Neurophysiological studies on central chemosensor in medullary ventrolateral areas

Nonphasic unit potentials were recorded with glass microelectrodes from the ventrolateral medullary areas in spontaneously breathing cats. The firing rate changes were studied during metabolic acidosis and alkalosis induced by intravenous injections of 4 ml 0.1 N HCl and molar NaHCO3, respectively, and during CO2 rebreathing. Three groups of units were distinguished among 44 neurons: 1) 9 U were markedly sensitive to variations in acid-base parameters; each reacted in the opposite manner upon acidosis and alkalosis, and these reactions were reproducible. 2) Twelve units were responsive to touch of a contralateral limb with a prompt and massive rise in firing rate. 3) The remaining 23 U were classified as nonsensitive to any of the stimuli applied. All these 44 U were found to be intermingled. It is possible that the chemosensitive cells found may be part of the central chemosensor.