i52 



DONALD M. MAYNARD 



only one of the four large anterior cells remains active, firing in a regular 

 run. Upon stimulation of one inhibitor fiber, an initial inhibition is followed 

 by recovery or adaptation which eventually levels off at some inhibition 

 plateau (Figs. 6 and 7). In some preparations, adaptation may continue as 

 long as 20 sec, but is usually much briefer. When inhibitory stimulation is 

 stopped, a rebound or post-inhibitory excitation occurs. Both the degree of 

 inhibition and the extent of the rebound depend upon the frequency of 

 inhibitor activity. 



Figure 8 shows that with brief trains, both the number and frequency of 

 impulses affect inhibition. At 50/sec, at least three inhibitory impulses may 

 be necessary before any inhibition of the driven burst is apparent. Frequencies 

 below 5-10/sec usually have little effect on spontaneous burst discharges, 

 but complete inhibition may occur at frequencies of 60-70/sec (Maynard, 

 1953). 



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A 



B 



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D 



Fig. 6. Inhibition of an isolated, spontaneously active large cell (Panulinis). 

 A through D form a continuous record: a, normal activity; b, inhibitory stimulus 

 artifact after the first spike, inhibition of spontaneous activity; c, single impulse 

 during inhibition (adaptation) (there is an increase in frequency, post-inhibitory 

 excitation, at the end of inhibition); d, return to normal activity. The diagram 

 represents the cardiac ganglion (dotted portion has been removed), dorsal 

 nerve and inhibitor nerve. Stimulating electrodes are on one inhibitor nerve, 

 recording electrodes are on the anterior portion of the cardiac ganglion. 

 Inhibitor stimulation frequency, 50/sec; time signal, 60/sec; time line, 01 sec 



(Maynard, 1954). 



