Intrapulmonary CO 2 inhibits inspiration in garter snakes

Abstract

This study was undertaken to assess the role of intrapulmonary chemoreceptors in the control of breathing in reptiles. Garter snakes were thracheostomized to remove the influence of upper airway receptors. After recovery from anesthesia, the animals were unidirectionally ventilated or allowed to ventilate normally, but without glottal control of the breath-hold. Breathing movements were recorded by means of a pneumotachograph. When a bidirectionally breathing snake was presented with CO 2 at the tracheal tube, inspiratory duration and volume decreased. When CO 2 was removed from the inspired air between breaths, inspiratory duration and volume increased. Removing CO 2 from the airstream of a unidirectionally ventilated snake during a breath-hold produced apnea, but removing CO 2 at the beginning of inspiration caused the duration and volume of the inspiration to increase. This reflex appears to represent a positive feedback mechanism for enhancing inspiration once a breath has been initiated.