[An experimental study on the inhibitory response of the frog semicircular canal nerve]

The inhibitory response of the posterior semicircular canal (p.s.c.) ampullary nerve was studied in comparison with the excitatory response. The isolated p.s.c. of the bull frog was stimulated by the mechanical endolymphatic flow toward either the ampullofugal (AF, excitatory) or the ampullopetal (AP, inhibitory) direction. Three experiments were performed. 1) Experiment I: The influence of the endolymphatic K+ concentration. In both the high (50mM) and the low (2.5mM) K+ environment, the inhibitory response was smaller than the excitatory response. This was more pronounced in the low K+ environment. 2) Experiment II: The influence of the initial position of the cupula. The magnitudes of the responses when the cupula was moved from various positions were compared. When the same amount of stimulus was given in the same direction, the responses were equal regardless of the initial position of the cupula. The inhibitory response yielded a time constant approximately 2-3 times as long as the excitatory response. 3) Experiment III: The interaction of the AF and the AP stimulus. The influence of the inhibitory response upon the following excitatory response and vice versa, were studied by changing the timing of the stimulus onset. Both the action potential and the DC potential were recorded for comparison. The AP stimulus which immediately followed the AF stimulus suppressed the action potential and the negative DC potential was observed. On the other hand the AF stimulus which immediately followed the AP stimulus gave rise to the distinct positive DC potential but the action potential could hardly be evoked. That AF stimulus resulted in different responses between the action potential and the DC potential indicates that the DC potential recorded in this study is possibly a generator potential.