Proportional inhibition in the cricket medial giant interneuron.

Inhibitory effects on the number of wind-evoked impulses were studied in the medial giant interneuron of the cricket, Gryllus bimaculatus. The interneuron receives an inhibitory input from wind receptors on cercus ipsilateral to its soma. Using a dual channel wind stimulator, the intensity of inhibitory input was changed over 1,000-fold and effects on the number of spikes were observed. The ipsilateral inhibition reduced the number of outgoing spikes from a level elicited by excitation alone and it did so in proportion to the level of wind responsiveness displayed by each cell. A proportional coefficient of inhibition was derived and its value depended on the level of total excitation of the medial giant interneuron. The medial giant interneurons with high excitation showed a smaller value of the coefficient than those with low excitation. The proportional inhibition of the medial giant interneuron by the ipsilateral cercus suppresses the number of its spikes to a reasonable level for a wide range of stimulus intensities under natural conditions.