Behavioral studies of shaking behavior induced by thyrotropin-releasing hormone and morphine withdrawal in rats

A behavioral study was performed in an attempt to understand the neuronal mechanisms involved in wet dog body shaking in rats induced by the administration of thyrotropin-releasing hormone (TRH). The body shaking evoked by TRH (10 mg/kg, i.p.) was not affected by pretreatment with methysergide, scopolamine, levallorphan or phentolamine, but was inhibited by clonidine, haloperidol and reserpine. Body shaking behavior was also elicited by injection of levallorphan to morphine-dependent rats. The morphine-withdrawal body shaking was antagonized by pretreatment with TRH in the doses (10, 20 mg/kg, i.p.) which alone induced body shaking. A dose of TRH (10 mg/kg, i.p.) which induces body shaking in control rats, was without effect in morphine-dependent rats that had undergone withdrawal. The present results imply that TRH-induced body shaking is not associated with the increased activity of serotonergic, cholinergic and enkephalinergic neurons in the brain, and also its mechanisms seem to be different from that of morphine-withdrawal body shaking.