Influence of different histamine receptor agonists and antagonists on apomorphine-induced licking behavior in rat

Abstract

The effects of different histamine receptor agonists and antagonists on apomorphine-induced licking behavior in rats were investigated. Subcutaneous (s.c.) injection of various doses of apomorphine (0.125–1.25 mg/kg) induced licking. The licking response was counted by direct observation and recorded for a 75-min period. Intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of the histamine H 1 or H 2 receptor agonist, HTMT (6-[2-(4-imidazolyl)ethylamino]- N-(4-trifluoromethylphenyl) heptanecarboxamide) (50 and 100 μg per rat), or dimaprit (10 and 15 mg/kg, i.p.), respectively, potentiated apomorphine-induced licking, while the histamine H 3 receptor agonist, imetit (5 and 10 mg/kg, i.p.), reduced the licking response induced by apomorphine. Pretreatment with various histamine receptor antagonists, dexchlorpheniramine (30 and 40 mg/kg, i.p.), diphenhydramine (20, 30 and 40 mg/kg, i.p.), famotidine (30 and 40 mg/kg, s.c.) and ranitidine (20, 30 and 40 mg/kg), reduced apomorphine-induced licking, while thioperamide (5 and 10 mg/kg, i.p.) potentiated the apomorphine effect. The effects of HTMT and dimaprit were blocked by dexchlorpheniramine (20 mg/kg, i.p.) and famotidine (20 mg/kg, s.c.), respectively. The inhibitory effect elicited by imetit on apomorphine-induced licking behavior was also abolished in animals treated with thioperamide (2.5 mg/kg, i.p.). The results suggest that histaminergic mechanisms may be involved in the modulation of apomorphine-induced licking behavior.