Effects on respiratory pattern of focal cooling in the medulla of the dog

Abstract

Studies in cats have shown that, in addition to respiratory neuron groups in the dorsomedial (DRG) and ventrolateral (VRG) medulla, neural structures in the most ventral medullary regions are important for the maintenance of respiratory rhythm. The purpose of this study was to determine whether a similar superficially located ventral region was present in the dog and to assess the role of each of the other regions in the canine medulla important in the control of breathing, in 20 anesthetized, vagotomized, and artificially ventilated dogs, a cryoprobe was used to cool selected regions of the medulla to 15-20 degrees C. Respiratory output was determined from phrenic nerve or diaphragm electrical activity. Cooling in or near the nucleus of the solitary tract altered timing and produced little change in the amplitude or rate of rise of inspiratory activity; lengthening of inspiratory time was the most common timing effect observed. Cooling in ventrolateral regions affected the amplitude and rate of rise of respiratory activity. Depression of neural tidal volume and apnea could be produced by unilateral cooling in two ventrolateral regions: 1) near the nucleus ambiguus and nucleus para-ambiguus and 2) just beneath the ventral medullary surface. These findings indicate that in the dog dorsomedial neural structures influence respiratory timing, whereas more ventral structures are important to respiratory drive.

A single minute lesion around the ventral respiratory group in medulla produces fatal apnea in cats

“…century Wang, 1980 , and the region around the ventral Ž . respiratory group VRG of the medulla has been found to Ž be the site most important for such action Adams et al, 1988;Feldman and Smith, 1989;Onimaru et al, 1989;. Onimaru, 1995;Paton et al, 1994 . We have observed that Ž .…”

“…Ž . Adams et al 1988 reported that in dogs, insertion of a cryoprobe needle into the ventral and dorsal respiratory group for cooling the medulla often produced respiratory distress.…”