Calibration of Thresholds for Functional Engagement of Vagal A, B and C Fiber Groups In Vivo

Abstract

To establish a simple protocol to define stimulus thresholds for vagal A, B and C fibers. The intact left or right cervical vagus was stimulated with 0.1ms pulses in spontaneously breathing anesthetized rats. Heart and respiratory rate responses to vagal stimulation were recorded. The vagus was subsequently cut distally, and mass action potentials to the same stimuli were recorded. Stimulating at either 50Hz for 2 s or 2Hz for 10 s at experimentally determined strengths revealed A, B and C fiber thresholds that were related to respiratory and heart rate changes. Our simple protocol discriminates vagal A, B and C fiber thresholds in vivo.