ROSTRAL VENTRAL MEDULLARY SURFACE-ACTIVITY DURING HYPERCAPNIC CHALLENGES IN AWAKE AND ANESTHETIZED GOATS

Regions within the rostral ventral medullary surface (RVMS) play an im portant role in cardiorespiratory responses to CO2 during anesthesia. Activity within a RVMS area, in which local cooling elicited marked ve ntilatory and blood pressure reductions, was measured as 660 nm scatte red light changes in 5 goats following 5% CO2 challenges during waking and anesthetic states. During wakefulness, hypercapnia elicited a sub stantial, short latency transient (1-1.5 min) activity increase, follo wed by a sustained decrease. Stimulus cessation elicited a large and r apid off-transient activity increase which persisted for similar to 20 min. In contrast, during halothane anesthesia, the initial activation was absent, and the later activity decline and off-response were much reduced. We conclude that biphasic RVMS activity responses emerge to CO2 stimulation, and are state-dependent.