Reflex discharges into thoracic white rami elicited by somatic and visceral afferent excitation

Abstract

1. Reflex discharges in white rami (WR) were elicited by single-shock stimulation of dorsal roots (DR), splanchnic (SPL) and intercostal nerves (IC).2. The reflexes have been compared in anaesthetized cats with intact neuraxis, after mid-brain transection and after high cord transection. The brain stem can maintain moderate inhibition of the WR responses, but strong inhibition of IC responses. After cord transection all reflexes are released again.3. Stimulation of ventromedial medullary reticular substance could completely, and independently, inhibit maximal SPL-to-WR and IC-to-WR reflexes.4. Carotid sinus distension did not reduce WR responses, indicating that the major part of the volley is not in vasoconstrictor fibres.5. Central delay of DR-to-WR responses is longer than delay of DR-to-IC responses and is unchanged by transections of the neuraxis at mid-brain or high spinal levels.6. There was no facilitation of WR responses by a prior conditioning volley in the visceral or somatic afferent pathway in contrast to early facilitation of the IC responses.