Abolition of ventilatory response to inhaled CO2 by neurological lesions

Abstract

Evidence is presented for the localization of central chemoreceptors. Respiratory minute volume was measured in rats after surgical procedures that removed known or presumed chemoreceptor areas in various combinations. In each case the control ventilation was measured during inhalation of 100% O2, and the test response was the steady state ventilation on breathing O2 with either 5% or 10% CO2 added. To test completeness of carotid chemoreceptor denervation, 6–8% O2 in N2 was employed. Our data show that ventilatory response to inhaled CO2 is abolished if three lesions are produced simultaneously. The lesions must destroy the carotid chemoreceptor, a region surrounding and including the area postrema in the medulla, and diencephalic tissue rostral to a line passing through the posterior commissure dorsally and just behind the optic chiasm ventrally. If any of the three remains intact the ventilatory response is indistinguishable from that of the anesthetized, unoperated control animal. Minute volume is not abnormally low in the CO2-insensitive animal, and superficially the respiratory pattern is of normal rate and depth. A speculative hypothesis regarding the mechanism of function of the non-neural tissue of the area postrema is proposed.