Identification by microinjection of TRH-sensitive sites in the cat's brain stem that mediate respiratory, temperature and other autonomic changes.

Cats were prepared with an array of stereotaxically implanted guide tubes, the tips of which rested just above selected structures in the brain stem. Thyrotropin-releasing hormone (TRH) was microinjected in a volume of 0.5 micronl at 347 individual sites scattered throughout the hypothalamus and mesencephalon Polypnea, hypothermia, vocalization, salivation, defecation and vasodilation were evoked by 10-20 ng of TRH injected only at loci in the mesencephalon, principally in the reticular substance. TRH failed to lower body temperature when it was infused at the same sites in the anterior hypothalamus at which norepinephrine produced its characteristic hypothermia. These results suggest that the TRH-induced hypothermia is a secondary effect of tachypnea which results from the action of the tripeptide on the mesencephalic respiratory-autonomic mechanism.