Antipsychotic-like profile of thioperamide, a selective H3-receptor antagonist in mice

Experimental and clinical evidence points to a role of central histaminergic system in the pathogenesis of schizophrenia. The present study was designed to study the effect of histamine H-3-receptor ligands on neuroleptic-induced catalepsy, apomorphine-induced climbing behavior and amphetamine-induced locomotor activities in mice. Catalepsy was induced by haloperidol (2 mg/kg p.o.), while apomorphine (1.5 mg/kg s.c.) and amphetamine (2 mg/kg s.c.) were used for studying climbing behavior and locomotor activities, respectively. (R)-alpha-methylhistamine (RAMH) (5 mu g i.c.v.) and thioperamide (THP) (15 mg/kg i.p.), per se did not cause catalepsy. Administration of THP (3.75, 7.5 and 15 mg/kg i.p.) 1 h prior to haloperidol resulted in a dose-dependent increase in the catalepsy times (P < 0.05). However, pretreatment with RAMH significantly reversed such an effect of THP (15 mg/kg i.p.). RAMH per se showed significant reduction in locomotor time, distance traveled and average speed but THP (15 mg/kg i.p.) per se had no effect on these parameters. On amphetamine-induced hyperactivity, THP (3.75 and 7.5 mg/kg i.p.) reduced locomotor time, distance traveled and average speed (P < 0.05). Pretreatment with RAMH (5 mu g i.c.v.) could partially reverse such effects of THP (3.75 mg/kg i.p.). Climbing behavior induced by apomorphine was reduced in animals treated with THP. Such an effect was, however, reversed in presence of RAMH. THP exhibited an antipsychotic-like profile by potentiating haloperidol-induced catalepsy, reducing amphetamine-induced hyperactivity and reducing apomorphine-induced climbing in mice. Such effects of THP were reversed by RAMH indicating the involvement of histamine H-3-receptors. Findings suggest a potential for H-3-receptor antagonists in improving the refractory cases of schizophrenia.