Repeated antipsychotic drug exposurein developing rats: Dopamine receptor effects

Early-life risperidone alters locomotor responses to apomorphine and quinpirole in adulthood

An escalating trend of antipsychotic drug use in children with ADHD, disruptive behavior disorder, or mood disorders has raised concerns about the impact of these drugs on brain development. Since antipsychotics chiefly target dopamine receptors, it is important to assay the function of these receptors after early-life antipsychotic administration. Using rats as a model, we examined the effects of early-life risperidone, the most prescribed antipsychotic drug in children, on locomotor responses to the dopamine D1/D2 receptor agonist, apomorphine, and the D2/D3 receptor agonist, quinpirole. Female and male Long-Evans rats received daily subcutaneous injections of risperidone (1.0 and 3.0 mg/kg) or vehicle from postnatal day 14-42. Locomotor responses to one of three doses (0.03, 0.1, and 0.3 mg/kg) of apomorphine or quinpirole were tested once a week for four weeks beginning on postnatal day 76 and 147 for each respective drug. The locomotor activity elicited by the two lower doses of apomorphine was significantly greater in adult rats, especially females, administered risperidone early in life. Adult rats administered risperidone early in life also showed more locomotor activity after the low dose of quinpirole. Overall, female rats were more sensitive to the locomotor effects of each agonist. In a separate group of rats administered risperidone early in life, autoradiography of forebrain D2 receptors at postnatal day 62 revealed a modest increase in D2 receptor density in the medial caudate. These results provide evidence that early-life risperidone administration can produce long-lasting changes in dopamine receptor function and density.

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

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

Modulation by chronic antipsychotic administration of PKA- and GSK3β-mediated pathways and the NMDA receptor in rat ventral midbrain

RATIONALE

Antipsychotics exert therapeutic effects by modulating various cellular signalling pathways and several types of receptors, including PKA- and GSK3β-mediated signalling pathways, and NMDA receptors. The ventral midbrain, mainly containing the ventral tegmental area (VTA) and substantia nigra (SN), are the nuclei with dopamine origins in the brain, which are also involved in the actions of antipsychotics. Whether antipsychotics can modulate these cellular pathways in the ventral midbrain is unknown.

OBJECTIVE

This study aims to investigate the effects of antipsychotics, including aripiprazole (a dopamine D₂ receptor (D₂R) partial agonist), bifeprunox (a D₂R partial agonist), and haloperidol (a D₂R antagonist) on the PKA- and GSK3β-mediated pathways and NMDA receptors in the ventral midbrain.

METHODS

Male rats were orally administered aripiprazole (0.75 mg/kg, t.i.d. (ter in die)), bifeprunox (0.8 mg/kg, t.i.d.), haloperidol (0.1 mg/kg, t.i.d.) or vehicle for either 1 week or 10 weeks. The levels of PKA, p-PKA, Akt, p-Akt, GSK3β, p-GSK3β, Dvl-3, β-catenin, and NMDA receptor subunits in the ventral midbrain were assessed by Western Blots.

RESULTS

The results showed that chronic antipsychotic treatment with aripiprazole selectively increased PKA activity in the VTA. Additionally, all three drugs elevated the activity of the Akt-GSK3β signalling pathway in a time-dependent manner, while only aripiprazole stimulated the Dvl-3-GSK3β-β-catenin signalling pathway in the SN. Furthermore, chronic administration with both aripiprazole and haloperidol decreased the expression of NMDA receptors.

CONCLUSION

This study suggests that activating PKA- and GSK3β-mediated pathways and downregulating NMDA receptor expression in the ventral midbrain might contribute to the clinical effects of antipsychotics.

Long-term Effects of Aripiprazole Treatment during Adolescence on Cognitive Function and Dopamine D2 Receptor Expression in Neurodevelopmentally Normal Rats

Objective

This study aimed to investigate the long-term effects of aripiprazole treatment during adolescence on behavior, cognitive function, and dopamine D2 receptor (D2R) expression in adult rats.

Methods

Adolescent male Sprague-Dawley rats were injected intraperitoneally with aripiprazole, risperidone, or vehicle control for 3 weeks (postnatal day 36–56). After a 2-week washout period, locomotion, anxiety, and spatial working memory were evaluated in adulthood (postnatal day 71–84), using an open field test, elevated plus maze, and Y-maze, respectively. In addition, we assessed D2R levels in the dorsolateral and medial prefrontal cortex (PFC), dorsal and ventral striatum, and hippocampus using western blot analysis.

Results

Spontaneous alternation performance (SAP) in the Y-maze, a measure of spatial working memory, differed significantly among the 3 groups (F = 3.89, p = 0.033). A post-hoc test confirmed that SAP in the aripiprazole group was significantly higher than that in the risperidone group (post-hoc test p = 0.013). D2R levels in the medial PFC (F = 8.72, p = 0.001) and hippocampus (F = 13.54, p < 0.001) were different among the 3 groups. D2R levels in the medial PFC and hippocampus were significantly lower in the aripiprazole-treated rats than that in the risperidone-treated rats (post-hoc test p = 0.025 and p < 0.001, respectively) and controls (post-hoc test p < 0.001, all).

Conclusion

This study showed that aripiprazole treatment in adolescence could influence cognitive function and dopaminergic neurotransmission into early adulthood.

Early antipsychotic treatment in juvenile rats elicits long-term alterations to the adult serotonin receptors

BACKGROUND

Antipsychotic drug (APD) prescription/use in children has increased significantly worldwide, despite limited insight into potential long-term effects of treatment on adult brain functioning. While initial long-term studies have uncovered alterations to behaviors following early APD treatment, further investigations into potential changes to receptor density levels of related neurotransmitter (NT) systems are required.

METHODS

The current investigation utilized an animal model for early APD treatment with aripiprazole, olanzapine, and risperidone in male and female juvenile rats to investigate potential long-term changes to the adult serotonin (5-HT) NT system. Levels of 5-HT1A, 5-HT2A, and 5-HT2C receptors were measured in the prefrontal cortex (PFC), caudate putamen (CPu), nucleus accumbens (NAc), and hippocampus via Western Blot and receptor autoradiography.

RESULTS

In the male cohort, long-term changes to 5-HT2A and 5-HT2C receptors were found mostly across hippocampal and cortical brain regions following early aripiprazole and olanzapine treatment, while early risperidone treatment changed 5-HT1A receptor levels in the NAc and PFC. Lesser effects were uncovered in the female cohort with aripiprazole, olanzapine and risperidone to alter 5-HT1A and 5-HT2A receptors in NAc and hippocampal brain regions, respectively.

CONCLUSION

The results of this study suggest that early treatment of various APDs in juvenile rats may cause gender and brain regional specific changes in 5-HT2A and 5-HT2C receptors in the adult brain.

Early Antipsychotic Treatment in Juvenile Rats Elicits Long-Term Alterations to the Dopamine Neurotransmitter System

Prescription of antipsychotic drugs (APDs) to children has substantially increased in recent years. Whilst current investigations into potential long-term effects have uncovered some alterations to adult behaviours, further investigations into potential changes to neurotransmitter systems are required. The current study investigated potential long-term changes to the adult dopamine (DA) system following aripiprazole, olanzapine and risperidone treatment in female and male juvenile rats. Levels of tyrosine hydroxylase (TH), phosphorylated-TH (p-TH), dopamine active transporter (DAT), and D₁ and D₂ receptors were measured via Western blot and/or receptor autoradiography. Aripiprazole decreased TH and D₁ receptor levels in the ventral tegmental area (VTA) and p-TH levels in the prefrontal cortex (PFC) of females, whilst TH levels decreased in the PFC of males. Olanzapine decreased PFC p-TH levels and increased D₂ receptor expression in the PFC and nucleus accumbens (NAc) in females only. Additionally, risperidone treatment increased D₁ receptor levels in the hippocampus of females, whilst, in males, p-TH levels increased in the PFC and hippocampus, D₁ receptor expression decreased in the NAc, and DAT levels decreased in the caudate putamen (CPu), and elevated in the VTA. These results suggest that early treatment with various APDs can cause different long-term alterations in the adult brain, across both treatment groups and genders.

Antipsychotic-induced sensitization and tolerance: Behavioral characteristics, developmental impacts, and neurobiological mechanisms

Antipsychotic sensitization and tolerance refer to the increased and decreased drug effects due to past drug use, respectively. Both effects reflect the long-term impacts of antipsychotic treatment on the brain and result from the brain's adaptive response to the foreign property of the drug. In this review, clinical evidence of the behavioral aspect of antipsychotic sensitization and tolerance is selectively reviewed, followed by an overview of preclinical literature that examines these behavioral characteristics and the related pharmacological and nonpharmacological factors. Next, recent work on the developmental impacts of adolescent antipsychotic sensitization and tolerance is presented and recent research that delineates the neurobiological mechanisms of antipsychotic sensitization and tolerance is summarized. A theoretical framework based on "drug learning and memory" principles is proposed to account for the phenomena of antipsychotic sensitization and tolerance. It is maintained that antipsychotic sensitization and tolerance follow basic principles of learning or acquisition ("induction") and memory ("expression"). The induction and expression of both effects reflect the consequences of associative and nonassociative processing and are strongly influenced by various pharmacological, environmental, and behavioral factors. Drug-induced neuroplasticity, such as functional changes of striatal dopamine D2 and prefrontal serotonin (5-HT)2A receptors and their mediated signaling pathways, in principle, is responsible for antipsychotic sensitization and tolerance. Understanding the behavioral characteristics and neurobiological underpinnings of antipsychotic sensitization and tolerance has greatly enhanced our understanding of mechanisms of antipsychotic action, and may have important implications for future drug discovery and clinical practice.

Neural changes induced by antipsychotic administration in adolescence: A review of studies in laboratory rodents

Adolescence is characterized by major remodelling processes in the brain. Use of antipsychotic drugs (APDs) in adolescents has increased dramatically in the last 20 years; however, our understanding of the neurobiological consequences of APD treatment on the adolescent brain has not kept the same pace and significant concerns have been raised. In this review, we examined currently available preclinical studies of the effects of APDs on the adolescent brain. In animal models of neuropsychiatric disorders, adolescent APD treatment appears to be protective against selected structural, behavioural and neurochemical phenotypes. In "neurodevelopmentally normal" adolescent animals, a range of short- and long-term alterations in behaviour and neurochemistry have been reported. In particular, the adolescent brain appears to be sensitive to long-term locomotor/reward effects of chronic atypical APDs in contrast with the outcomes in adults. Long-lasting changes in dopaminergic, glutamatergic and gamma-amino butyric acid-ergic systems induced by adolescent APD administration have been observed in the nucleus accumbens. A detailed examination of other potential target regions such as striatum, prefrontal cortex and ventral tegmental area is still required. Through identification of specific neural pathways targeted by adolescent APD treatment, future studies will expand the current knowledge on long-term neural outcomes which are of translational value.

Early antipsychotic exposure affects serotonin and dopamine receptor binding density differently in selected brain loci of male and female juvenile rats

BACKGROUND

Antipsychotic drugs (APDs) were developed to treat schizophrenia in adults; however they have been increasingly prescribed (mostly "off-label") for children and adolescents. This study aimed to investigate the effects of aripiprazole, olanzapine and risperidone on the binding of serotonin (5-HT) and dopamine receptors in juvenile rat brain regions that are involved in antipsychotic efficacy.

METHODS

Male and female rats were treated orally with aripiprazole (1mg/kg), olanzapine (1mg/kg), risperidone (0.3mg/kg) or vehicle 3 times/day starting from postnatal day 23 (±1day) for 20 days. Quantitative autoradiography was performed to examine the receptor binding densities.

RESULTS

Olanzapine significantly decreased 5-HT2A (5-HT2AR) and 5-HT2C receptor (5-HT2CR) binding in the prefrontal cortex (PFC), cingulate cortex (Cg) and nucleus accumbens (NAc) of both male and female rats. In the caudate putamen (CPu), olanzapine attenuated 5-HT2AR binding in both genders, and reduced 5-HT2CR binding in male rats. Olanzapine increased D2 receptor (D2R) binding in the NAcS of male rats, but decreased it in females. Olanzapine increased D1 receptor (D1R) binding in the Cg, while aripiprazole decreased D1R binding in the PFC of males. Aripiprazole significantly reduced 5-HT2AR binding in the male PFC. Risperidone decreased 5-HT2AR binding in the PFC of female rats, while attenuating D1R binding in the PFC and Cg of males. However, APDs have no effects on the binding of serotonin and dopamine transporters.

CONCLUSION

This study revealed that aripiprazole, olanzapine and risperidone affected 5-HT2AR, 5-HT2CR, 5-HTT, D1R and D2R bindings differently in the brains of juvenile male and female rats.

Early antipsychotic treatment in childhood/adolescent period has long-term effects on depressive-like, anxiety-like and locomotor behaviours in adult rats

Childhood/adolescent antipsychotic drug (APD) use is exponentially increasing worldwide, despite limited knowledge of the long-term effects of early APD treatment. Whilst investigations have found that early treatment has resulted in some alterations to dopamine and serotonin neurotransmission systems (essential to APD efficacy), there have only been limited studies into potential long-term behavioural changes. This study, using an animal model for childhood/adolescent APD treatment, investigated the long-term effects of aripiprazole, olanzapine and risperidone on adult behaviours of male and female rats. Open-field/holeboard, elevated plus maze (EPM), social interaction and forced swim (FS) tests were then conducted in adult rats. Our results indicated that in the male cohort, early risperidone and olanzapine treatment elicited long-term hyper-locomotor effects (open-field/holeboard and FS tests), whilst a decrease in depressive-like behaviour (in FS test) was observed in response to olanzapine treatment. Furthermore, anxiolytic-like behaviours were found following testing in the open-field/holeboard and EPM in response to all three drug treatments. Effects in the female cohort, however, were to a far lesser extent, with behavioural attributes indicative of an increased depressive-like behaviour and hypo-locomotor activity exhibited in the FS test following early risperidone and olanzapine treatment. These results suggest that various APDs have different long-term effects on the behaviours of adult rats.

Adolescent olanzapine sensitization is correlated with hippocampal stem cell proliferation in a maternal immune activation rat model of schizophrenia

Previous work established that repeated olanzapine (OLZ) administration in normal adolescent rats induces a sensitization effect (i.e. increased behavioral responsiveness to drug re-exposure) in the conditioned avoidance response (CAR) model. However, it is unclear whether the same phenomenon can be detected in animal models of schizophrenia. The present study explored the generalizability of OLZ sensitization from healthy animals to a preclinical neuroinflammatory model of schizophrenia in the CAR. Maternal immune activation (MIA) was induced via polyinosinic:polycytidylic acid (PolyI:C) administration into pregnant dams. Behavioral assessments of offspring first identified decreased maternal separation-induced pup ultrasonic vocalizations and increased amphetamine-induced hyperlocomotion in animals prenatally exposed to PolyI:C. In addition, repeated adolescent OLZ administration confirmed the generalizability of the sensitization phenomenon. Using the CAR test, adolescent MIA animals displayed a similar increase in behavioral responsiveness after repeated OLZ exposure during both the repeated drug test days as well as a subsequent challenge test. Neurobiologically, few studies examining the relationship between hippocampal cell proliferation and survival and either antipsychotic exposure or MIA have incorporated concurrent behavioral changes. Thus, the current study also sought to reveal the correlation between OLZ behavioral sensitization in the CAR and hippocampal cell proliferation and survival. 5'-bromodeoxyuridine immunohistochemistry identified a positive correlation between the magnitude of OLZ sensitization (i.e. change in avoidance suppression induced by OLZ across days) and hippocampal cell proliferation. The implications of the relationship between behavioral and neurobiological results are discussed.

Effects of central activation of serotonin 5-HT2A/2C or dopamine D 2/3 receptors on the acute and repeated effects of clozapine in the conditioned avoidance response test

RATIONALE

Acute administration of clozapine (a gold standard of atypical antipsychotics) disrupts avoidance response in rodents, while repeated administration often causes a tolerance effect.

OBJECTIVE

The present study investigated the neuroanatomical basis and receptor mechanisms of acute and repeated effects of clozapine treatment in the conditioned avoidance response test in male Sprague-Dawley rats.

METHODS

2,5-dimethoxy-4-iodo-amphetamine (DOI, a preferential 5-HT2A/2C agonist) or quinpirole (a preferential dopamine D2/3 agonist) was microinjected into the medial prefrontal cortex (mPFC) or nucleus accumbens shell (NAs), and their effects on the acute and long-term avoidance disruptive effect of clozapine were tested.

RESULTS

Intra-mPFC microinjection of quinpirole enhanced the acute avoidance disruptive effect of clozapine (10 mg/kg, sc), while DOI microinjections reduced it marginally. Repeated administration of clozapine (10 mg/kg, sc) daily for 5 days caused a progressive decrease in its inhibition of avoidance responding, indicating tolerance development. Intra-mPFC microinjection of DOI at 25.0 (but not 5.0) μg/side during this period completely abolished the expression of clozapine tolerance. This was indicated by the finding that clozapine-treated rats centrally infused with 25.0 μg/side DOI did not show higher levels of avoidance responses than the vehicle-treated rats in the clozapine challenge test. Microinjection of DOI into the mPFC immediately before the challenge test also decreased the expression of clozapine tolerance.

CONCLUSIONS

Acute behavioral effect of clozapine can be enhanced by activation of the D2/3 receptors in the mPFC. Clozapine tolerance expression relies on the neuroplasticity initiated by its antagonist action against 5-HT2A/2C receptors in the mPFC.

Asenapine sensitization from adolescence to adulthood and its potential molecular basis

Asenapine is a new antipsychotic drug that induces a long-lasting behavioral sensitization in adult rats. The present study investigated the developmental impacts of adolescent asenapine treatment on drug sensitivity and on 3 proteins implicated in the action of antipsychotic drugs (i.e. brain-derived neurotrophic factor (BDNF), dopamine D2 receptor, and ΔFosB) in adulthood. Male adolescent Sprague-Dawley rats (postnatal days, P 43-48) were first treated with asenapine (0.05, 0.10 or 0.20mg/kg, sc) and tested in the conditioned avoidance or PCP (2.0mg/kg, sc)-induced hyperlocomotion tasks for 5 days. After they became adults (∼P 76), asenapine sensitization was assessed in a single avoidance or PCP-induced hyperlocomotion challenge test with all rats being injected with asenapine (0.10mg/kg, sc). Rats were then sacrificed 1 day later and BDNF, D2 and ΔFosB in the prefrontal cortex, striatum and hippocampus were examined using Western blotting. In adolescence, repeated asenapine treatment produced a persistent and dose-dependent inhibition of avoidance response, spontaneous motor activity and PCP-induced hyperlocomotion. In the asenapine challenge test, adult rats treated with asenapine (0.10 and 0.20mg/kg) in adolescence made significantly fewer avoidance responses and showed a stronger inhibition of spontaneous motor activity than those previously treated with saline. However, no group difference in the levels of BDNF, D2 and ΔFosB expression was found. These findings suggest that although adolescent asenapine treatment for a short period of time induces a robust behavioral sensitization that persists into adulthood, such a long-term effect is not likely to be mediated by BDNF, D2 and ΔFosB.

Long-lasting sensitization induced by repeated risperidone treatment in adolescent Sprague-Dawley rats: a possible D2 receptor mediated phenomenon?

RATIONALE

Risperidone use in children and adolescents for the treatment of various neuropsychiatric disorders (e.g., schizophrenia, autism, disruptive behavior, etc.) has increased substantially in recent decades. However, its long-term effect on the brain and behavioral functions is not well understood.

OBJECTIVE

The present study investigated how a short-term risperidone treatment in adolescence impacts antipsychotic response in adulthood in the conditioned avoidance response and phencyclidine (PCP)-induced hyperlocomotion tests.

METHODS

Male adolescent Sprague-Dawley rats (postnatal days [P] 40-44 or 43-48) were first treated with risperidone (0.3, 0.5, or 1.0 mg/kg, subcutaneously (sc)) and tested in the conditioned avoidance or PCP (3.2 mg/kg, sc)-induced hyperlocomotion model daily for five consecutive days. After they became adults (~P 76-80), they were challenged with risperidone (0.3 mg/kg, sc) to assess their sensitivity to risperidone reexposure. A quinpirole (a D2/3 receptor agonist, 1.0 mg/kg, sc)-induced hyperlocomotion test was later conducted to assess the risperidone-induced functional changes in D2 receptor.

RESULTS

In the risperidone challenge test in adulthood, adult rats previously treated with risperidone in adolescence made significantly fewer avoidance responses and exhibited significantly lower PCP-induced hyperlocomotion than those previously treated with vehicle. They also appeared to be more hyperactive than the vehicle-pretreated ones in the quinpirole-induced hyperlocomotion test. Prepulse inhibition of acoustic startle or fear-induced 22 kHz ultrasonic vocalizations in adulthood was not altered by adolescence risperidone treatment.

CONCLUSIONS

Adolescent risperidone exposure induces a long-term increase in behavioral sensitivity to risperidone that persists into adulthood. This long-lasting change might be due to functional upregulation of D2-mediated neurotransmission.

Adult response to olanzapine or clozapine treatment is altered by adolescent antipsychotic exposure: a preclinical test in the phencyclidine hyperlocomotion model

This study examined how repeated olanzapine (OLZ) or clozapine (CLZ) treatment in adolescence alters sensitivity to the same drug in adulthood in the phencyclidine (PCP) hyperlocomotion model. Male adolescent Sprague-Dawley rats (postnatal day (P) 44-48) were first treated with OLZ (1.0 or 2.0 mg/kg, subcutaneously (sc)) or CLZ (10.0 or 20.0 mg/kg, sc) and tested in the PCP (3.2 mg/kg, sc)-induced hyperlocomotion model for five consecutive days. Then a challenge test with OLZ (0.5 mg/kg) or CLZ (5.0 mg/kg) was administered either during adolescence (~P 51) or after the rats matured into adults (~P 76 and 91). During adolescence, repeated OLZ or CLZ treatment produced a persistent inhibition of PCP-induced hyperlocomotion across the five test days. In the challenge test during adolescence, rats previously treated with OLZ did not show a significantly stronger inhibition of PCP-induced hyperlocomotion than those previously treated with vehicle (VEH). In contrast, those previously treated with CLZ showed a weaker inhibition than the VEH controls. When assessed in adulthood, the enhanced sensitivity to OLZ and the decreased sensitivity to CLZ were detected on ~P 76, even on ~P 91 in the case of OLZ. These findings suggest that adolescent OLZ or CLZ exposure can induce long-term alterations in antipsychotic response that persist into adulthood.

Long-term impacts of adolescent risperidone treatment on behavioral responsiveness to olanzapine and clozapine in adulthood

This preclinical study investigated how a short-term risperidone treatment in adolescence impacts antipsychotic response to olanzapine and clozapine in adulthood. Antipsychotic effect was indexed by a drug's suppressive effect on avoidance responding in a rat conditioned avoidance response (CAR) model. Male adolescent Sprague-Dawley rats were first treated with risperidone (1.0mg/kg, sc) or sterile water and tested in the CAR model for 5 consecutive days from postnatal days P 40 to 44. After they became adults (~P 80-84), they were switched to olanzapine (0.5mg/kg, sc), clozapine (5.0mg/kg, sc) or vehicle treatment and tested for avoidance for 5days. During the adolescent period, repeated risperidone treatment produced a persistent inhibition of avoidance response. Throughout the 5days of adulthood drug testing, rats previously treated with risperidone in adolescence made significantly fewer avoidance responses than the vehicle ones when they all were switched to olanzapine, indicating a risperidone-induced enhancement of behavioral sensitivity to olanzapine. In contrast, when switched to clozapine, rats previously treated with risperidone made significantly more avoidance responses than the vehicle rats, indicating a risperidone-induced decrease of behavioral sensitivity to clozapine. Performance in the prepulse inhibition of acoustic startle response in adulthood was not altered by adolescent risperidone treatment. Collectively, adolescent risperidone exposure induced a long-term change in behavioral sensitivity to other atypical antipsychotic drugs, with the specific direction of change (i.e., increase or decrease) dependent on the drug to be switched to. These long-lasting changes are likely mediated by drug-induced neuroplastic changes and may also have significant clinical implications for antipsychotic treatment of chronic patients with an early onset of psychotic symptoms.

Clozapine pre-treatment has a protracted hypolocomotor effect on the induction and expression of amphetamine sensitization

Amphetamine locomotor sensitization is an animal model for the study of addiction and schizophrenia. The antipsychotic clozapine blocks the hyperlocomotion induced by an acute injection of amphetamine, but its effect on locomotor sensitization after repeated amphetamine administration remains unknown. In the present study we investigate the effect of repeated administration of clozapine on the induction and expression of amphetamine locomotor sensitization. We propose that repeated administration of clozapine blocks the induction and expression of amphetamine sensitization. Male Sprague-Dawley rats were classified according to their locomotor response to an acute saline injection in high responder saline (HRS) or low responder saline (LRS). Rats from both groups were injected once daily with amphetamine for 5 consecutive days. Horizontal locomotor activity was measured during 40 min. Four days after the last injection, an acute dose of amphetamine was administered to assess the expression of sensitization. Clozapine was injected once daily for 4 consecutive days before (pre-treatment) or after (treatment) induction of sensitization. Pre-treatment with clozapine significantly decreases both acute amphetamine-induced hyperlocomotion and the induction and expression of amphetamine sensitization only in LRS rats, showing a protracted hypolocomotor effect. On the other hand, clozapine treatment had no effect over locomotor response on the expression of amphetamine sensitization in either LRS or HRS rats. These data suggest that clozapine effect on amphetamine locomotor response depends on individual differences. Also, our results suggest that clozapine pre-treatment attenuates the neuroplasticity underlying amphetamine sensitization, but clozapine treatment is unable to reverse these changes once amphetamine sensitization has been induced.

Repeated asenapine treatment produces a sensitization effect in two preclinical tests of antipsychotic activity

Among several commonly used atypical antipsychotic drugs, olanzapine and risperidone cause a sensitization effect in the conditioned avoidance response (CAR) and phencyclidine (PCP)-induced hyperlocomotion paradigms--two well established animal tests of antipsychotic drugs, whereas clozapine causes a tolerance effect. Asenapine is a novel antipsychotic drug recently approved for the treatment of schizophrenia and manic disorders. It shares several receptor binding sites and behavioral features with other atypical antipsychotic drugs. However, it is not clear what type of repeated effect (sensitization or tolerance) asenapine would induce, and whether such an effect is transferrable to other atypicals. In this study, male adult Sprague-Dawley rats were first repeatedly tested with asenapine (0.05, 0.10 or 0.20 mg/kg, sc) for avoidance response or PCP (3.20 mg/kg, sc)-induced hyperlocomotion daily for 5 consecutive days. After 2-3 days of retraining/drug-free recovery, they were then challenged with asenapine (0.10 mg/kg, sc), followed by olanzapine (0.50 mg/kg, sc) and clozapine (2.50 mg/kg, sc). During the 5-day drug test period (the induction phase), repeated asenapine treatment progressively increased its inhibition of avoidance response and PCP-induced hyperlocomotion in a dose-dependent fashion. On the asenapine and olanzapine challenge tests (the expression phase), rats previously treated with asenapine still showed significantly lower avoidance response and lower PCP-induced hyperlocomotion than those previously treated with vehicle. An increased reactivity to clozapine challenge in prior asenapine-treated rats was also found in the PCP-induced hyperlocomotion test. These findings suggest that asenapine is capable of inducing a sensitization effect and a cross-sensitization to olanzapine and clozapine (to a lesser extent). Because the behavioral profile of asenapine in both tests is similar to that of olanzapine, but different from that of clozapine, we suggest that asenapine resembles olanzapine to a greater extent than clozapine in its therapeutic and side effect profiles.

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.

Olanzapine sensitization and clozapine tolerance: from adolescence to adulthood in the conditioned avoidance response model

Disruption of conditioned avoidance response (CAR) in rodents is one trademark feature of many antipsychotic drugs. In adult rats, repeated olanzapine (OLZ) treatment causes an enhanced disruption of avoidance response (sensitization), whereas repeated clozapine (CLZ) treatment causes a decreased disruption (tolerance). The present study addressed (1) whether OLZ sensitization and CLZ tolerance can be induced in adolescent rats, and (2) the extent to which OLZ sensitization and CLZ tolerance induced in adolescence persists into adulthood. Male adolescent Sprague-Dawley rats (approximate postnatal days (∼P) 43-47) were first treated with OLZ (1.0 or 2.0 mg/kg, subcutaneously (sc)) or CLZ (10 or 20 mg/kg, sc) daily for 5 consecutive days in the CAR model. They were then tested for the expression of OLZ sensitization or CLZ tolerance either in adolescence (∼P 50) or after they matured into adults (∼P 76 and 92) in a challenge test during which all rats were injected with either a lower dose of OLZ (0.5 mg/kg) or CLZ (5.0 mg/kg). When tested in adolescence, rats previously treated with OLZ showed a stronger inhibition of CAR than those previously treated with vehicle (ie, sensitization). In contrast, rats previously treated with CLZ showed a weaker inhibition of CAR than those previously treated with vehicle (ie, tolerance). When tested in adulthood, the OLZ sensitization was still detectable at both time points (∼P 76 and 92), whereas the CLZ tolerance was only detectable on ∼P 76, and only manifested in the intertrial crossing. Performance in the prepulse inhibition and fear-induced 22 kHz ultrasonic vocalizations in adulthood were not altered by adolescence drug treatment. Collectively, these findings suggest that atypical antipsychotic treatment during adolescence can induce a long-term specific alteration in antipsychotic effect that persists into adulthood despite the brain maturation. As antipsychotic drugs are being increasingly used in children and adolescents in the past two decades, findings from this study are important for understanding the impacts of adolescent antipsychotic treatment on the brain and behavioral developments. This work also has implications for clinical practice involving adolescence antipsychotic treatments in terms of drug choice, drug dose, and schedule.

Risperidone administered during asymptomatic period of adolescence prevents the emergence of brain structural pathology and behavioral abnormalities in an animal model of schizophrenia

Schizophrenia is a disorder of a neurodevelopmental origin manifested symptomatically after puberty. Structural neuroimaging studies show that neuroanatomical aberrations precede onset of symptoms, raising a question of whether schizophrenia can be prevented. Early treatment with atypical antipsychotics may reduce the risk of transition to psychosis, but it remains unknown whether neuroanatomical abnormalities can be prevented. We have recently shown, using in vivo structural magnetic resonance imaging, that treatment with the atypical antipsychotic clozapine during an asymptomatic period of adolescence prevents the emergence of schizophrenia-like brain structural abnormalities in adult rats exposed to prenatal immune challenge, in parallel to preventing behavioral abnormalities. Here we assessed the preventive efficacy of the atypical antipsychotic risperidone (RIS). Pregnant rats were injected on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (poly I:C) or saline. Their male offspring received daily RIS (0.045 or 1.2 mg/kg) or vehicle injection in peri-adolescence (postnatal days [PND] 34-47). Structural brain changes and behavior were assessed at adulthood (from PND 90). Adult offspring of poly I:C-treated dams exhibited hallmark structural abnormalities associated with schizophrenia, enlarged lateral ventricles and smaller hippocampus. Both of these abnormalities were absent in the offspring of poly I:C dams that received RIS at peri-adolescence. This was paralleled by prevention of schizophrenia-like behavioral abnormalities, attentional deficit, and hypersensitivity to amphetamine in these offspring. We conclude that pharmacological intervention during peri-adolescence can prevent the emergence of behavioral abnormalities and brain structural pathology resulting from in utero insult. Furthermore, highly selective 5HT(2A) receptor antagonists may be promising targets for psychosis prevention.

Clozapine, but not olanzapine, disrupts conditioned avoidance response in rats by antagonizing 5-HT2A/2C receptors

The present study was designed to assess the role of 5-HT(2A/2C) receptors in the acute and repeated effect of clozapine and olanzapine in a rat conditioned avoidance response model, a validated model of antipsychotic activity. Male Sprague-Dawley rats that were previously treated with either phencyclidine (0.5-2.0 mg/kg, sc), amphetamine (1.25-5.0 mg/kg, sc), or saline and tested in a prepulse inhibition of acoustic startle study were used. They were first trained to acquire avoidance response to a white noise (CS1) and a pure tone (CS2) that differed in their ability to predict the occurrence of footshock. Those who acquired avoidance response were administered with clozapine (10.0 mg/kg, sc) or olanzapine (1.0 mg/kg, sc) together with either saline or 1-2,5-dimethoxy-4-iodo-amphetamine (DOI, a selective 5-HT(2A/2C) agonist, 1.0 or 2.5 mg/kg, sc), and their conditioned avoidance responses were tested for four consecutive days. After two drug-free retraining days, the long-term repeated effect was assessed in a challenge test during which all rats were injected with a low dose of clozapine (5 mg/kg, sc) or olanzapine (0.5 mg/kg). Results show that pretreatment of DOI dose-dependently reversed the acute disruptive effect of clozapine on both CS1 and CS2 avoidance responses, whereas it had little effect in reversing the acute effect of olanzapine. On the challenge test, pretreatment of DOI did not alter the clozapine-induced tolerance or the olanzapine-induced sensitization effect. These results confirmed our previous findings and suggest that clozapine, but not olanzapine, acts on through 5-HT(2A/2C) receptors to achieve its acute avoidance disruptive effect and likely its therapeutic effects. The long-term clozapine tolerance and olanzapine sensitization effects appear to be mediated by non-5-HT(2A/2C) receptors.

Developmental trajectories during adolescence in males and females: a cross-species understanding of underlying brain changes

Adolescence is a transitional period between childhood and adulthood that encompasses vast changes within brain systems that parallel some, but not all, behavioral changes. Elevations in emotional reactivity and reward processing follow an inverted U shape in terms of onset and remission, with the peak occurring during adolescence. However, cognitive processing follows a more linear course of development. This review will focus on changes within key structures and will highlight the relationships between brain changes and behavior, with evidence spanning from functional magnetic resonance imaging (fMRI) in humans to molecular studies of receptor and signaling factors in animals. Adolescent changes in neuronal substrates will be used to understand how typical and atypical behaviors arise during adolescence. We draw upon clinical and preclinical studies to provide a neural framework for defining adolescence and its role in the transition to adulthood.

Tracing the development of psychosis and its prevention: what can be learned from animal models

Schizophrenia (SCZ) is a neurodevelopmental disorder manifested symptomatically after puberty whose pharmacotherapy remains unsatisfactory. In recent years, longitudinal structural neuroimaging studies have revealed that neuroanatomical aberrations occur in this disorder and in fact precede symptom onset, raising the exciting possibility that SCZ can be prevented. There is some evidence that treatment with atypical antipsychotic drugs (APDs) prior to the development of the full clinical phenotype reduces the risk of transition to psychosis, but results remain controversial. It remains unknown whether progressive structural brain aberrations can be halted. Given the diagnostic, ethical, clinical and methodological problems of pharmacological and imaging studies in patients, getting such information remains a major challenge. Animal neurodevelopmental models of SCZ are invaluable for investigating such questions because they capture the notion that the effects of early brain damage are progressive. In recent years, data derived from such models have converged on key neuropathological and behavioral deficits documented in SCZ attesting to their strong validity, and making them ideal tools for evaluating progression of pathology following in-utero insults as well as its prevention. We review here our recent studies that use longitudinal in vivo structural imaging to achieve this aim in the prenatal immune stimulation model that is based on the association of prenatal infection and increased risk for SCZ. Pregnant rats were injected on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (poly I:C) or saline. Male and female offspring were imaged and tested behaviorally on postnatal days (PNDs) 35, 46, 56, 70 and 90. In other experiments, offspring of poly I:C- and saline-treated dams received the atypical antipsychotic drugs (APDs) clozapine or risperidone in two developmental windows: PND 34-47 and PND 48-61, and underwent behavioral testing and imaging at adulthood. Prenatal poly I:C-induced interference with fetal brain development led to aberrant postnatal brain development as manifested in structural abnormalities in the hippocampus, the striatum, the prefrontal cortex and lateral ventricles (LV), as seen in SCZ. The specific trajectories were region-, age- and sex-specific, with females having delayed onset of pathology compared to males. Brain pathology was accompanied by development of behavioral abnormalities phenotypic of SCZ, attentional deficit and hypersensitivity to amphetamine, with same sex difference. Hippocampal volume loss and LV volume expansion as well as behavioral abnormalities were prevented in the offspring of poly I:C mothers who received clozapine or risperidone during the asymptomatic period of adolescence (PND 34-47). Administration at a later window, PNDs 48-61, exerted sex-, region- and drug- specific effects. Our data show that prenatal insult leads to progressive postnatal brain pathology, which gradually gives rise to "symptoms"; that treatment with atypical APDs can prevent both brain and behavioral pathology; and that the earlier the intervention, the more pathological outcomes can be prevented.

Annual Research Review: New frontiers in developmental neuropharmacology: can long-term therapeutic effects of drugs be optimized through carefully timed early intervention?

Our aim is to present a working model that may serve as a valuable heuristic to predict enduring effects of drugs when administered during development. Our primary tenet is that a greater understanding of neurodevelopment can lead to improved treatment that intervenes early in the progression of a given disorder and prevents symptoms from manifesting. The immature brain undergoes significant changes during the transitions between childhood, adolescence, and adulthood. Such changes in innervation, neurotransmitter levels, and their respective signaling mechanisms have profound and observable changes on typical behavior, but also increase vulnerability to psychiatric disorders when the maturational process goes awry. Given the remarkable plasticity of the immature brain to adapt to its external milieu, preventive interventions may be possible. We intend for this review to initiate a discussion of how currently used psychotropic agents can influence brain development. Drug exposure during sensitive periods may have beneficial long-term effects, but harmful delayed consequences may be possible as well. Regardless of the outcome, this information needs to be used to improve or develop alternative approaches for the treatment of childhood disorders. With this framework in mind, we present what is known about the effects of stimulants, antidepressants, and antipsychotics on brain maturation (including animal studies that use more clinically-relevant dosing paradigms or relevant animal models). We endeavor to provocatively set the stage for altering treatment approaches for improving mental health in non-adult populations.

Alterations in dopamine and glutamate neurotransmission in tetrahydrobiopterin deficient spr-/- mice: relevance to schizophrenia

Tetrahydrobiopterin (BH4) is a pivotal cofactor for enzymes responsible for the synthesis and release of monoamine neurotransmitters including dopamine (DA) and serotonin (5-HT) as well as the release of glutamate (Glu). Deficiencies in BH4 levels and reduced activities of BH(4)-associated enzymes have been recently reported in patients with schizophrenia. Accordingly, it is possible that abnormalities in the biochemical cascades regulated by BH(4) may alter DA, 5-HT and Glu neurotransmission, and consequently contribute to the pathophysiology of different neuropsychiatric diseases including schizophrenia. The development of a novel strain of mutant mice that is deficient in BH(4) by knocking out the expression of a functional sepiapterin reductase gene (spr -/-) has added new insights into the potential role of BH(4) in the pathophysiology and improved treatment of schizophrenia.

Distinct neural mechanisms underlying acute and repeated administration of antipsychotic drugs in rat avoidance conditioning

RATIONALE

Acute antipsychotic treatment disrupts conditioned avoidance responding, and repeated treatment induces a sensitization- or tolerance-like effect. However, the neurochemical mechanisms underlying both acute and repeated antipsychotic effects remain to be determined.

OBJECTIVE

The present study examined the neuroreceptor mechanisms of haloperidol, clozapine, and olanzapine effect in a rat two-way conditioned avoidance model.

METHODS

Well-trained Sprague-Dawley rats were administered with haloperidol (0.05 mg/kg, sc), clozapine (10.0 mg/kg, sc), or olanzapine (1.0 mg/kg, sc) together with either saline, quinpirole (a selective dopamine D(2/3) agonist, 1.0 mg/kg, sc), or 2,5-dimethoxy-4-iodo-amphetamine (DOI; a selective 5-HT(2A/2C) agonist, 2.5 mg/kg, sc), and their conditioned avoidance responses were tested over 3 days. After 2 days of drug-free retraining, the repeated treatment effect was assessed in a challenge test.

RESULTS

Pretreatment of quinpirole, but not DOI, attenuated the acute haloperidol-induced disruption of avoidance responding and to a lesser extent, olanzapine-induced disruption. In contrast, pretreatment of DOI, but not quinpirole, attenuated the acute effect of clozapine. On the repeated effect, pretreatment of DOI, but not quinpirole, attenuated the potentiated disruption of haloperidol, whereas pretreatment of quinpirole attenuated the potentiated disruption of olanzapine but enhanced the tolerance-like effect of clozapine.

CONCLUSIONS

These findings suggest that acute haloperidol and olanzapine disrupt avoidance responding primarily by blocking dopamine D(2) receptors, whereas acute clozapine exerts its disruptive effect primarily by blocking the 5-HT(2A) receptors. The repeated haloperidol effect may be mediated by 5-HT(2A/2C) blockade-initiated neural processes, whereas the repeated clozapine and olanzapine effect may be mediated by D(2/3) blockade-initiated neural processes.

Clozapine administration in adolescence prevents postpubertal emergence of brain structural pathology in an animal model of schizophrenia

BACKGROUND

Schizophrenia is a neuropsychiatric disorder of a neurodevelopmental origin manifested symptomatically after puberty. Structural neuroimaging studies show that neuroanatomical aberrations occur before onset of symptoms, raising a question of whether schizophrenia can be prevented. Treatment with atypical antipsychotic drugs before the development of the full clinical phenotype might reduce the risk of transition to psychosis, but it remains unknown whether neuroanatomical abnormalities can be prevented. We used a neurodevelopmental animal model of schizophrenia to assess the efficacy of the atypical antipsychotic clozapine to prevent neuroanatomical deterioration.

METHODS

Pregnant rats received injection on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (PolyI:C) or saline. Structural brain changes in the male offspring were assessed at adolescence and adulthood (35 days and 120 days) with structural neuroimaging. In the second part, male offspring of PolyI:C- and saline-treated dams received daily clozapine (7.5 mg/kg) or saline injection in adolescence (days 34-47) and underwent behavioral testing and imaging at adulthood (from 90 days onward).

RESULTS

In utero exposure to maternal infection led in the offspring to postpubertal emergence of hallmark structural abnormalities associated with schizophrenia, enlarged ventricles, and smaller hippocampus. These abnormalities were not observed in the offspring of mothers who received PolyI:C that were treated with clozapine in adolescence. This was paralleled by prevention of behavioral abnormalities phenotypic of schizophrenia, attentional deficit, and hypersensitivity to amphetamine.

CONCLUSIONS

This is the first demonstration that pharmacological intervention during adolescence can prevent the emergence of brain structural changes resulting from in-utero insult.

Antipsychotics in children and adolescents: increasing use, evidence for efficacy and safety concerns

Second-generation antipsychotics (SGA) are increasingly used to treat children and adolescents. The European College of Neuro-psychopharmacology convened an expert panel to review relevant efficacy and safety data, and identify needs for further research. Controlled studies support the short-term efficacy of several SGA for treating psychosis, mania, and aggression within certain diagnostic categories. Except for clozapine, no clinically significant superiority in efficacy has been demonstrated for any specific antipsychotic, including both first- and second-generation agents, in children and adolescents. Major differences exist, however, with respect to type and severity of adverse effects; therefore the choice of treatment is primarily guided by tolerability and safety considerations. Children appear to be at higher risk than adults for a number of adverse effects, such as extrapyramidal symptoms and metabolic and endocrine abnormalities. While the safety profile during acute and intermediate treatment has been evaluated, the distal benefit/risk ratio during long-term treatment remains to be determined. Research is also needed to understand the mechanisms underlying antipsychotic-induced toxicities in order to develop effective preventive and treatment strategies.

Drugs, biogenic amine targets and the developing brain

Defects in the development of the brain have a profound impact on mature brain functions and underlying psychopathology. Classical neurotransmitters and neuromodulators, such as dopamine, serotonin, norepinephrine, acetylcholine, glutamate and GABA, have pleiotropic effects during brain development. In other words, these molecules produce multiple diverse effects to serve as regulators of distinct cellular functions at different times in neurodevelopment. These systems are impacted upon by abuse of a variety of illicit drugs, neurotherapeutics and environmental contaminants. In this review, we describe the impact of drugs and chemicals on brain formation and function in animal models and in human populations, highlighting sensitive periods and effects that may not emerge until later in life.

Differential regional and dose-related effects of asenapine on dopamine receptor subtypes

RATIONALE

The novel psychopharmacologic agent, asenapine, has high affinity for a range of receptors including the dopaminergic receptors.

OBJECTIVE

We examined the long-term effects of multiple doses of asenapine on dopamine receptor subtypes: D(1)-like (D(1) and D(5)), D(2), D(3), and D(4).

METHODS

Rats were given asenapine 0.03, 0.1, or 0.3 mg/kg (subcutaneously, twice daily) or vehicle for 4 weeks. Receptor binding was determined by autoradiography from brain sections collected from the medial prefrontal cortex (mPFC), dorsolateral frontal cortex, caudate putamen (CPu), nucleus accumbens (NAc), and hippocampus (HIP).

RESULTS

Four weeks of asenapine at 0.3 mg/kg significantly (P < 0.05) increased D(1)-like binding in the mPFC (by 26%), NAc (59%), and CPu (55%). Asenapine (0.1 and 0.3 mg/kg) also increased D(2) binding in mPFC (43% and 55%, respectively). All doses of asenapine dose-dependently increased D(2) binding in HIP (by 32%, 45%, and 63%, respectively). In contrast, only 0.3 mg/kg of asenapine significantly (P < 0.05) increased D(2) binding in the NAc (32%) and CPu (41%). Repeated treatment with 0.1 and 0.3 mg/kg of asenapine increased D(4) binding in the NAc (36% and 71%), CPu (27% and 70%), and HIP (48% and 77%). However, asenapine, at the doses tested, did not significantly alter D(3) binding in the brain regions examined in this study.

CONCLUSIONS

These results indicate that asenapine has region-specific and dose-dependent effects on dopamine receptor subtypes in rat forebrain, which may contribute to asenapine's unique psychopharmacological properties.

Effects of risperidone on dopamine receptor subtypes in developing rat brain

The atypical antipsychotic risperidone is often prescribed to pediatric patients with neuropsychiatric disorders, though its effects on the developing brain remain unclear. Accordingly, we studied the effects of repeated treatment of risperidone on dopamine receptors in brain regions of juvenile rat. Levels of dopamine receptors (D(1), D(2), D(3), D(4)) in forebrain regions of juvenile rats were quantified after 3 weeks of treatment with three different doses of risperidone (0.3, 1.0 and 3.0 mg/kg) and compared findings to those in adult rats treated with risperidone (3.0 mg/kg/day) previously. Risperidone (at 1.0 and 3.0 mg/kg/day) increased levels of D(1) receptors in nucleus accumbens and caudate-putamen of juvenile, but not adult rats. Conversely, all three doses of risperidone dose-dependently increased D(2) labeling in medial prefrontal cortex and hippocampus, and D(4) receptor in nucleus accumbens, caudate-putamen and hippocampus of juvenile animals as well as in adults. Only the high dose of risperidone (3.0 mg/kg) increased D(2) receptors in caudate-putamen in both juvenile and adult brain. D(3) receptors were not altered by risperidone in any brain region at any dose or age. The findings indicate dose-dependent effects of risperidone on dopamine receptors in developing animals, and that juvenile animals are more sensitive than adults to the cerebral effects of risperidone.

Differently lasting effects of prenatal and postnatal chronic clozapine/haloperidol on activity and memory in mouse offspring

We evaluated the behavioral effects of chronic haloperidol (HAL) and clozapine (CLO) during gestation and CNS development, compared with transient treatments that stopped 1-3 weeks before the test.

RESULTS

1) Chronic HAL (6 mg/l in drinking water) but not HAL-withdrawal caused hypo-activity in open-field test on postnatal days (PNDs) 35, 42 and 56. However, hyper-activity was found in both CLO (90 mg/l) and CLO-withdrawal pups. 2) In the step-through test, retention performance was significantly higher in HAL-treated mice than in the controls on PND 42, as well as in withdrawal mice on PNDs 35 and 42. However, both chronic CLO (90 mg/l) exposure and CLO-withdrawal tended to improve the acquisition of memory. Furthermore, chronic CLO (180 mg/l) ameliorated scopolamine (3 mg/kg)-induced impairment of memory on PND 56. 3) In the water-maze test, both chronic HAL and HAL-withdrawal treatments significantly impaired performance on the 4th training day at PND 35, but not PNDs 42 and 56. Neither chronic CLO exposure nor CLO-withdrawal affected spatial memory. 4) Body weight following HAL/CLO administration decreased when compared with the controls during PND 21-35, but approached control levels at PND 40.

CONCLUSION

HAL doesn't elicit permanent behavioral changes in offspring. By contrast, CLO had longer-lasting effects than HAL. The pups at age before PND 35 seem more sensitive to HAL/CLO than elder pups.