SPATIOTEMPORAL ASPECTS OF SYMPATHETIC C-FIBER AFFERENT ACTIVITY IN PRESSOR REFLEX DURING ABDOMINAL ISCHEMIA

Activation of abdominal sympathetic visceral afferents during ischemia elicits excitatory cardiovascular reflexes. The present study examine d the time course and discharge patterns of activation of ischemically sensitive sympathetic C-fiber afferents, and then the relationship be tween summated afferent activity and the presser reflex induced by pro longed abdominal ischemia was determined. Single-unit activity of abdo minal C-fiber afferents was recorded from the right thoracic sympathet ic chain of anesthetized cats during 30 min of ischemia. The reflex pr esser response to abdominal ischemia was induced by occlusion of celia c and superior mesenteric arteries. Of 68 C-fiber afferents studied, 3 6 (similar to 53%) were activated during 30 min of ischemia, whereas t he activity of the remaining 32 were not altered. Onset latencies of 3 6 C-fiber afferents activated by ischemia ranged from 1.0 to 17.4 min with an average of 6.1 +/- 0.8 min. The majority of activated afferent s manifested a bursting pattern of discharge activity as ischemia was prolonged beyond 10 min. Summated response of activated afferents, but not individual afferent activity, was related closely to the reflex p resser response during 30 min of ischemia. These results suggest that both recruitment of sufficient numbers of C-fiber afferents and adequa te discharge frequency of afferents constitute an encoding mechanism f or the presser reflex during abdominal ischemia.