Evidence of a functional role in lung inflation for the buccal pump in theagamid lizard Uromastyx aegyptius microlepis

This study has demonstrated that the agamid desert lizard Uromastyx aegypti us microlepis ventilates its lungs both with a triphasic, thoracic aspirato ry 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 inflat ion arising from thoracic and buccal ventilation was confirmed by direct re cording of volume changes using a whole-body plethysmograph. This observati on was further confirmed by mechanical separation of the inflationary press ures associated with these two breathing mechanisms, enabling the effects o f 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 assoc iated 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 CO 2. This study describes two lung-inflation mechanisms (an amphibian-like bu ccal pump and a mammalian-like aspiration pump) in a single extant amniote, both of which are subject to vagal feedback control.