Head twitches produced by serotonergic drugs and opiates after lesion of the mesostriatal serotonergic system of the rat.

Electrolytical lesions of the dorsal raphe nucleus in the rat did not change frequency of head twitches produced by codeine and apocodeine. The action of serotonergic drugs was affected differently: the lesion depressed the frequency of head twitch episodes produced by 5-hydroxytryptophan (5-HTP), LSD and quipazine, but did not change the frequency of head twitches produced by 5-methoxytryptamine. On the other hand, the lesions protected against high mortality produced by combined treatment with tranylcypromine and 5-methoxytryptamine. There was a good correlation between the extent of lesion, measured by the depression of the level of prosencephalic serotonin, and the depression of head twitch frequency produced by 5-hydroxytryptophan and quipazine, while the correlation was not significant for the action of LSD. It is concluded that presynaptic serotonergic structures belonging to the mesostriatal serotonergic system are necessary for appearing of head twitches after treatment with 5-HTP, LSD and quipazine, and therefore these compounds have a presynaptic action in this test.