Effects of triiodothyronine on the 5-hydroxytryptophan-induced head twitch and its potentiation by antidepressants in mice.

Daily injection of triiodothyronine (T3) for 3 consecutive days dose dependently enhanced 1-5-HTP (4 mg/kg)-induced head twitches in mice. This effect was blocked by 1-penbutolol. Pretreatment with a sub-effective dose of T3 (0.06 mg/kg) markedly enhanced the ability of clenbuterol but not indalpine to potentiate the response to 1-5-HTP. Likewise, the effects of T3 were more pronounced on the desipramine- or maprotiline-induced potentiation of head-twitches than on the action of citalopram or clomipramine. These data suggest that the increased responsiveness to 1-5-HTP caused by T3 involves an indirect (noradrenalin-mediated) rather than a direct effect on serotonergic processes.