EFFECT ON BREATHING OF NEURONAL DYSFUNCTION IN THE CAUDAL VENTRAL MEDULLA OF GOATS

It has been reported that the caudal ventrolateral medulla (VLM) is im portant in central chemoreception and the control of breathing. The ob jective of this study was to determine in adult goats the effects on b reathing of neuronal dysfunction of this caudal VLM region (area L; ca udal to rostral hypoglossal nerve rootlet). Thermodes were chronically implanted on the VLM to cool neurons and thereby cause neuronal dysfu nction. During awake and (halothane) anesthetized states, cooling the caudal VLM for 20 s to 20 degrees C did not alter breathing (P > 0.10) . However, between 20 and 30 s of cooling and during recovery from coo ling 0-4 mm caudal to the rostral hypoglossal rootlet, there was a 12 (awake) to 25% (anesthetized) increase (P < 0.05) in breathing. This t achypneic hyperpnea was uniform over conditions of eucapnia, hypercapn ia, and hypoxia and resulted from reduced inspiratory time that increa sed frequency. We conclude that in goats inhibitory neurons are locate d in area L and the lateral caudal ventral medulla.