Effects Of Clozapine Research Articles

Research Roundup

Review finds rigorous evidence lacking for antidepressants in cancer patients Three antidepressants show efficacy in treating older‐adult population Stimulant improves executive function in study of menopausal women Study highlights metabolite's role in clozapine's effect on memory Supervised heroin injection may work for treatment‐refractory cases

Clozapine reconstructed: Haloperidol's ability to reduce alcohol intake in the Syrian golden hamster can be enhanced through noradrenergic modulation by desipramine and idazoxan

BackgroundAlcohol use disorder commonly occurs in patients with schizophrenia. Most antipsychotic drugs do not lessen alcohol use; although the atypical antipsychotic clozapine has been shown to reduce alcohol use in patients with schizophrenia, its toxicity severely limits its use in patients. With an eye toward creation of a safer clozapine-like drug, we have investigated the pharmacological basis of the clozapine's effects on alcohol drinking in the Syrian golden hamster. In this animal, as in patients with schizophrenia, clozapine reduces alcohol drinking while the typical antipsychotic haloperidol does not. We have suggested that clozapine decreases alcohol drinking due to its weak dopamine D2 receptor blockade, its potent norepinephrine α-2 receptor antagonism, as well as its ability to elevate plasma norepinephrine. MethodsWe recreated a clozapine-like drug to reduce alcohol drinking in the Syrian golden hamster by combining low dose haloperidol with a norepinephrine α-2 receptor antagonist, idazoxan, and a norepinephrine reuptake inhibitor, desipramine. Hamsters were given free access to water and alcohol (15% v/v) and were treated daily with each drug or with the three-drug combination for 23 days. ResultsThe drug combination reduced alcohol drinking and preference significantly as compared to vehicle or to haloperidol, idazoxan or desipramine, while not altering food-intake or body-weight. ConclusionThese findings suggest that that haloperidol, which does not reduce alcohol drinking in patients with schizophrenia or the hamster, if combined with idazoxan and desipramine (producing a drug combination that mimics aspects of clozapine's pharmacology) is able to reduce alcohol drinking in the hamster.

Clozapine induces chloride channel-4 expression through PKA activation and modulates CDK5 expression in SH-SY5Y and U87 cells.

Second-generation antipsychotic drugs, such as clozapine, were reported to enhance neurite outgrowth by nerve growth factor in PC12 cells. The authors previously showed that chloride channel 4 (CLC-4) is responsible for nerve growth factor-induced neurite outgrowth in neuronal cells. In this study, we examined whether clozapine induces CLC-4 in neuroblastoma and glioma cells. The effect of clozapine on CLC-4 expression was examined in neuroblastoma (SH-SY5Y) and glioma (U87) cells. To investigate the signaling pathway responsible for clozapine-induced CLC-4 expression, the phosphorylation of cAMP response element-binding protein (CREB), which binds CRE in the promoter of the human CLC-4 gene, was examined. To identify the target of clozapine induced CLC-4, CLC-4 siRNA was introduced to neuroblastoma and glioma cells for functional knockdown. We observed that clozapine increased CLC-4 expression in both SH-SY5Y and U87 cells. Clozapine induced CREB phosphorylation, but in the presence of inhibitor of protein kinase A (an upstream kinase of CREB) clozapine-induced CLC-4 expression was suppressed. Finally, we found that CLC-4 knockdown suppressed clozapine-induced cyclin-dependent kinase 5 (CDK5) expression in SH-SY5Y and U-87 cells suggesting CDK5 as potential molecular target of clozapine induced CLC-4 expression. The results of the present study suggest that clozapine's therapeutic effect may include the induction of CLC-4 which is dependent on CREB activation via PKA. We also found that functional knockdown of CLC-4 resulted in reduction of CDK5 expression, which may also be implicated in clozapine's therapeutic effect.

Prediction of brain clozapine and norclozapine concentrations in humans from a scaled pharmacokinetic model for rat brain and plasma pharmacokinetics.

BackgroundClozapine is highly effective in treatment-resistant schizophrenia, although, there remains significant variability in the response to this drug. To better understand this variability, the objective of this study was to predict brain extracellular fluid (ECF) concentrations and receptor occupancy of clozapine and norclozapine in human central nervous system by translating plasma and brain ECF pharmacokinetic (PK) relationships in the rat and coupling these with known human disposition of clozapine in the plasma.MethodsUnbound concentrations of clozapine and norclozapine were measured in rat brain ECF using quantitative microdialysis after subcutaneous administration of a 10 mg/kg single dose of clozapine or norclozapine. These data were linked with plasma concentrations obtained in the same rats to develop a plasma–brain ECF compartmental model. Parameters describing brain ECF disposition were then allometrically scaled and linked with published human plasma PK to predict human ECF concentrations. Subsequently, prediction of human receptor occupancy at several CNS receptors was based on an effect model that related the predicted ECF concentrations to published concentration-driven receptor occupancy parameters.ResultsA one compartment model with first order absorption and elimination best described clozapine and norclozapine plasma concentrations in rats. A delay in the transfer of clozapine and norclozapine from plasma to the brain ECF compartment was captured using a transit compartment model approach. Human clozapine and norclozapine concentrations in brain ECF were simulated, and from these the median percentage of receptor occupancy of dopamine-2, serotonin-2A, muscarinic-1, alpha-1 adrenergic, alpha-2 adrenergic and histamine-1 for clozapine, and dopamine-2 for norclozapine were consistent with values reported in the literature.ConclusionsA PK model that relates clozapine and norclozapine disposition in rat plasma and brain, including blood–brain barrier transport, was developed. Using allometry and published human plasma PK, the model was successfully translated to predict clozapine and norclozapine concentrations and accordant receptor occupancy of both agents in human brain. These predicted exposure and occupancy measures at several receptors that bind clozapine may be employed to extend our understanding of clozapine’s complex behavioral effects in humans.Electronic supplementary materialThe online version of this article (doi:10.1186/1479-5876-12-203) contains supplementary material, which is available to authorized users.

Protein kinase cAMP-dependent regulatory type II beta (PRKAR2B) gene variants in antipsychotic-induced weight gain.

Antipsychotics are effective in treating schizophrenia symptoms. However, the use of clozapine and olanzapine in particular are associated with significant weight gain. Mouse and human studies suggest that the protein kinase cAMP-dependent regulatory type II beta (PRKAR2B) gene may be involved in energy metabolism, and there is evidence that it is associated with clozapine's effects on triglyceride levels. We aimed at assessing PRKAR2B's role in antipsychotic-induced weight gain in schizophrenia patients. DNA samples from adult schizophrenia or schizoaffective disorder patients of mixed ancestry were genotyped, and weight gain was assessed. We analyzed 16 tag single-nucleotide polymorphisms across the PRKAR2B gene in a Caucasian subset treated either with clozapine or olanzapine (N = 99). Linear regression based on an additive model was performed with the inclusion of relevant covariates. Normalized per cent weight change was analyzed, revealing that patients with the minor allele at rs9656135 had a mean weight increase of 4.1%, whereas patients without this allele had an increase of 3.4%. This association is not significant after correcting for multiple testing. Because of limited power, PRKAR2B's role in antipsychotic-induced weight gain is unclear, but biological evidence suggests that PRKAR2B may be involved. Further research in larger sample sizes is warranted.

Transient Receptor Potential Melastatin (TRPM) Channels Mediate Clozapine-induced Phenotypes in Caenorhabditis elegans

The molecular mechanisms of action of antipsychotic drugs (APDs) are not fully understood. Here, we characterize phenotypes of missense and knockout mutations in the Caenorhabditis elegans transient receptor potential melastatin (TRPM) channel ortholog gtl-2, a candidate APD target identified in a genome-wide RNAi (RNA interference) screen for Suppressors of Clozapine-induced Larval Arrest (scla genes). We then employ the developmental phenotypes of gtl-2(lf) mutants to validate our previous gtl-2(RNAi) result. GTL-2 acts in the excretory canal cell to regulate Mg2+ homeostasis. Using exc (excretory canal abnormal) gene mutants, we demonstrate that excretory canal cell function is necessary for clozapine-induced developmental delay and lethality. Moreover, cell-specific promoter-driven expression studies reveal that GTL-2 function in the excretory canal cell is important for its role in the SCLA phenotype. We then investigate the mechanism by which GTL-2 function in the excretory canal cell impacts clozapine-induced phenotypes. gtl-2(lf) mutations cause hypermagnesemia, and we show that exposure of the wild-type strain to high Mg2+ phenocopies gtl-2(lf) with respect to suppression of clozapine-induced developmental delay and lethality. Our results suggest that GTL-2 TRPM channel function in the excretory canal cell is important for clozapine's developmental effects. TRP channels are expressed in mammalian brain and are implicated in the pathogenesis of mental illnesses but have not been previously implicated in APD action.

Safety of long-term clozapine administration. Frequency of cardiomyopathy and hyponatraemia: Two cross-sectional, naturalistic studies

The antipsychotic drug (APD) clozapine (CLZ) is under-prescribed because of concerns about its safety. We evaluated in separate protocols the frequency of cardiomyopathy and hyponatraemia, which are adverse drug effects, where few comparative studies are available. Cross-sectional studies in subjects treated for at least 3 consecutive months with the same drug were conducted. Cardiomyopathy: Patients undergoing treatment either with CLZ (n = 125) or with other typical or atypical APDs (n = 59) were examined by a cardiologist who also recorded echocardiograms and electrocardiograms in order to diagnose cardiomyopathy. Hyponatraemia: Fasting sodium levels were assessed in patients receiving any of the following treatments: CLZ (n = 88), other atypical APDs (n = 61), typical APDs (n = 23), typical + atypical APDs (n = 11), and other drugs/drug-free (n = 36). Cardiomyopathy: No case of cardiomyopathy was detected. The frequency of abnormal ventricular ejection fraction (< 55%) was similar in both treatment groups (p = 1). Hyponatraemia: The frequency of hyponatraemia (percentage; 95% CI) was: CLZ (3.4%; -0.7, 7.1); other atypical APDs (4.9%; -0.5, 10.3); typical APDs (26.1%; 8.2, 44.0); typical + atypical APDs (9.1%; -7.8, 26.0); other drugs/drug-free (0%). None of the CLZ hyponatraemia subjects were on monotherapy. Our results are at odds with previous studies of CLZ-associated cardiomyopathy. However, they must be compared to further cross-sectional or prospective studies because most published data come from either case reports or pharmacovigilance systems. The frequency of hyponatraemia during CLZ administration was similar to that observed with other atypical APDs, and it was significantly lower than that recorded with typical agents. These results, along with numerous case reports on the effects of CLZ in patients with polydipsia and water intoxication, point to a safe or even positive profile of CLZ on electrolytic regulation.

Efficacy of pimozide augmentation for clozapine partial responders with schizophrenia

IntroductionA substantial number of patients with treatment-resistant schizophrenia respond only partially to clozapine. Therefore, it has been common practice to use augmentation strategies to maximize clozapine's effect. But the efficacy of this strategy remains poorly established. We have conducted a randomized double-blind placebo controlled clinical trial in patients with schizophrenia currently receiving clozapine with partial response, and tested the efficacy of pimozide augmentation on positive and negative symptoms and also on neurocognitive measures. MethodsThirty-two outpatients enrolled in the clinical trial and 28 completed. Patients with adequate blood levels of clozapine were randomized to pimozide vs placebo and participated in the trial for 12weeks receiving monthly assessments for Brief Psychiatric Rating Scale (BPRS) and Schedule for Assessment of Negative Symptoms (SANS), and weekly assessments for electrocardiogram (EKG), and side effects. Neurocognitive tests measuring verbal fluency, working memory, motor and attention/executive function were obtained at study entry and end of the trial. ResultsWe found no significant effect of pimozide on BPRS total, psychosis and depression subscale items, SANS scores or QTc interval. Neurocognitive measures did not show significant improvement either. DiscussionIn this well controlled clinical trial of patients with treatment-resistant schizophrenia currently receiving clozapine, pimozide augmentation was not an effective strategy to maximize the benefit for better control of positive and negative symptoms or improving neurocognitive function.

Clozapine-Induced Locomotor Suppression is Mediated by 5-HT2A Receptors in the Forebrain

The need for safer, more effective therapeutics for the treatment of schizophrenia is widely acknowledged. To optimally target novel pharmacotherapies, in addition to establishing the mechanisms responsible for the beneficial effects of antipsychotics, the pathways underlying the most severe side effects must also be elucidated. Here we investigate the role of serotonin 2A (5-HT(2A)), serotonin 2C (5-HT(2C)), and dopamine 2 receptors (D₂) in mediating adverse effects associated with canonical first- and second-generation antipsychotic drugs in mice. Wild-type (WT) and 5-HT(2A) knockout (KO) mice treated with haloperidol, clozapine, and risperidone were assessed for locomotor activity and catalepsy. WT mice showed a marked reduction in locomotor activity following acute administration of haloperidol and high-dose risperidone, which was most likely secondary to the severe catalepsy caused by these compounds. Clozapine also dramatically reduced locomotor activity, but in the absence of catalepsy. Interestingly, 5-HT(2A) KO mice were cataleptic following haloperidol and risperidone, but did not respond to clozapine's locomotor-suppressing effects. Restoration of 5-HT(2A) expression to cortical glutamatergic neurons re-instated the locomotor-suppressing effects of clozapine in the open field. In sum, we confirm that haloperidol and risperidone caused catalepsy in rodents, driven by strong antagonism of D₂. We also demonstrate that clozapine decreases locomotor activity in a 5-HT(2A)-dependent manner, in the absence of catalepsy. Moreover, we show that it is the cortical population of 5-HT(2A) that mediate the locomotor-suppressing effects of clozapine.

Clozapine decreases exploratory activity and increases anxiety-like behaviour in the Wistar–Kyoto rat but not the spontaneously hypertensive rat model of attention-deficit/hyperactivity disorder

The spontaneously hypertensive rat (SHR) is the most widely used animal model of ADHD. SHR has been found to have increased glutamate-stimulated noradrenaline release from varicosities in several brain areas. Besides its effects on dopamine D4 receptors, clozapine, an atypical antipsychotic with antagonistic effects on α1-adrenoceptors, may reduce activation of α1-adrenoceptors in SHR and thereby attenuate their hyperactivity. The aims of the study were to determine the effect of clozapine (post-natal day (P) 21–P35, 10mg/kg/day) on SHR and Wistar-Kyoto (WKY), SHR's normotensive control, and a standard laboratory strain, Sprague Dawley (SD). Rat behaviour was assessed in the open field (P32), novel object (P33) and elevated plus maze (P34) tests that measured locomotor and anxiety-related behaviour. An in vitro superfusion technique was used to measure [3H]noradrenaline release in prefrontal cortex (PFC) and hippocampal slices (P35 or P36). Clozapine decreased exploratory activity in WKY, consistent with antagonism of dopamine D4 and α1-adrenoceptors reducing the behavioural response to novelty. Clozapine also increased anxiety-related behaviour of WKY. However, clozapine did not affect SHR, suggesting that genetic predisposition may play a role in determining clozapine's behavioural effects. WKY have been shown to have higher levels of dopamine D4 receptor expression in the PFC than SHR, which may be a reason for their elevated response to clozapine. SHR released more [3H]noradrenaline from PFC and hippocampal slices in response to glutamate- and elevated potassium-stimulation, compared to WKY and SD rats. However clozapine treatment did not affect glutamate-, GABA- or depolarization-evoked release of [3H]noradrenaline.

Clozapine is gold standard, but questions remain

In their recent publication, Frogley and colleagues have reviewed the evidence indicating that clozapine treatment reduces aggressive behaviour in patients with schizophrenia, and perhaps with other disorders as well (Frogley et al. 2012). Although randomized controlled trials testing this anti-aggressive effect are relatively scarce, the evidence based on many studies supports it. There is general agreement on the superiority of clozapine's anti-aggressive effect in schizophrenia, as reflected for example in published expert consensus guidelines (Kane et al. 2003, p. 38) and in standard textbooks (Volavka et al. 2012). However, there are issues that are not quite as clear. Failure to respond to clozapine is one of these issues. In the general population of schizophrenia patients with treatment-resistant illness, only about 50% of patients respond to clozapine (Lieberman et al. 1994). The proportion of responders to clozapine in the treatment of aggression in schizophrenia has not been reliably established, but it is clear that not all patients will respond. The data published by Krakowski et al. (2006) probably represent the most robust support for the anti-aggressive superiority of clozapine over other antipsychotics in schizophrenia. The statistical analyses used in that paper (Krakowski et al. 2006) were not designed to define the outcome in dichotomous terms (response vs. non-response). However, the published interquartile ranges strongly suggest that non-responders to clozapine were present. Similar variability of response to clozapine was observed in other studies. The causes of this variability of response are not well understood. In a follow-up paper, Krakowski & Czobor (2012) demonstrated that the superiority of clozapine was probably not due to its effect on executive functioning. The variability of response is therefore apparently attributable to other factors than cognitive performance. One reason for this variability is that aggressive behaviour in schizophrenia is …

Clozapine is underutilized.

I read the piece by Wang and Li[1] with great interest. The issues surrounding the use of clozapine in China and the United States provide an interesting contrast. Wang and Li suggest that clozapine is over-utilized in China both as a first-line treatment and (in low doses) to augment other antipsychotic agents. The situation in the United States is that clozapine is grossly underutilized as a treatment for patients with refractory schizophrenia and clinically significant suicidality. Despite the evidence that 25-40% of patients with schizophrenia would be candidates for clozapine based on labeled indications, approximately 5% of patients with schizophrenia are receiving it. Clozapine was approved by the Food and Drug Administration in the United States in 1989 following a large-scale clinical trial we conducted in 1988[2] demonstrating clozapine's superiority over chlorpromazine in carefully selected treatment refractory patients who had undergone a prospective trial of high dose haloperidol in order to confirm their lack of response. Over the subsequent two decades clozapine's superiority has been confirmed in several government-funded studies.[3]–[5] Despite the introduction of other so called ‘atypical’ or second generation antipsychotics, no other compound—even those with similar chemical structures—has consistently replicated clozapine's effects. Although clozapine has been shown to be superior in patients who have failed on other medications, there is no evidence that clozapine is superior as a first-line medication. At the same time, however, it is possible that waiting until a patient fails adequate trials of three different medications is too conservative an approach; these patients may be waiting too long to try an effective treatment. Unfortunately, there is insufficient research to establish the optimum point in an individual's treatment history to introduce clozapine. It is certainly possible that the introduction of clozapine after one fully adequate failed trial of an antipsychotic medication (with confirmed adherence and therapeutic blood levels) would be sufficient. If this proved true it would be particularly valuable in the first episode of illness or in the first years after onset of illness as it would increase the likelihood of a timely treatment response. Clozapine's use has been somewhat constrained by the requirement for weekly blood monitoring in order to detect the presence of agranulocytosis. The risk of true agranulocytosis appears to have declined since the early years of clozapine use, and new methods for managing this condition has reduced fatality rates enormously. Nevertheless, the management of clozapine's side effects continues to be a challenge. Though progress is being made in identifying individuals at high risk for agranulocytosis[6] this still remains an obstacle for some physicians and patients. The risk of metabolic side effects is also very real and needs to be considered in any management plan. The appropriate or optimum dosing of clozapine also remains a challenge. Dosage patterns vary considerably from country to country. Though some studies provide guidance regarding therapeutic blood levels it is likely that there are ethnic differences in these relationships as well. Clearly, as suggested by Wang and Li,[1] more research is necessary to achieve the goals of personalized medicine in the use of a drug like clozapine, where both the potential rewards and risks are higher than usual. Some clinicians and policy makers attribute the underutilization of clozapine to its side effect profile and, therefore, patient resistance to its use. However, it is often the case that physicians project their own concerns about the possible serious side effects of clozapine onto patients and make assumptions about patients' desires without an appropriate process of shared decision-making. Moreover, many physicians in the United States and in China appear more comfortable with antipsychotic drug polypharmacy than with clozapine monotherapy, despite the fact that polypharmacy has not been adequately established as an appropriate strategy for the treatment of refractory patients. The fact that clozapine utilization varies as much as it does from country to country underscores the variety of factors that contribute to its use. Many clinicians are inadequately informed about the evidence base for the use of clozapine and about the strategies necessary for managing its potential adverse effects. Further training about clozapine is necessary. But there is also a need for research on implementation. How can the field of psychiatry better succeed at promulgating the use of evidence-based practices?

A systematic review of the evidence of clozapine's anti-aggressive effects

Reducing the risk of violent and aggressive behaviour in patients with schizophrenia remains a clinical priority. There is emerging evidence to suggest that the second-generation antipsychotic, clozapine, is effective at reducing this risk in patients with schizophrenia and some evidence to suggest that it may be best in selected patients. We conducted a systematic literature search in March 2011 of all prospective and retrospective studies, which investigated clozapine's anti-aggressive effects in a variety of mental disorders. The review identified six animal studies, four randomized controlled trials, 12 prospective non-controlled studies and 22 retrospective studies, with four case studies. We found considerable evidence in support of clozapine's ability to reduce violent and aggressive behaviour. Clozapine's anti-aggressive effect was most commonly explored in patients with schizophrenia, with less evidence available for other psychiatric disorders, including borderline personality disorder, autistic spectrum disorders, post-traumatic stress disorder, bipolar disorder and learning disability. There was mixed evidence to address the question of whether or not clozapine was any more effective than other antipsychotics. In the case of schizophrenia, there was evidence to suggest that clozapine's anti-aggressive effect was more marked particularly in those with treatment-resistant illness. Its anti-aggressive effects appeared to be 'specific', being to some extent greater than both its more general antipsychotic and sedative effects. There were significant methodological inconsistencies in the studies we identified, particularly surrounding patient recruitment criteria, the definition and measurement of violence and the lack of randomized, controlled trials. Data on therapeutic monitoring were also limited. Clozapine can reduce violence and persistent aggression in patients with schizophrenia and other psychiatric disorders. It may offer an advantage over other antipsychotics, although perhaps exclusively in the case of traditionally defined 'treatment resistance' or more broadly defined 'complex cases' with co-morbidity. Larger, randomized, blinded, controlled studies with robust characterization of participants, and standardized measures of violence and aggression are, however, needed to fully understand this link and explore the possible mechanisms.

Clozapine administration ameliorates disrupted long-range synchrony in a neurodevelopmental animal model of schizophrenia

The abnormal synchronisation of neural networks may underlie some of the deficits observed in schizophrenia. Abnormal synchronisation can be induced in animal models. We investigated whether acute clozapine treatment might function therapeutically by ameliorating the deficit in theta frequency coherence between the prefrontal cortex and the hippocampus that is induced in rats exposed to maternal immune activation (MIA)—a risk-factor for schizophrenia. Clozapine treatment increased synchrony levels to that of control animals in a dose-dependent manner. Clozapine's effect on synchrony may in part be mediated through increases in local synchrony that occurred in prefrontal cortex but not hippocampus.

P-1111 - The untrusted hero: updating safety issues and clozapine's use in the clinical setting

Recent research and guidelines’ recommendations favour clozapine use, probably more than ever, but even though most clinicians remain reluctant prescribing it. To assess the mismatch between clozapine's treatment indications and prescription rates, discuss the underlying motives for such a discrepancy and possible interventions to reduce the gap. Promote clozapine use when indicated and raise awareness of the impact in terms of patients’ health and healthcare costs. A qualitative review of the evidence on clozapine's use. The response rate to clozapine is approximately 50%, irrespective of non-response to prior treatment and has unique anti-suicidal, anti-aggressive and comorbid substance abuse properties. About one third of schizophrenia patients have treatment-resistant schizophrenia, however only one third are prescribed clozapine and its initiation is 5 years delayed. Doctor's reluctance in prescribing clozapine may be related to its perceptions regarding clozapine's serious side effects and patient's satisfaction. Nevertheless, monitoring serious side effects such as agranulocytosis considerably reduces fatalities and one year after treatment initiation such risk is comparable to other drugs like haloperidol; despite feared side effects with clozapine use, studies showed that clozapine is associated to reduced premature death even compared with those not taking regular medication; most patient's claim to feel better on clozapine, prefer to remain on clozapine and express that the advantages of clozapine outweigh disadvantages. Clozapine remains the only antipsychotic licensed to treatment-resistant schizophrenia. Despite its clinical superiority, lower costs associated to treatment, patient's preferences and overestimated safety concerns, clozapine remains considerably underused.

Behavioral effects of clozapine: Involvement of trace amine pathways in C. elegans and M. musculus

Clozapine is an antipsychotic medication with superior efficacy in treatment refractory schizophrenia. The molecular basis of clozapine's therapeutic profile is not well understood. We studied behavioral effects of clozapine in Caenorhabditis elegans to identify novel pathways that modulate clozapine's biological effects. Clozapine stimulated egg laying in C. elegans in a dose-dependent manner. This effect was clozapine-specific, as it was not observed with exposure to a typical antipsychotic, haloperidol or an atypical antipsychotic, olanzapine. A candidate gene screen of biogenic amine neurotransmitter systems identified signaling pathways that mediate this clozapine-specific effect on egg laying. Specifically, we found that clozapine-induced increase in egg laying requires tyramine biosynthesis. To test the implications of this finding across species, we explored whether trace amine systems modulate clozapine's behavioral effects in mammals by studying trace amine-associated receptor 1 (TAAR1) knockout mice. Clozapine increased prepulse inhibition (PPI) in wild-type mice. This increase in PPI was abrogated in TAAR1 knockout mice, implicating TAAR1 in clozapine-induced PPI enhancement. In transfected mammalian cell lines, we found no TAAR activation by antipsychotics, suggesting that modulation of trace amine signaling in mice does not occur directly at the receptor itself. In summary, we report a heretofore-unknown role for trace amine systems in clozapine-mediated effects across two species: C. elegans and mice.

Clozapine and sulpiride but not haloperidol or olanzapine activate brain DNA demethylation

Cortical GABAergic dysfunction, a hallmark of both schizophrenia (SZ) and bipolar (BP) disorder pathophysiologies may relate to the hypermethylation of GABAergic gene promoters (i.e., reelin and GAD67). Benefits elicited by a combination of atypical antipsychotics with valproate (VPA) (a histone deacetylase inhibitor that may also activate brain DNA demethylation) in SZ or BP disorder treatment prompted us to investigate whether the beneficial action of this association depends on induction of a putative DNA demethylase activity. To monitor this activity, we measured the ratio of 5-methyl cytosine to unmethylated cytosine in reelin and GAD67 promoters in the mouse frontal cortex and striatum. We compared normal mice with mice pretreated with l-methionine (5.2 mmol/kg s.c. twice a day for 7 days) to hypermethylate promoters, including reelin and GAD67. Clinically relevant doses of clozapine (CLZ) (3.8 to 15 micromol/kg twice a day s.c. for 3 days) and sulpiride (SULP) (12.5 to 50 micromol/kg twice a day for 3 days) but not clinically relevant doses of haloperidol (HAL) (1.3 to 4 micromol/kg twice a day s.c. for 3 days) or olanzapine (OLZ) (4 to 15 micromol/kg twice a day for 3 days) exhibited dose-related increases in the cortical and striatal demethylation of hypermethylated reelin and GAD67 promoters. These effects of CLZ and SULP were dramatically potentiated by a clinically relevant VPA dose (0.5 mmol/kg twice a day for 3 days). By activating a DNA demethylase, the association of CLZ or SULP with VPA may facilitate a chromatin remodeling that normalizes the GABAergic gene expression down-regulation detected in the telencephalic regions of SZ and BP patients.

Evaluation of age and sex differences in locomotion and catalepsy during repeated administration of haloperidol and clozapine in adolescent and adult rats

Adolescence is associated with characteristic behavioral patterns as well as with substantial neuronal pruning and re-organization of the brain. Recent research has determined that the effects of various centrally active drugs differ in adolescents and adults. This study examined the motor effects of two prototypic antipsychotics in adult [>postnatal day 70 (PN70)] and adolescent (PN30–PN39) rats. Rats were injected daily with saline, 0.3 mg/kg haloperidol, or 10 mg/kg clozapine for 10 days and activity and catalepsy were measured. Adolescents of both sexes were less sensitive to the cataleptic effects of haloperidol than were adults. Male adolescents were also less sensitive to the cataleptic effects of clozapine, although this difference was transitory. In contrast, female adults showed decreased sensitivity to clozapine's effects, differing from all other groups. These results suggest that adolescents of both sexes may be less sensitive to the extrapyramidal motor effects of haloperidol. Translational implications of the clozapine results are less clear; however, results suggest that developmental differences in neurochemical systems affected by clozapine that are also related to motor behavior may play a role. These results also emphasize the importance of age and sex as determinants of the pharmacological effects of these antipsychotics.

Special Section on Implications of CATIE: What CATIE Did: Some Thoughts on Implications Deep and Wide

Special Section on Implications of CATIE: What CATIE Did: Some Thoughts on Implications Deep and Wide

Increase in extracellular dopamine levels during clozapine-induced potentiation in the hippocampal dentate gyrus of chronically prepared rabbits

We previously found that 20 mg/kg clozapine i.p. potentiated the excitatory synaptic responses elicited in the dentate gyrus by single electrical stimulation of the perforant path in chronically prepared rabbits. We called this phenomenon clozapine-induced potentiation and proved that it was an NMDA receptor-mediated event. This potentiation is presumably related to clozapine's clinical effect on negative symptoms and cognitive dysfunctions in schizophrenia. In the present study, to investigate the mechanisms underlying clozapine-induced potentiation, we examined whether extracellular dopamine and 5-HT levels changed during the potentiation by using a microdialysis technique in the dentate gyrus. The extracellular concentrations of dopamine and 5-HT levels were measured every 5 min during all experiments. Extracellular 5-HT levels did not change, but dopamine levels eventually increased significantly during clozapine-induced potentiation. The increase in the dopamine levels occurred almost simultaneously with the induction of clozapine-induced potentiation. These results suggest that clozapine-induced potentiation is at least partly attributable to a dopamine-mediated potentiation of excitatory synaptic transmission. The present study implies that such phenomena occur also in the perforant path-dentate gyrus pathway.