Ventral medullary surface inputs to cervical sympathetic respiratory oscillations

Abstract

To examine the effects of focally cooling three areas (rostral, intermediate, and caudal) of the ventral medullary surface (VMS) on respiratory oscillations in cervical sympathetic and phrenic nerve activity, 12 cats were anesthetized, vagotomized, paralyzed, and artificially ventilated with 7% CO2 in O2. Cooling the intermediate area from 37 to 20 degrees C significantly reduced the magnitude of respiratory oscillations in both cervical sympathetic activity (P less than 0.001) and phrenic activity (P less than 0.001). Graded cooling of all three areas caused graded reductions in sympathetic respiratory-related activity that were comparable to the reductions in phrenic activity. The magnitude of the reductions in sympathetic respiratory oscillations was greatest for the intermediate area, followed in order by the caudal and rostral areas. Eight cats also underwent graded VMS cooling while ventilated with 3% CO2 in O2 and 100% O2. At each level of inspired CO2, graded cooling resulted in graded reductions in respiratory oscillations in sympathetic activity; conversely, at each medullary temperature, graded increases in inspired CO2 caused graded increases in cervical sympathetic respiratory activity. These results suggest that all three areas of the VMS influence respiratory oscillations in cervical sympathetic activity, although to different extents.