine whether there are light microscopic regional and/or laminar variations in FosB or DeltaFosB in the FrC or CgC of normal adult rats, or animals receiving 6 months administration of either drinking water clozapine, or depot haloperidol. Only animals receiving chronic haloperidol developed vacuous chewing movements, the equivalent of tardive dyskinesia in humans. In control animals, the deep and superficial layers of the FrC showed a higher area density of FosB, but not DeltaFosB immunoreactive cells than the medial layers of FrC or any of the CgC layers. In animals receiving clozapine, but not haloperidol there was increase in the area density of FosB immunoreactive neurons in all FrC layers, but the major increase occurs in medial layers. These findings suggest that FosB expression identifies those FrC neurons that are most active during normal waking behaviors and are further activated following chronic administration of atypical neuroleptics without motor side effects. The results also indicate that the actions of clozapine are attributed in large part to modulation of the output of frontal cortical pyramidal neurons residing in the medial layers.

Traditional and new antipsychotic drugs differentially alter neurotransmission markers in basal ganglia-thalamocortical neural pathways

The effects of three chronically administered antipsychotic drugs on selected neurochemical markers of dopaminergic and GABAergic transmission were compared within the cerebral regions making up the basal ganglia-thalamocortical parallel processing neuronal pathways. All three drugs reduce psychosis in humans, whereas only haloperidol, but not olanzapine or sertindole, induce purposeless oral chewing movements (CMs) in rats or cause high rates of parkinsonism or tardive dyskinesia in humans. Male Sprague Dawley rats were treated with haloperidol, sertindole, or olanzapine delivered in drinking water for 6 months at doses which produce drug plasma levels in rat in the human therapeutic range. Results show the expected dopamine D2 receptor upregulation in striatum predominantly with haloperidol, although mild D2 upregulation was apparent in striatum after olanzapine. GAD67 mRNA was increased in striatum and decreased in globus pallidus by haloperidol and sertindole, but not by olanzapine. In the substantia nigra pars reticulata (SNR), both olanzapine and sertindole failed to induce GABA(A) receptor upregulation or D1 receptor downregulation, but haloperidol did both, confirming a previous report. In thalamus, all three drugs increased GAD expression in the reticular nucleus, whereas only haloperidol decreased GABA(A) binding in the mediodorsal nucleus, actions consistent with a reduction in nigrothalamic, GABA-mediated neural transmission. These results are consistent with the idea that the two new antipsychotics tested have mild and regionally restricted actions within the basal ganglia nuclei and a common action on increasing GAD expression in the reticular nucleus of the thalamus (RtN). Haloperidol, in contrast, has a broad and potent action in basal ganglia, causing changes in SNR and in the mediodorsal nucleus, while also altering GAD mRNA in RtN, potentially reflective of its dyskinetic and antipsychotic actions.

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.

Effect of chronic olanzapine treatment on striatal synaptic organization

Our previous work has shown that chronic haloperidol treatment decreases striatal symmetric synapses preferentially in rats which develop oral dyskinesias (vacuous chewing movements (VCMs)). The present experiment tests the hypothesis that olanzapine, which does not cause dyskinesia in humans or rats, would not cause the ultrastructural changes produced by haloperidol. After 6 months of treatment, VCM scores for the olanzapine group (5.1 +/- 4.5) were similar to those of controls (5.2 +/- 3.9), whereas rats in the haloperidol group were either nondyskinetic (4.3 +/- 2.2) or dyskinetic (16.9 +/- 6.7). The volume of the striatum (mm(3)), did not differ among the groups: control, 37.5 +/- 4.7; olanzapine, 36.4 +/- 4.3; haloperidol, nondyskinetic, 40.5 +/- 6.3; haloperidol, dyskinetic, 36.6 +/- 5.9. Synaptic density (per 1 microm(3)), obtained from the central region of the striatum, did not differ between the olanzapine (0.699 +/- 0.146) and control groups (0.652 +/- 0.108). The number of asymmetric synapses in the olanzapine group (0.624 +/- 0.136) was also similar to that of controls (0.550 +/- 0.090). The number of symmetric synapses in the olanzapine group (0.074 +/- 0.032) was not significantly different from that of controls (0.096 +/- 0.043). Thus, olanzapine, in contrast to haloperidol, did not produce dyskinesias or synapse loss. These results strengthen the correlation between the expression of VCMs and striatal synaptic changes and indicate that olanzapine has fewer behavioral and anatomical side effects than does haloperidol.

Neurotoxicity associated with neuroleptic-induced oral dyskinesias in rats. Implications for tardive dyskinesia?

Tardive dyskinesia is a serious motor side effect of long-term treatment with neuroleptics, with an unknown pathophysiologic basis. Brain damage and aging are prominent risk-factors, and together with the persistent character of the disorder, it is likely that long-lasting neuronal changes are involved in the pathogenesis. It has been hypothesized that striatal neurodegeneration caused by excitotoxic mechanisms and oxidative stress may play an important role in the development of the disorder, and the scope of the present work is to review the evidence supporting this hypothesis. The rat model of tardive dyskinesia has been used extensively in the field, and the usefulness of this model will be discussed. Neuroleptics are able to induce oxidative stress in vitro and increase striatal glutamatergic activity in rats, which may lead to toxic effects in the striatum. Drugs that block excitotoxicity inhibit the development of persistent oral dyskinesia in the rat model, and impaired energy metabolism leads to increased frequency of oral dyskinesia. There are also signs of altered striatal histology in rats with high frequency of oral dyskinesia. Furthermore, markers of increased oxidative stress and glutamatergic neurotransmission have been found in the cerebrospinal fluid of patients with tardive dyskinesia. In conclusion, several lines of evidence implicate neurotoxic events in the development of neuroleptic induced tardive dyskinesia.

The preventative role of antioxidants (selegiline and vitamin E) in a rat model of tardive dyskinesia

BACKGROUND

We examined the potential protective effects of two potent antioxidants, selegiline and vitamin E, in a rodent model of tardive dyskinesia (TD), viz. neuroleptic-induced spontaneous orofacial movements.

METHODS

Rats were treated with fortnightly injections of fluphenazine decanoate for 12 weeks, and examined at baseline and at fortnightly intervals for vacuous chewing movements, mouth tremors and tongue protrusions.

RESULTS

The administration of fluphenazine led to a progressive increase of all three types of orofacial movements. In the first study, the impact of the concomitant administration of selegiline on orofacial movements was examined. Selegiline led to a reduction in orofacial movements in neuroleptic-treated rats to the level of control rats not being administered a neuroleptic drug. In the second study, rats were fed diets either high or low in their vitamin E content. High and low vitamin E diets did not significantly affect neuroleptic-induced orofacial movements.

CONCLUSIONS

Our studies provide some support for the hypothesis that oxidative injury may play a role in the genesis of neuroleptic-induced movement disorder, and prompt further examination of this hypothesis in both animals and humans.

The neuropathological effects of antipsychotic drugs

In addition to their neurochemical effects, antipsychotic (neuroleptic) drugs produce structural brain changes. This property is relevant not only for understanding the drugs' mode of action, but because it complicates morphological studies of schizophrenia. Here the histological neuropathological effects of antipsychotics are reviewed, together with brief mention of those produced by other treatments sometimes used in schizophrenia (electroconvulsive shock, lithium and antidepressants). Most data come from drug-treated rats, though there are also some human post-mortem studies with broadly congruent findings. The main alteration associated with antipsychotic medication concerns the ultrastructure and proportion of synaptic subpopulations in the caudate nucleus. In rats, synapses and dendrites in lamina VI of the prefrontal cortex are also affected. The changes are indicative of a drug-induced synaptic plasticity, although the underlying mechanisms are poorly understood. Similarly, it is unclear whether the neuropathological features relate primarily to the therapeutic action of antipsychotics or, more likely, to their predisposition to cause tardive dyskinesia and other motor side-effects. Clozapine seems to cause lesser and somewhat different alterations than do typical antipsychotics, albeit based on few data. There is no good evidence that antipsychotics cause neuronal loss or gliosis, nor that they promote neurofibrillary tangle formation or other features of Alzheimer's disease.

The effect of novel antipsychotics in rat oral dyskinesia

1. The effect of the D1 agonist SKF38393 and the 5HT2C agonist m-CPP on repetitive jaw movements (RJM) was studied in rats. Acute administration of SKF38393 and/or m-CPP induced RJM in a dose dependent manner. In rats treated with both drugs, RJM responses were about equal to the sum of those obtained with each drug alone. 2. The induction of RJM by SKF38393 was somewhat lower in rats pretreated with 5HT2C receptor antagonist, mianserin, whereas mianserin severely reduced RJM induced by m-CPP alone. 3. D1 antagonist SCH23390 inhibited SKF38393 induced RJM but had no effect on m-CPP induced chewing behavior. 4. The present study confirms earlier evidence that D1 agonists used at optimal doses for the induction of RJM do not involve the serotonergic system in a significant way. It does, however, implicate the system in the emergence of drug induced oral behavior in rats. 5. The effect of the atypical antipsychotics, clozapine, olanzapine and risperidone was studied on SKF38393 and m-CPP induced RJM. Pretreatment with the atypical antipsychotics clozapine and olanzapine inhibit SKF38393 and m-CPP induced RJM. Pretreatment with risperidone inhibits m-CPP induced oral behavior in rats while increases dose dependently SKF38393 induced RJM.

Enhancement of N-methyl-D-aspartate (NMDA) immunoreactivity in residual dendritic spines in the caudate-putamen nucleus after chronic haloperidol administration

Glutamate receptors of the N-methyl-D-aspartate (NMDA) subtype in the caudate-putamen nucleus (CPN) have been implicated in the adverse motor effects produced by chronic administration of the typical antipsychotic drug haloperidol. To determine the functionally relevant sites, we examined the electron microscopic immunocytochemical localization of the R1 receptor subunit (NMDAR1) in the dorsolateral CPN of rats receiving 4 months of biweekly depot intramuscular injections of either haloperidol or vehicle. In all animals, NMDAR1 immunoreactivity was seen mainly in dendritic spines, but was also present in a few somata and dendrites of spiny neurons, axon terminals, and glia. In comparison with controls, the dissector stereological analysis showed a significant reduction in the numerical density of total NMDAR1-labeled and unlabeled dendritic spines in the dorsolateral CPN after haloperidol administration. When labeled spines were identified separately based exclusively on the presence of immunoreactivity within a single plane of section, there was, however, a significant increase in the numerical density of NMDAR1-containing spines in haloperidol vs. control animals. This increase was not seen using a classic dissector, suggesting that the enhancement was mainly attributed to more frequent detection of spines having higher levels of NMDA immunoreactivity. Our results are the first to identify dendritic spines in the dorsolateral CPN as preferential sites for the regulated expression of NMDA receptors following chronic administration of haloperidol.

The regulation of forebrain dopamine transmission: relevance to the pathophysiology and psychopathology of schizophrenia

Since the discovery that the therapeutic efficacy of antipsychotic drugs was significantly correlated to their ability to block dopamine D2 receptors, abnormal dopamine transmission in the forebrain has been postulated to underlie psychosis in schizophrenia. In the past 15 years, an impressive amount of clinical and basic research aimed at the study of schizophrenia has indicated that prefrontal and temporal cortical abnormalities may be more important in the etiology of many of the symptoms of schizophrenia, including psychosis. However, the cortical systems that appear to have structural and/or metabolic abnormalities in schizophrenia patients potently regulate forebrain dopamine transmission through a number of mechanisms. In turn, dopamine modulates excitatory transmission mediated by frontal and temporal cortical projections to the basal ganglia and other regions. The present review summarizes the multiple interactions between forebrain DA systems and frontal and temporal corticostriatal transmission. It then examines the role of these interactions in normal behaviors and the psychopathology of schizophrenia.

The relationship between oral dyskinesias produced by long-term haloperidol treatment, the density of striatal preproenkephalin messenger RNA and enkephalin peptide, and the number of striatal neurons expressing preproenkephalin messenger RNA in rats

Neuroleptic-induced oral dyskinesias in rats, a putative analogue to human tardive dyskinesia, may be due to excitotoxic degeneration within the striatum. Haloperidol treatment for 34 weeks increased the optical density of preproenkephalin messenger RNA in individual striatal neurons and enkephalin peptide in the neuropil, regardless of the level of oral dyskinesia produced. However, using unbiased stereological methods, an increased number of striatal neurons expressing preproenkephalin messenger RNA was observed only in rats that did not develop pronounced oral dyskinesias during haloperidol treatment. Said in another manner, the haloperidol-treated animals that developed pronounced oral dyskinesias, failed to produce an increase in the number of neurons expressing preproenkephalin messenger RNA. These results indicate that the mechanism by which neuroleptics induce oral dyskinesias in rats, and perhaps tardive dyskinesia in humans, involves a functional disturbance or even damage to a subpopulation of enkephalinergic neurons in the striatum.

A phosphoinositide-linked dopamine D1 receptor mediates repetitive jaw movements in rats

BACKGROUND

We have demonstrated that rats injected with D1 agonists SKF 38393 or A68930 demonstrate repetitive jaw movements (RJM). These agonist-induced movements in rats are similar in their appearance to those induced in rats by long-term treatment with antipsychotic drugs. Over recent years D-1 receptors were discovered which showed linkage not only to c-AMP but also to PI hydrolysis. We examined the effect of EEDQ inactivation of D1 receptors on D-1 mediated PI hydrolysis and RJM.

METHODS

Twenty four hours following EEDQ or vehicle administration D-1 agonists or vehicle were administered. The number of RJM episodes was assessed in EEDQ and vehicle treated rats. D-1 receptor density and inositol phosphate formation were determined in the striata.

RESULTS

EEDQ administration resulted, 24 hours later, in 70-80% selective depletion of D-1 receptors in the striata but did not modify the rate of RJM induced by D-1 agonists. There was no significant difference in D-1 mediated PI hydrolysis in EEDQ treated rats when compared to vehicle treated group.

CONCLUSIONS

The present data support the earlier demonstration of D-1 agonist induced RJM, an effect mediated by a subpopulation of a D-1 receptor subtype and constitute the first behavioral evidence for the existence of a behavioral response mediated by D-1 like dopamine receptors linked to an alternate second messenger system-PI hydrolysis.

Oral Dyskinesias and striatal lesions in rats after long-term co-treatment with haloperidol and 3-nitropropionic acid

The pathophysiologic basis of tardive dyskinesia remains unclear. It has been proposed that tardive dyskinesia may be a result of excitotoxic neurodegeneration in the striatum caused by a neuroleptic-induced increase in striatal glutamate release and impaired energy metabolism. To investigate this hypothesis, haloperidol decanoate (38 mg/kg/four weeks intramuscularly) and the succinate dehydrogenase inhibitor 3-nitropropionic acid (8 mg/kg/day via subcutaneous osmotic mini-pumps), were administered alone or together for 16 weeks to four-months-old rats. Control rats received sesame oil intramuscularly and had empty plastic tubes subcutaneously. Vacuous chewing movements, a putative analogue to human tardive dyskinesia, were recorded during and after drug treatment. Haloperidol alone, 3-nitropropionic acid alone, and 3-nitropropionic acid+haloperidol treatments induced an increase in vacuous chewing movements. However, vacuous chewing movements were more pronounced and appeared earlier in rats treated with 3-nitropropionic acid+haloperidol. After drug withdrawal, increases in vacuous chewing movements persisted for 16 weeks in the haloperidol alone and 3-nitropropionic acid+haloperidol group and for four weeks in the 3-nitropropionic acid alone group. Brains from each group were analysed for histopathological alterations. Bilateral striatal lesions were present only in rats with high levels of vacuous chewing movements in the 3-nitropropionic acid+haloperidol-treated rats. Nerve cell depletion and astrogliosis were prominent histopathologic features. There was selective neuronal sparing of both large- and medium-sized aspiny striatal neurons. These results suggest that mild mitochondrial impairment in combination with neuroleptics results in striatal excitotoxic neurodegeneration which may underlie the development of persistent vacuous chewing movements in rats and possibly irreversible tardive dyskinesia in humans.