Effect of indolealkylamine manipulations on locomotor activity in rats

The effect of various manipulations of the indolealkylamine system upon locomotor activity in adult male rats was investigated. 6-fluorotryptophan, a rapidly acting tryptophan hydroxylase inhibitor, produced a small, but significant decrease in activity. Neither variations in the dietary content of l-tryptophan, nor systemic injections of l-tryptophan had any effect on activity. However, pretreatment with the monoamine oxidase inhibitor, pargyline, caused l-tryptophan injections to produce a syndrome characterized by large increases in activity, tremor, rigidity, hyper-reactivity, streotyped head movements, and a general sympathetic response. Pretreatment with spiroperidol, a presumed specific dopamine receptor blocker, abolished all signs of the syndrome except for the rigidity and hyper-reactivity. By contrast, the noradrenergic receptor blockers, phenoxybenzamine and propanolol, had no observable effect on the syndrome.