Effects of TRH on the central nervous system of the rabbit

Thyrotropin releasing hormone (TRH) administered intraventricularly to rabbits produces tachypnea, hyperthermia, behavioral excitation and, with larger doses, compulsive scratching. These effects of TRH were unaffected by various catecholamine and serotonin antagonists or depleting agents. When TRH was administered to pentobarbital-narcotized animals, tachypnea and rapid recovery of the righting reflex occurred. The antagonism of narcosis or sedation was evident against other barbiturates, diazepam, chlorpromazine, and reserpine, but not against morphine. Morphine actually appeared to antagonize the excitatory actions of TRH. Scopolamine pretreatment prevented the arousal from pentobarbital narcosis, but not the tachypnea or hyperthermia. TRH represents a new class of psychoactive chemical which may play a role in brain function.