AFFERENT CONTRIBUTIONS TO INTERMEDIATE AREA OF THE CAT VENTRAL MEDULLARY SURFACE DURING MILD HYPOXIA

The intermediate area of the cat ventral medullary surface activates t o mild hypoxia. Carotid body and vagal afferent contributions to this response were examined by recording activity levels, measured as chang es in scattered 660 nm light, from the medullary surface in 7 anesthet ized, spontaneously breathing cats following 12% O-2 in N-2 ventilator y challenge. A miniaturized video camera collected images synchronous with the,peak of cardiac R wave at 1/s, from a 3.2 mm diameter area, b efore, and following bilateral carotid sinus denervation (CSD) and vag otomy. In intact animals, hypoxia increased activity; however, greater increases in activity levels followed CSD, while vagotomy elicited a marked reduction of the response. Thus, carotid body afferents exert i nhibitory or disfacilitatory influences on intermediate area neurons, while the vagus appears to play an excitatory role.