Synergistic behavioral effects of serotonin and tryptamine injected intrathecally in mice.

The endogenous compounds, serotonin (5-HT) and tryptamine (TA), have been found to alter function in the CNS, supporting the hypothesis that they serve as neurotransmitters. It is reported here that intrathecal injections of either 5-HT or tryptamine elicited similar behavioral syndromes consisting of caudally-directed biting, or licking and scratching. Serotonin was found to be considerably more potent than tryptamine. However, administration of both indoleamines produced synergistic interactions with respect to this behavioral syndrome. Administration of fluoxetine with either 5-HT or tryptamine potentiated the scratching behavior produced by either indoleamine, but failed to enhance the effect of an injection of 5-HT plus tryptamine. Administration of methysergide blocked the effects of both indolamines. The results are discussed in terms of a possible mechanism of the synergism between 5-HT and tryptamine.