164 



DONALD M. MAYNARD 



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Fig. 18. Inhibition of spontaneous burst activity {Honianis). a through e form a 

 continuous record: CG, trace from cardiac gangUon ; DN, trace from dorsal nerve. 

 Spikes in DN and between burst in CG represent spontaneous activity in the 

 inhibitor fiber. Note that these are absent in E after high-frequency stimulation 

 during inhibition. Arrows in b indicate first response of inhibitor to stimulation. 

 Large deflection in DA' trace immediately before each inhibitor response to stimu- 

 lation probably represents activity in muscle surrounding the pericardial cavity. 

 The burst frequency and duration decrease during inhibition. There is also 

 evidence of adaptation and post-inhibitoiy excitation. Stimulation frequency, 

 20/sec (Maynard, 1954). 



Burst frequency and impulses per burst are reduced, but the initial maximum 

 impulse frequency seems unaffected or perhaps potentiated by inhibition. 

 Similar patterns have been found in a nuinber of preparations, so relative 

 stability of maximum discharge frequency in followers, while not universal, 

 is by no means unique. It is tempting to ascribe the frequency potentiation 

 to excitatory effects of the inhibitor fiber (compare Fig. 15), but it could 

 equally well result from alterations in the input pattern from other ganglion 



