Tonic immobility in chickens: possible involvement of monoamines.

Tonic immobility in chickens was affected by a variety of drugs that act on monoaminergic systems. Compounds that enhanced the duration of tonic immobility were d-LSD, BOL-148, pargyline, and iproniazid; 5-hydroxytryptophan, p-CPA, and atropine had no effect. Injections of serotonin depressed response duration. A suggestive parallel was noted between the results of the present study and those of previous work reporting drug-induced suppression of raphe electrical activity. The data appear to implicate monoamines, especially serotonin, in the mediation of behavioral activation and suppression.