Dissociation of head twitches and tremors during the study of interactions with 5-hydroxytryptophan in mice.

Intraperitoneal injection of 5-hydroxytryptophan and 5-methoxy-N,N-dimethyltryptamine is shown to provoke characteristic behaviors in mice that can be quantified. The two principal phenomena described here are head twitches and tremors. Tremors became more frequent when doses of the two substances studied were increased. Head twitches appeared at lower doses, but beyond a certain dose, they decreased and even disappeared. The effects on these movements of agents that modify serotonin function were then studied. The results pose problems of interpretation that are discussed.