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 examined the time course and discharge patterns of activation of ischemically sensitive sympathetic C-fiber afferents, and then the relationship between summated afferent activity and the pressor reflex induced by prolonged abdominal ischemia was determined. Single-unit activity of abdominal C-fiber afferents was recorded from the right thoracic sympathetic chain of anesthetized cats during 30 min of ischemia. The reflex pressor response to abdominal ischemia was induced by occlusion of celiac and superior mesenteric arteries. Of 68 C-fiber afferents studied, 36 (approximately 53%) were activated during 30 min of ischemia, whereas the activity of the remaining 32 were not altered. Onset latencies of 36 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 afferents 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 pressor response during 30 min of ischemia. These results suggest that both recruitment of sufficient numbers of C-fiber afferents and adequate discharge frequency of afferents constitute an encoding mechanism for the pressor reflex during abdominal ischemia.