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

Continuous oral olanzapine or clozapine treatment initiated in adolescence has differential short- and long-term impacts on antipsychotic sensitivity than those initiated in adulthood

One of the major discoveries in recent research on antipsychotic drugs is that antipsychotic treatment in adolescence could induce robust long-term alterations in antipsychotic sensitivity that persist into adulthood. These long-term impacts are likely influenced by various factors, including the "diseased" state of animals, sex, type of drugs, mode of drug administration, and age of treatment onset. In this study we compared the short- and long-term behavioral effects of 21-day continuous oral olanzapine (7.5 mg/kg/day) or clozapine (30.0 mg/kg/day) administration in heathy or maternal immune activated adolescent (33-53 days old) or adult (80-100 days old) rats of both sexes. We used a conditioned avoidance response model to assess the drug-induced alterations in antipsychotic sensitivity. Here, we report that while under the chronic drug treatment period, olanzapine progressively increased its suppression of avoidance responding over time, especially when treatment was initiated in adulthood. Clozapine's suppression depended on the age of drug exposure, with treatment initiated in adulthood showing a suppression while that initiated in adolescent did not. After a 17-day drug-free interval, in a drug challenge test, olanzapine treatment initiated in adolescence caused a decrease in drug sensitivity, as reflected by less avoidance suppression (a tolerance effect); whereas that initiated in adulthood appeared to cause an increase (more avoidance suppression, a sensitization effect). Clozapine treatments initiated in both adolescence and adulthood caused a similar tolerance effect. Our findings indicate that the same chronic antipsychotic treatment regimen initiated in adolescence or adulthood can have differential short- and long-term impacts on drug sensitivity.

Lower levels of tubulin alpha 1b in the frontal pole in schizophrenia supports a role for changed cytoskeletal dynamics in the aetiology of the disorder

Our transcriptomic study suggested there were markedly lower levels of tubulin alpha 1b (TUBA1B) expression in BA 10, but not BA 9, from patients with schizophrenia. We now use Western blotting to compare levels of TUBA1B protein in BA 9 and 10 from patients with schizophrenia and BA 10 from patients with mood disorders to controls as well as in the frontal cortex from rats after treatment with haloperidol, chlorpromazine or vehicle for 28 days. Levels of TUBA1B were significantly lower (- 18.6%) in BA 10, but not BA 9, from patients with schizophrenia. Levels of TUBA1B did not differ significantly from controls in BA 10 from patients with mood disorders or in the cortex of rats after antipsychotic drug treatments. Levels of TUBA1B were significantly lower (- 30%) in BA 10 from patients with schizophrenia who were not being treated with antipsychotic drugs close to death compared to those who were treated close to death. These data suggest that lower levels of TUBA1B, a cytoskeletal protein, in BA 10 from patients with schizophrenia are not a simple drug effect and therefore add to the hypothesis that a breakdown in cytoskeletal homoeostasis may be contributing to the genesis of the symptoms of the disorder.

Cortical expression of the RAPGEF1 gene in schizophrenia: investigating regional differences and suicide

Rap guanine nucleotide exchange factor 1 (RAPGEF1) is involved in cell adhesion and neuronal migration. Previously we found lower RAPGEF1 mRNA levels in Brodmann's area (BA) 9 in subjects with schizophrenia compared to controls. This study aimed to determine whether RAPGEF1 expression was altered in other brain regions implicated in schizophrenia and whether this was associated with suicide. Using qPCR, we measured the levels of RAPGEF1 in post-mortem BA 8 and 44 from 27 subjects with schizophrenia and 26 non-psychiatric control subjects. To address the effect of antipsychotic treatments, Rapgef1 mRNA levels were measured in the cortex from rats treated with typical antipsychotic drugs. There was no difference in RAPGEF1 normalised relative expression levels in BA 8 or 44. However, in BA 8, schizophrenia subjects had higher raw Ct RAPGEF1 levels compared to controls. There were higher RAPGEF1 levels in suicide completers compared to non-suicide schizophrenia subjects in BA 8. Rapgef1 expression levels in the rat cortex did not vary with antipsychotic treatment. Our findings suggest changes in RAPGEF1 expression may be limited to the dorsolateral prefrontal cortex from subjects with schizophrenia. Further investigation of the function of RAPGEF1 may lead to a greater understanding of the pathophysiology of schizophrenia.

Reversal of social deficits by subchronic oxytocin in two autism mouse models

Social deficits are a hallmark feature of autism spectrum disorder (ASD) and related developmental syndromes. Although there is no standard treatment for social dysfunction, clinical studies have identified oxytocin as a potential therapeutic with prosocial efficacy. We have previously reported that peripheral oxytocin treatment can increase sociability and ameliorate repetitive stereotypy in adolescent mice from the C58/J model of ASD-like behavior. In the present study, we determined that prosocial oxytocin effects were not limited to the adolescent period, since C58/J mice, tested in adulthood, demonstrated significant social preference up to 2 weeks following subchronic oxytocin treatment. Oxytocin was also evaluated in adult mice with underexpression of the N-methyl-d-aspartate receptor NR1 subunit (encoded by Grin1), a genetic model of autism- and schizophrenia-like behavior. Subchronic oxytocin had striking prosocial efficacy in male Grin1 knockdown mice; in contrast, chronic regimens with clozapine (66 mg/kg/day) or risperidone (2 mg/kg/day) failed to reverse deficits in sociability. Neither the subchronic oxytocin regimen, nor chronic treatment with clozapine or risperidone, reversed impaired prepulse inhibition in the Grin1 knockdown mice. Overall, these studies demonstrate oxytocin can enhance sociability in mouse models with divergent genotypes and behavioral profiles, adding to the evidence that this neurohormone could have therapeutic prosocial efficacy across a spectrum of developmental disorders.

Tyrosine hydroxylase localization in the nucleus accumbens in schizophrenia

The nucleus accumbens (NAcc) has been implicated in schizophrenia (SZ) pathology, based on antipsychotic action therein. However, recent imaging studies suggest that the NAcc may not be a locus of dopamine dysregulation in SZ. This study examined postmortem human tissue to determine if abnormalities are present in dopamine synthesis in the NAcc in SZ. We compared the immunohistochemical localization of tyrosine hydroxylase (TH), the rate-limiting synthesizing enzyme of dopamine, in postmortem tissue from SZ subjects and demographically matched controls. To study the effects of chronic antipsychotic drug (APD) treatment on TH immunolabeling in the NAcc, rats were treated for 6 months with haloperidol or olanzapine. In the NAcc, TH immunolabeling was similar in control and SZ subjects, in both the core and shell. Rats had similar TH optical density levels across treatment groups in both the core and shell. Similar levels of TH suggest DA synthesis may be normal. These findings provide further insight into the role of the NAcc in SZ.

Antipsychotic-induced metabolic effects in the female rat: Direct comparison between long-acting injections of risperidone and olanzapine

Several antipsychotics have well-known adverse metabolic effects. Studies uncovering molecular mechanisms of such drugs in patients are challenging due to high dropout rates, previous use of antipsychotics and restricted availability of biological samples. Rat experiments, where previously unexposed animals are treated with antipsychotics, allow for direct comparison of different drugs, but have been hampered by the short half-life of antipsychotics in rodents. The use of long-acting formulations of antipsychotics could significantly increase the value of rodent models in the molecular characterization of therapeutic and adverse effects of these agents. However, as long-acting formulations have rarely been used in rodents, there is a need to characterize the basic metabolic phenotype of different antipsychotics. Using long-acting olanzapine injections as a positive control, the metabolic effects of intramuscular long-acting risperidone in female rats were investigated for the first time. Like olanzapine, risperidone induced rapid, significant hyperphagia and weight gain, with concomitant increase in several plasma lipid species. Both drugs also induced weight-independent upregulation of several genes encoding enzymes involved in lipogenesis, but this activation was not confirmed at the protein level. Our findings shed light on the role of drug administration, drug dose and nutritional status in the development of rodent models for adverse metabolic effects of antipsychotic agents.

Assessment of cytochrome C oxidase dysfunction in the substantia nigra/ventral tegmental area in schizophrenia

Perturbations in metabolism are a well-documented but complex facet of schizophrenia pathology. Optimal cellular performance requires the proper functioning of the electron transport chain, which is constituted by four enzymes located within the inner membrane of mitochondria. These enzymes create a proton gradient that is used to power the enzyme ATP synthase, producing ATP, which is crucial for the maintenance of cellular functioning. Anomalies in a single enzyme of the electron transport chain are sufficient to cause disruption of cellular metabolism. The last of these complexes is the cytochrome c oxidase (COX) enzyme, which is composed of thirteen different subunits. COX is a major site for oxidative phosphorylation, and anomalies in this enzyme are one of the most frequent causes of mitochondrial pathology. The objective of the present report was to assess if metabolic anomalies linked to COX dysfunction may contribute to substantia nigra/ventral tegmental area (SN/VTA) pathology in schizophrenia. We tested COX activity in postmortem SN/VTA from schizophrenia and non-psychiatric controls. We also tested the protein expression of key subunits for the assembly and activity of the enzyme, and the effect of antipsychotic medication on subunit expression. COX activity was not significantly different between schizophrenia and non-psychiatric controls. However, we found significant decreases in the expression of subunits II and IV-I of COX in schizophrenia. Interestingly, these decreases were observed in samples containing the entire rostro-caudal extent of the SN/VTA, while no significant differences were observed for samples containing only mid-caudal regions of the SN/VTA. Finally, rats chronically treated with antipsychotic drugs did not show significant changes in COX subunit expression. These findings suggest that COX subunit expression may be compromised in specific sub-regions of the SN/VTA (i.e. rostral regions), which may lead to a faulty assembly of the enzyme and a greater vulnerability to metabolic insult.

Dopamine denervation of the prefrontal cortex increases expression of the astrocytic glutamate transporter GLT-1

Both dopamine and glutamate are critically involved in cognitive processes such as working memory. Astrocytes, which express dopamine receptors, are essential elements in the termination of glutamatergic signaling: the astrocytic glutamate transporter GLT-1 is responsible for > 90% of cortical glutamate uptake. The effect of dopamine depletion on glutamate transporters in the prefrontal cortex (PFC) remains unknown. In an effort to determine if astrocytes are a locus of cortical dopamine-glutamate interactions, we examined the effects of chronic dopamine denervation on PFC protein and mRNA levels of glutamate transporters. PFC dopamine denervation elicited a marked increase in GLT-1 protein levels, but had no effect on levels of other glutamate transporters; high-affinity glutamate transport was positively correlated with the extent of dopamine depletion. GLT-1 gene expression was not altered. Our data suggest that dopamine depletion may lead to post-translational modifications that result in increased expression and activity of GLT-1 in PFC astrocytes. The glutamate transporter GLT-1 is expressed by astrocytes, which also express dopamine receptors. Regulation of prefrontal cortical (PFC) GLT-1 potentially offers a novel treatment approach to the cognitive deficits of schizophrenia. Partial PFC dopamine deafferentation increased membrane expression of GLT-1 protein and glutamate uptake, but did not alter levels of the other two neocortical glutamate transporters, GLAST and EAAC1.

Olanzapine depot formulation in rat: a step forward in modelling antipsychotic-induced metabolic adverse effects

Rats are used as animal models in the study of antipsychotic-induced metabolic adverse effects, with oral drug administration yielding hyperphagia, weight gain and, in some cases, lipogenic effects. However, the rapid half-life of these drugs in rats, in combination with development of drug tolerance after a few weeks of treatment, has limited the validity of the model. In order to prevent fluctuating drug serum concentrations seen with daily repeated administrations, we injected female rats with a single intramuscular dose of long-acting olanzapine formulation. The olanzapine depot injection yielded plasma olanzapine concentrations in the range of those achieved in patients, and induced changes in metabolic parameters similar to those previously observed with oral administration, including increased food intake, weight gain and elevated plasma triglycerides. Moreover, the sensitivity to olanzapine was maintained beyond the 2-3 wk of weight gain observed with oral administration. In a separate olanzapine depot experiment, we aimed to clarify the role of hypothalamic AMP-activated protein kinase (AMPK) in olanzapine-induced weight gain, which has been subject to debate. Adenovirus-mediated inhibition of AMPK was performed in the arcuate (ARC) or the ventromedial hypothalamic (VMH) nuclei in female rats, with subsequent injection of olanzapine depot solution. Inhibition of AMPK in the ARC, but not in the VMH, attenuated the weight-inducing effect of olanzapine, suggesting an important role for ARC-specific AMPK activation in mediating the orexigenic potential of olanzapine. Taken together, olanzapine depot formulation provides an improved mode of drug administration, preventing fluctuating plasma concentrations, reducing handling stress and opening up possibilities to perform complex mechanistic studies.

Olanzapine treatment of adolescent rats alters adult reward behaviour and nucleus accumbens function

Antipsychotic drugs are increasingly used in children and adolescents to treat a variety of psychiatric disorders. However, little is known about the long-term effects of early life antipsychotic drug (APD) treatment. Most APDs are potent antagonists or partial agonists of dopamine (DA) D₂ receptors; atypical APDs also have multiple serotonergic activities. DA and serotonin regulate many neurodevelopmental processes. Thus, early life APD treatment can, potentially, perturb these processes, causing long-term behavioural and neurobiological sequelae. We treated adolescent, male rats with olanzapine (Ola) on post-natal days 28-49, under dosing conditions that approximate those employed therapeutically in humans. As adults, they exhibited enhanced conditioned place preference for amphetamine, as compared to vehicle-treated rats. In the nucleus accumbens core, DA D₁ receptor binding was reduced, D₂ binding was increased and DA release evoked by electrical stimulation of the ventral tegmental area was reduced. Thus, adolescent Ola treatment enduringly alters a key behavioural response to rewarding stimuli and modifies DAergic neurotransmission in the nucleus accumbens. The persistence of these changes suggests that even limited periods of early life Ola treatment may induce enduring changes in other reward-related behaviours and in behavioural and neurobiological responses to therapeutic and illicit psychotropic drugs. These results underscore the importance of improved understanding of the enduring sequelae of paediatric APD treatment as a basis for weighing the benefits and risks of adolescent APD therapy, especially prophylactic treatment in high-risk, asymptomatic patients.

Olanzapine treatment of adolescent rats causes enduring specific memory impairments and alters cortical development and function

Antipsychotic drugs are increasingly used in children and adolescents to treat a variety of psychiatric disorders. However, little is known about the long-term effects of early life antipsychotic drug treatment. Most antipsychotic drugs are potent antagonists or partial agonists of dopamine D2 receptors; atypical antipsychotic drugs also antagonize type 2A serotonin receptors. Dopamine and serotonin regulate many neurodevelopmental processes. Thus, early life antipsychotic drug treatment can, potentially, perturb these processes, causing long-term behavioral- and neurobiological impairments. Here, we treated adolescent, male rats with olanzapine on post-natal days 28-49. As adults, they exhibited impaired working memory, but normal spatial memory, as compared to vehicle-treated control rats. They also showed a deficit in extinction of fear conditioning. Measures of motor activity and skill, habituation to an open field, and affect were normal. In the orbital- and medial prefrontal cortices, parietal cortex, nucleus accumbens core and dentate gyrus, adolescent olanzapine treatment altered the developmental dynamics and mature values of dendritic spine density in a region-specific manner. Measures of motor activity and skill, habituation to an open field, and affect were normal. In the orbital- and medial prefrontal cortices, D1 binding was reduced and binding of GABA(A) receptors with open Cl(-) channels was increased. In medial prefrontal cortex, D2 binding was also increased. The persistence of these changes underscores the importance of improved understanding of the enduring sequelae of pediatric APD treatment as a basis for weighing the benefits and risks of adolescent antipsychotic drug therapy, especially prophylactic treatment in high risk, asymptomatic patients. The long-term changes in neurotransmitter receptor binding and neural circuitry induced by adolescent APD treatment may also cause enduring changes in behavioral- and neurobiological responses to other therapeutic- or illicit psychotropic drugs.

Dopamine pathology in schizophrenia: analysis of total and phosphorylated tyrosine hydroxylase in the substantia nigra

INTRODUCTION

Despite the importance of dopamine neurotransmission in schizophrenia, very few studies have addressed anomalies in the mesencephalic dopaminergic neurons of the substantia nigra/ventral tegmental area (SN/VTA). Tyrosine hydroxylase (TH) is the rate-limiting enzyme for the production of dopamine, and a possible contributor to the anomalies in the dopaminergic neurotransmission observed in schizophrenia.

OBJECTIVES

In this study, we had three objectives: (1) Compare TH expression (mRNA and protein) in the SN/VTA of schizophrenia and control postmortem samples. (2) Assess the effect of antipsychotic medications on the expression of TH in the SN/VTA. (3) Examine possible regional differences in TH expression anomalies within the SN/VTA.

METHODS

To achieve these objectives three independent studies were conducted: (1) A pilot study to compare TH mRNA and TH protein levels in the SN/VTA of postmortem samples from schizophrenia and controls. (2) A chronic treatment study was performed in rodents to assess the effect of antipsychotic medications in TH protein levels in the SN/VTA. (3) A second postmortem study was performed to assess TH and phosphorylated TH protein levels in two types of samples: schizophrenia and control samples containing the entire rostro-caudal extent of the SN/VTA, and schizophrenia and control samples containing only mid-caudal regions of the SN/VTA.

RESULTS AND CONCLUSION

Our studies showed impairment in the dopaminergic system in schizophrenia that could be mainly (or exclusively) located in the rostral region of the SN/VTA. Our studies also showed that TH protein levels were significantly abnormal in schizophrenia, while mRNA expression levels were not affected, indicating that TH pathology in this region may occur posttranscriptionally. Lastly, our antipsychotic animal treatment study showed that TH protein levels were not significantly affected by antipsychotic treatment, indicating that these anomalies are an intrinsic pathology rather than a treatment effect.

Phencyclidine-induced loss of asymmetric spine synapses in rodent prefrontal cortex is reversed by acute and chronic treatment with olanzapine

Enduring cognitive deficits exist in schizophrenic patients, long-term abusers of phencyclidine (PCP), as well as in animal PCP models of schizophrenia. It has been suggested that cognitive performance and memory processes are coupled with remodeling of pyramidal dendritic spine synapses in prefrontal cortex (PFC), and that reduced spine density and number of spine synapses in the medial PFC of PCP-treated rats may potentially underlie, at least partially, the cognitive dysfunction previously observed in this animal model. The present data show that the decrease in number of asymmetric (excitatory) spine synapses in layer II/III of PFC, previously noted at 1-week post PCP treatment also occurs, to a lesser degree, in layer V. The decrease in the number of spine synapses in layer II/III was sustained and persisted for at least 4 weeks, paralleling the observed cognitive deficits. Both acute and chronic treatment with the atypical antipsychotic drug, olanzapine, starting at 1 week after PCP treatment at doses that restore cognitive function, reversed the asymmetric spine synapse loss in PFC of PCP-treated rats. Olanzapine had no significant effect on spine synapse number in saline-treated controls. These studies demonstrate that the effect of PCP on asymmetric spine synapse number in PFC lasts at least 4 weeks in this model. This spine synapse loss in PFC is reversed by acute treatment with olanzapine, and this reversal is maintained by chronic oral treatment, paralleling the time course of the restoration of the dopamine deficit, and normalization of cognitive function produced by olanzapine.

Long term antipsychotic treatment does not alter metabolite concentrations in rat striatum: an in vivo magnetic resonance spectroscopy study

Proton magnetic resonance spectroscopy (MRS) studies of schizophrenic patients generally reveal reduced levels of N-acetyl aspartate (NAA) when compared with healthy controls. Whether this reduction is due to the disease or to the drugs used for treatment remains an open question. Numerous human and animal studies have attempted to determine the effects of antipsychotics on NAA levels with mixed results. The majority of the animal studies were ex vivo, which may not accurately reflect the in vivo situation, and limitations of the human studies include previous or concomitant medications or other confounds. To overcome these limitations, we dosed 10 rats/group for six months via drinking water with 0.2 or 2 mg/kg/day haloperidol or 10 or 30 mg/kg/day clozapine. Control rats received unadulterated water. Proton MRS data were collected longitudinally over the six month period from a 64 μL voxel containing primarily the right striatum prior to and monthly during drug administration and used to estimate the concentrations of NAA, creatine, and choline. Ratios of NAA, choline, inositol and glutamate+glutamine to creatine were also calculated. Only the Cho/Cr ratio showed a significant time-by-treatment effect (p=0.0285). These results are in agreement with previous studies of the striatum. However, regional and disease-specific effects remain unresolved.

A murine model of atypical antipsychotic-induced weight gain and metabolic dysregulation

In comparison with conventional, first-generation antipsychotics (e.g., haloperidol), the administration of atypical antipsychotics (AAPs) has been associated with a higher risk of metabolic derangements, including body weight increase, dysregulation of glucose homeostasis, fat accumulation, and even liability to develop type II diabetes. Since this is a serious clinical problem that may be further exacerbated in overweight schizophrenics, establishing animal models of AAP-induced adverse effects may contribute to clarifying the mechanisms underlying these effects. Here we present three basic protocols by which this problem has been modeled. The three protocols differ in many aspects (routes of administration, extent of the chronic treatment, diets, and dosage regimen), and the pros and cons of each procedure are systematically detailed throughout. It should be noted that several factors (e.g., species, sex, duration, and class of AAPs) could restrict the feasibility of these models, as well as their correspondence to the clinical condition.

Evaluating early preventive antipsychotic and antidepressant drug treatment in an infection-based neurodevelopmental mouse model of schizophrenia

Current pharmacotherapy of schizophrenia remains unsatisfactory with little hope for complete functional restoration in patients once the disease has developed. A preventive approach based on intervention in the prodromal stage of the disease aiming to preserve functional integrity by halting the progress of the disease is therefore extremely attractive. Here, we investigated the effects of preventive antipsychotic or antidepressant drug treatment in a well-established neurodevelopmental mouse model of multiple schizophrenia-related abnormalities. Pregnant mice on gestation day 9 were exposed to the viral mimic polyriboinosinic-polyribocytidylic acid (2 mg/kg, intravenously) or corresponding vehicle treatment, and the resulting offspring from both prenatal treatment conditions were subjected to chronic antipsychotic (haloperidol or clozapine), antidepressant (fluoxetine), or placebo treatment during the periadolescent stage of development. The effects of the preventive pharmacotherapy on behavioral and pharmacological functions were then investigated in adulthood using paradigms relevant to schizophrenia, namely prepulse inhibition, latent inhibition, and sensitivity to psychostimulant drugs. We show that periadolescent treatment with the reference antipsychotic and antidepressant drugs can successfully block the emergence of multiple psychosis-related behavioral and pharmacological abnormalities in subjects predisposed to adult brain pathology by exposure to prenatal immune challenge. At the same time, however, our study reveals numerous negative influences of the early pharmacological intervention on normal behavioral development in control subjects. Hence, even though preventive pharmacotherapy may be beneficial in individuals with predisposition to psychosis-related brain dysfunctions, chronic antipsychotic or antidepressant drug treatment in false-positive subjects is associated with substantial risk for long-term behavioral disturbances in adulthood.

Dystrophic dendrites in prefrontal cortical pyramidal cells of dopamine D1 and D2 but not D4 receptor knockout mice

Recent data indicate that cortical dopamine denervation results in dystrophic changes in the dendrites of pyramidal cells, including decreases in dendritic spine density and length. However, it is not known if the loss of signaling through specific dopamine receptors subserves these dendritic changes. We examined the dendritic structure of layer V pyramidal cells in the prefrontal cortex of D(1), D(2), and D(4) dopamine receptor null mutant mice and their wild-type littermates. Decreased basal dendritic length and spine density were observed in the D(1) knockout mice. Similarly, a decrease in basal dendritic spine density was uncovered in the D(2) knockout mice relative to wild-type littermates. No changes in any dendritic parameter were observed in the D(4) knockout mice. These observations suggest that the dystrophic changes observed in prefrontal cortical pyramidal cell dendrites are due to loss of signaling through D(1) and possibly D(2) receptors. The current data also suggest that caution should be exercised in the interpretation of behavioral, physiological, and biochemical studies of the prefrontal cortex in dopamine receptor knockout mice.

A role for dopamine D2 receptors in reversal learning

Reversal learning has been shown to require intact serotonergic innervation of the forebrain neocortex. Whether dopamine acting through D2 receptors plays a complementary role in this anatomic area is still unclear. Here we show that mice lacking dopamine D2 receptors exhibited significantly impaired performance in the reversal learning phase of an attention-set-shifting task (ASST) and that wild type mice treated chronically with the D2-like receptor antagonist haloperidol exhibited the same cognitive deficit. The test-phase-specific deficits of D2 mutants and haloperidol-treated mice were also accompanied by deficits in the induction of expression of early growth response gene 2 (egr-2), a regulatory transcription factor previously shown to be selectively induced in the ventrolateral orbital frontal cortex and the pre- and infralimbic medial prefrontal cortex of ASST-tested mice. D2-receptor knockout mice and haloperidol-treated wild type, however, exhibited lower egr-2 expression in these anatomic regions after completion of an ASST-test phase that required reversal learning but not after completion of set-shifting phases without rule reversals. In contrast, mice treated chronically with clozapine, an atypical neuroleptic drug with lower D2-receptor affinity and broader pharmacological effects, had deficits in compound discrimination phases of the ASST, but also these deficits were accompanied by lower egr-2 expression in the same anatomic subregions. Thus, the findings indicate that egr-2 expression is a sensitive indicator of test-phase-specific performance in the ASST and that normal function of D2 receptors in subregions of the orbital frontal and the medial prefrontal cortex is required for cognitive flexibility in tests involving rule reversals.

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.