Evidence of a Functional Role in Lung Inflation for the Buccal Pump in the Agamid Lizard Uromastyx Aegyptius Microlepis

Abstract

This study has demonstrated that the agamid desert lizard Uromastyx aegyptius microlepis ventilates its lungs both with a triphasic, thoracic aspiratory pump and by gulping air, using a buccal pump. These two mechanisms never occur simultaneously because bouts of buccal pumping are always initiated after the passive expiration that terminates a thoracic breath. Lung inflation arising from thoracic and buccal ventilation was confirmed by direct recording of volume changes using a whole-body plethysmograph. This observation was further confirmed by mechanical separation of the inflationary pressures associated with these two breathing mechanisms, enabling the effects of lung inflation on buccal breathing to be observed. This revealed that the buccal pump is influenced by a powerful Hering-Breuer-type reflex, further confirming its role in lung inflation. Bilateral thoracic vagotomy tended to increase the variance of the amplitude and duration of the breaths associated with the aspiration pump and abolished the effects of lung inflation on the buccal pump. Uromastyx has vagal afferents from pulmonary receptors that respond to changes in lung volume and appear not to be sensitive to CO2. This study describes two lung-inflation mechanisms (an amphibian-like buccal pump and a mammalian-like aspiration pump) in a single extant amniote, both of which are subject to vagal feedback control.