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

Background and Repetitive licking behaviour is a stereotyped phenomenon that is correlated with activation of the nigrostriatal system, and is thought to be produced by activation of both postsynaptic dopamine D1 and D2 receptors. There are good evidences showing that the histaminergic mechanisms may be closely related to dopaminergic systems, and play an important modulatory role in various behaviours induced by dopaminergic agents. Ïn order to clarify the possible role of the histaminergic mechanism(s) in the modulation of licking behaviour, the effects of several histamine receptor agonists and antagonists were studied on the licking behaviour induced by apomorphine in the rat. 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 period of 75 min. Ïntracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of the histamine H1 or H2 receptor agonists, HTMT (50 and 100 μg per rat), or dimaprit (10-15mg/kg, i.p.), respectively, potentiated apomorphine-induced licking, while imetit (5 and 10 mg/kg, i.p.), reduced the licking response. Pretreatment with various histamine receptor antagonists, dexchlorpheniramine, diphenhydramine, famotidine and ranitidine reduced apomorphine-induced licking, while thioperamide potentiated the apomorphine effect. The effects of HTMT and dimaprit were blocked by dexchlorpheniramine and famotidine respectively. The inhibitory effect elicited by imetit was also abolished with thioperamide. Çonclusion: The results suggest that histaminergic mechanisms may be involved in the modulation of apomorphine-induced licking behaviour.