The pattern of respiratory nerve activity in the bullfrog

The electrical activity of the cranial nerves innervating the muscles which contract and dilate the buccal cavity (defined BCcont and BCdil, respectively) was explored in the bullfrog, Rana catesbeiana. The sternohyoid branch of the hypoglossal nerve innervating BCdil showed electrical activity in two consecutive phases: buccal inhalation and lung expiration as well as in the last phase of the pulmonary ventilatory cycle. The last phasic activity was apparently identical to the first one of the succeeding cycle when the cycles were repeated consecutively. The nerves innervating BCcont, consisting of the Vth, VIIth, IXth, Xth, and XIIth cranial nerves, generally showed two consecutive phasic activities in the period of lung expiration and lung inspiration. Thus the present result indicated that during three consecutive phases of the pulmonary ventilatory cycle, the nerve for BCdil was active in the first two phases, and the nerves for BCcont in the last two phases. In both nerve activities the magnitude of the integrated peak activity was smaller in the preceding than in the later phase. In the buccal oscillation cycle, the nerve for BCdil was active during pressure depression while the nerves for BCcont were active during pressure elevation in the buccal cavity. The nerves for both mouth closing and that for tongue retraction had phasic activity during respiratory cycles.