Involvement of alpha-adrenoceptors in para-hydroxyamphetamine-induced head-twitch response

The effect of some drugs with a higher selectivity for either the alpha 1- or alpha 2-adrenoceptors on the head-twitches induced by intracerebroventricular administration of p-hydroxyamphetamine (p-OHA) in mice, have been studied. Pretreatment with yohimbine increased the number of head-twitches induced by p-OHA, whereas pretreatment with clonidine or prazosin reduced the number of responses. The decrease in head-twitches produced by clonidine was completely antagonized by pretreatment with yohimbine. Pretreatment with 6-hydroxydopamine prior to the combined treatment with clonidine and p-OHA, resulted in recovery of the reduced level head-twitches to the level induced by p-OHA alone. Pretreatment with 6-hydroxydopamine alone resulted in a marked increase in the number of p-OHA-induced head-twitches. These results clearly indicate that a noradrenaline system in the brain may, at least in part, be involved in the p-OHA-induced head-twitches in mouse, most probably by modulating a serotonergic system which is responsible for the head-twitch response.