Cardiovascular and respiratory responses from local heating of medulla oblongata

Abstract

The lower brain stem was explored for cardiovascular and respiratory responses by means of local diathermy in 36 urethane-anesthetized and 48 unanesthetized, decerebrate cats. In the lateral reticular formation, extending from the level of the rostral end of the inferior olivary nuclei to the most caudal portion of the medulla oblongata, localized heating decreased both rate and tidal volume of respiration, with marked bradycardia, a slight change in systolic blood pressure, and some increase in pulse pressure. Electrical stimulation of the same area usually induced forceful inspiration associated with no cardiovascular response. The thermally induced bradycardia, but not the decrease of respiration, was abolished by vagotomy or by the administration of atropine. The same diathermy applied locally to the rostral hypothalamus in the same cats evoked mainly acceleration of respiration with little cardiovascular reaction. The present experiments suggest that the lateral reticular formation of the medulla is as sensitive to thermal stimulation as is the rostral hypothalamus. The significance of the medullary thermal sensitivity, however, is not clear.