Abstract
Aquatic frogs, Pipidae have some interesting characteristics from the viewpoint of comparative respiration physiology. They lack buccal ventilatory cycle, exhale air from the lung before aspirating air into the buccal cavity, and have inherent muscles suspected homologous to the mammalian 'diaphragm'. To study the reason why the aquatic frogs lack the buccal cycle, we recorded the respiratory motor outputs from the in vitro brainstem preparation of Xenopus laevis excluding the influence by the peripheral feedback mechanisms. The cranial nerve activities of the Xenopus exhibited the intermittent bursts with doublet, triplet or multiplet patterns, those were similar to the lung-breathing pattern in vivo, and lacked the rapid bursting activity corresponding to the buccal oscillation. The activation sequence of motor outputs within a burst complex was consistent with that of the normal ventilation in vivo. These results indicate that the intermittent pattern and the lack of buccal oscillation in the breathing of Xenopus are not caused by reflex mechanism but generated within the brainstem. This in vitro preparation may be useful for the comparative study as a model close to the ancestor of amiotes. [J Physiol Sci. 2008;58 Suppl:S117]
