Trigeminal nerve activity and buccal pressure as an index of total inspiratory activity in the bullfrog.

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Abstract
In bullfrogs with glottis occluded and lungs artificially ventilated, the buccal cavity contractors (BCconts) contracted isometrically, meaning that peak buccal pressure (OBP) well represents the total inspiratory nerve activities (TIA) of BCconts. Unilateral sectioning of the trigeminal (V), hypoglossal, facial or vagal nerve reduced the magnitude of OBP by 43.3, 28.8, 10.9 or 4.3%, respectively. The integrated peak V activity (I-ENGv) showed a linear relationship to OBP (r = 0.944) in the glottis occluded frog, but a curvilinear relationship to peak buccal pressure (peak BP) in the spontaneously breathing frog during inflation period. The latter relationship was better fitted by a hyperbolic equation (r = 0.943) than by a linear equation (r = 0.927) (P < 0.001). The relationship between I-ENGv and peak BP showed a hysteresis during deflation period. Both I-ENGv and peak BP may be used as a measure of TIAs, but use of the latter requires some reservations.