Effects of chronic treatments with SM-9018, a potential atypical neuroleptic, on behavioral dopaminergic and serotonergic sensitivities in rats

Perospirone

Perospirone is an atypical antipsychotic agent for the treatment of schizophrenia. Its primary mode of action is through antagonism of serotonin 5-HT2A and dopamine D2 receptors. An 8-week course of oral perospirone 8 to 48 mg/day displayed efficacy in up to 75% of patients with schizophrenia participating in phase II and phase III trials. The onset of action of the drug was about 2 weeks. Perospirone was effective against positive, negative and general symptoms in patients with schizophrenia, as assessed with standard rating scales (Brief Psychiatric Rating Scale, Positive and Negative Symptom Scale). Compared with haloperidol 2 to 12 mg/day, perospirone 8 to 48 mg/day was significantly more effective against negative symptoms and tended to be more effective against general symptoms and most positive symptoms in a trial in 145 patients with schizophrenia. Perospirone had efficacy similar to that of mosapramine 50 to 300 mg/day in a comparative phase III trial in 159 patients. Extrapyramidal symptoms (EPS) tended to occur less often and were generally milder with perospirone than with haloperidol or mosapramine.

Chronic haloperidol administration does not block acute nicotine-induced improvements in radial-arm maze performance in the rat

Nicotine has been found to improve cognitive performance in a variety of tasks including the radial maze. Nicotine has also been shown to promote the release of a variety of neurotransmitters including dopamine (DA). DA has been found to be important for nicotine's reinforcing effects. DA involvement with nicotine's cognitive effects is unclear. In the current study, the effects of acute nicotine injections (0, 0.1, 0.2, or 0.4 mg/kg) were examined on radial-arm maze performance in rats given chronic infusions the DA antagonist haloperidol (0, 0.2, or 0.6 mg/kg/day). Chronic haloperidol infusion was not found to attenuate the memory improvement caused by acute nicotine injection. In fact, the dose-related nicotine-induced memory improvement was clearer in the haloperidol-treated groups than in controls. This is similar to the effect of nicotine we saw in human subjects given chronic doses of haloperidol. Our previous studies demonstrated significant nicotinic-DA interactions with regard to memory function. The current results suggest that in the DA-nicotinic relationship DA stimulation is not necessary for the memory improvement caused by nicotine.

Effects of perospirone (SM-9018), a potential atypical neuroleptic, on dopamine D1 receptor-mediated vacuous chewing movement in rats: a role of 5-HT2 receptor blocking activity

We compared the acute and subacute effects of perospirone (SM-9018), a novel neuroleptic with potent 5-HT2 and D2 blocking actions, and of haloperidol (HAL) on dopamine D1 receptor-mediated vacuous chewing movement (VCM) in rats. A selective D1 agonist, SKF 38393 (SKF), markedly increased the incidence of VCM, which was blocked by SCH 23390 (a D1 antagonist) but not by sulpiride (a D2 antagonist). Perospirone and HAL inhibited the SKF-induced VCM in a dose-dependent manner. The potency of the inhibitory actions of perospirone was considerably weaker (about 30 times) than that of HAL despite their similar affinities for D1 receptors. Subacute treatment with perospirone for 2 weeks failed to affect the behavioral sensitivity of rats to SKF. However, the HAL treatment markedly enhanced the incidence of the SKF-induced VCM. On the other hand, the selective 5-HT2 antagonists ritanserin and ketanserin significantly reduced the inhibitory actions of HAL and SCH 23390 on the SKF-induced VCM. In addition, combined treatment of ritanserin with HAL for 2 weeks abolished the enhancement of SKF-induced VCM by HAL treatment. These findings suggest that perospirone is weaker than HAL in altering the behavioral sensitivity of D1 receptor-mediated VCM under repeated administration, which may be related to the 5-HT2 blocking activity of perospirone.

Evaluation of perospirone (SM-9018), a novel serotonin-2 and dopamine-2 receptor antagonist, and other antipsychotics in the conditioned fear stress-induced freezing behavior model in rats

We studied the effects of perospirone (SM-9018), a novel serotonin-2 (5-HT2) and dopamine-2 (D2) receptor antagonist (SDA), on conditioned fear stress (CFS)-induced freezing behavior in rats and compared its actions with those of other antipsychotics. Exposure of rats to the environment previously paired with foot shock induced marked freezing behavior, which was reduced by the anxiolytic diazepam (0.1-3 mg/kg, p.o.) or antidepressants, desipramine and imipramine (10-100 mg/kg, p.o.). Perospirone at 0.3-3 mg/kg, p.o. significantly attenuated the CFS-induced freezing behavior in a dose-dependent manner, while the effect was reduced at the higher dose of 6 mg/kg. Other SDA-type antipsychotics, clozapine (1-30 mg/kg, p.o.) and risperidone (0.03-1 mg/kg, p.o.), and selective 5-HT2 antagonists, ritanserin (0.1-1 mg/kg, p.o.) and ketanserin (0.3-1 mg/kg, p.o.), all reduced the freezing behavior with U-shaped dose-response curves. However, neither conventional antipsychotic, haloperidol (0.1-3 mg/kg, p.o.), chlorpromazine (3-100 mg/kg, p.o.), thioridazine (3-100 mg/kg, p.o.), mosapramine (3-100 mg/kg, p.o.) nor tiapride (30-1000 mg/kg, p.o.) reduced the CFS-induced freezing behavior. In addition, subacute treatment of rats with perospirone (1-10 mg/kg/day) or imipramine (30 mg/kg/day) for 2 weeks prevented the induction of the freezing behavior by CFS. These findings suggest that SDA-type antipsychotics including perospirone are effective for the treatment of mood disturbances such as anxiety and depressive mood associated with schizophrenia and have a broader efficacy profile as compared with the conventional antipsychotics.

Effects of subchronic treatments with SM-9018, a novel 5-HT2 and D2 antagonist, on dopamine and 5-HT receptors in rats

1. Receptor binding and behavioral studies were performed to compare the effects of subchronic treatments with SM-9018, a novel 5-HT2 and D2 antagonist, and with haloperidol (HAL) on dopamine and 5-HT receptors in rats. 2. SM-9018 treatment (10 mg/kg/day p.o.) for 2 weeks did not significantly change the density (Bmax) of striatal D2 receptors or the incidence of stereotyped behavior induced by apomorphine (APO). By contrast, HAL treatment (3 mg/kg/day p.o., for 2 weeks) significantly increased the D2 receptor density by about 55% and markedly enhanced the behavioral response to APO. 3. The density of 5-HT2 receptors in the cerebral cortex was significantly reduced (about 20%) by SM-9018 treatment without being affected by HAL. However, the hyperthermic response of rats to p-chloroamphetamine (p-CAMP, a putative 5-HT releaser) was unaltered by either treatment. 4. Neither SM-9018 nor HAL treatment changed the density of 5-HT1A receptors in the hippocampus. 5. These findings suggest that SM-9018 is weaker than HAL in inducing up-regulation and supersensitivity of the striatal D2 receptors after the subchronic treatment.