Effect of L-histidine and chlorcyclizine on apomorphine-induced climbing behaviour and methamphetamine stereotypy in mice.

Pretreatment with L-histidine (850 and 1000 mh/kg, i.p.), a precursor of brain histamine, and chlorcyclizine (25 and 50 mg/kg, i.p.), a H1-receptor blocker, failed to modify apomorphine-induced climbing behaviour in mice. In contrast, pretreatment with L-histidine (850 and 1000 mg/kg) was found to antagonise methamphetamine stereotypy while pretreatment with chlorcyclizine (25 mg/kg) was found to potentiate methamphetamine-induced stereotypy in mice. The results suggest that drugs which influence central histaminergic mechanisms are effective only in modifying the behaviour induced by the indirectly acting DA agonist methamphetamine and fail to modify the behaviour induced by apomorphine, a directly acting DA agonist.