Factors affecting the onset and termination of respiration in the salamander, Amphiuma tridactylum.

Abstract

Respiratory control was studied in 22 intact, free-swimming Amphiuma tridactylum. Termination of inspiration was shown to be controlled by a volume-detection mechanism. Animals were shown to continue the breathing process if air was simultaneously removed from the lungs through a lung cannula. Injections of nitrogen into the lungs terminated inspiration for a short time but breathing occurred a short time after. Carbon dioxide injected into the lungs in doses 3-5 times the concentration normally present was removed from the lungs rapidly and did not result in the onset of breathing if the oxygen tensions were sufficiently high. Very high concentrations of carbon dioxide in the lungs resulted in a shortening of time between breaths. Increased levels of carbon dioxide in the dorsal aorta did not bring about the breathing response. Removal of oxygen from the lungs brought about a rapid breathing response. The presence of an oxygen chemoreceptor was postulated as a mechanism for controlling breathing in Amphiuma.