CARDIAC INHIBITION IN DECAPOD CRUSTACEA 



153 



Ficj. 7. Isolated large cell, time course of inhibition. (/'fl/;///;V».v, same preparation as 

 Fig. 6.) Ordinate, spontaneous activity of ganglion neuron; abscissa, time in 

 seconds. The effect of three ditTerent stimulation frequencies is shown: 18/sec, 

 23/sec, and 33/sec. Cessation of inhibitory stimulation is marked by end. Tempera- 

 ture is about 25 C (Maynard, 1954). 



Post-inhibitory Events 



Latent pause. The latent pause is the interval between the end of inhibitor 

 activity and the first post-inhibitory discharge. Its duration increases with 

 the effectiveness of the preceding inhibition, but decreases with the duration 

 of inhibitor activity and the time since the preceding discharge (Fig. 9). 

 The increase of the latent pause with inhibition suggests a residual depression 

 that ordinarily may be masked by rebound effects. This is illustrated by the 

 preparation shown in Fig. 10 which is driven by an electrical stimulus imme- 

 diately following a train of inhibitory stimuli adequate for complete inhibi- 

 tion but too brief to induce rebound. As indicated by prolonged latencies, 

 the driven response may show residual inhibition for 0-75 sec after the end 

 of inhibitory stimulation. If such a brief inhibitory train is given to a normal 

 spontaneous preparation, its effectiveness depends upon its position in the 

 interburst period. The later in the period the greater the inhibition but the 

 shorter the latent pause, and vice versa. 



Rebound. Post-inhibitory rebound increases with high-frequency inhibitor 

 activity, and for the first 5-10 sec, with prolongation of inhibition. After 



