CHEMORECEPTOR-SENSITIVE NEURONS IN COMMISSURAL SUBNUCLEUS OF NUCLEUS-TRACTUS-SOLITARIUS OF THE RAT

Experiments were carried out in pentobarbital-anesthetized, vagotomize d, paralyzed, and artificially ventilated male Wistar rats with a pneu mothorax. Blood pressure, heart rate, and phrenic nerve activity were recorded. Extracellular neuronal recordings were made by glass micropi pettes in a midline area in the commissural subnucleus of the nucleus tractus solitarius. At the end of the experiment, the recording sites were marked. Chemoreceptors were stimulated by tracheal administration of N-2 or injection of CO2-saturated saline (50 mu l) near the caroti d body. The baroreceptors were stimulated by an intravenous injection of phenylephrine (1-3 mu g). Neurons that were excited by chemorecepto r stimulation but not baroreceptor stimulation were found in the commi ssural subnucleus of nucleus tractus solitarius and were designated as chemoreceptor-sensitive neurons. They exhibited a continuous discharg e (9.9 +/- 1.3 spikes/s) that showed no apparent relation to either ph renic nerve bursts or arterial pulses. Such neurons were not found in the rostral portions of the nucleus tractus solitarius. These results confirm and extend our previous reports in which a discrete chemorecep tor projection site was identified in the commissural subnucleus of th e rat.