Effect of L-histidine pretreatment on haloperidol induced catalepsy and ethamphetamine stereotypy in mice

. Pretreatment with L-histidine, precursor of histamine, was found to potentiate haloperido1 induced catalepsy and to antagonise methamphetamine stereotypy while pretreatment with chlorcyclizine, a H1-receptor blocker, was found to antagonise haloperidol catalepsy and to potentiate methamphetamine stereotypy: Further, chlorcyclizine was found to antagonise the potentiating effect of L-histidine on haloparidol catalepsy and also the inhibitory effect of L histidine on methamphetamine stereotypy. Our results indicate that the central histaminergic system by exerting a modulatory influence on the striatal dopaminergic system may influence the functioning of the extrapyramidal motor system.