Medullary unit responses to changes in local and hypothalamic temperatures in the cat

Single unit activity was recorded with glass microelectrodes in the reticular formation of the medulla oblongata of cats lightly anesthetized with urethan, while medullary temperature was changed by surface irrigation with warm or cold artificial cerebrospinal fluid. In addition, water-perfusion thermodes were implanted over the preoptic anterior hypothalamus (POAH) region, and the effects of heating and cooling of the POAH on firing rate of medullary units were studied. One hundred and twenty-five temperature-sensitive neurons were studied in the medullary reticular formation. Out of these 125 neurons, 80 were warm-sensitive and 45 were cold-sensitive. Sixteen warm-sensitive medullary neurons were examined in responses to changes of POAH temperature. Ten units (62.5%) responded, and the remaining 6 units were not responsive to changes of the POAH temperature. Of 13 cold-sensitive neurons examined, 10 units (77.0%) responded. On the other hand, only 1 out of 7 (14.3%) temperature-insensitive neurons tested did respond to changes in the POAH temperature. These results suggest that the temperature signals sent out from thermosensitive structures in the hypothalamus might be transmitted to a major portion of temperature-sensitive neurons in the medullary reticular formation.