312 



C. EYZAGUIRRE 



Fig. 21. Facilitation of antidromic invasion by inhibitory action. Same cell as in 

 Fig. 20. A (a). Single inhibitory and antidromic (a] ) potential on same sweep (not 

 stimulated together). A(b). (al), (al) at 20msec interval, sweep repetition rate 

 of 5/sec. Full invasion of soma is blocked, a (c). Inhibitory impulse facilitates soma 

 invasion by (a\). b (a). Three inhibitory impulses alone, b (b). (a\), (al) at 5 msec 

 interval, single sweep. («2) is blocked, b (c). Inhibitory stimulation facilitates inva- 

 sion by previously blocked {a2). Time, 100 c/s. (From Kuffler and Eyzaguirre, J. 

 Gen. Physiol. 39 : 155-184, 1955.) 



this current flow (if there are conductance changes in the dendrites) in such 

 a way that part of this current will not reach the soma or that zone of the 

 axon where the impulse has been blocked. This, in itself, will diminish the 

 chances for local, partially conducted impulse activity and it is a good indica- 

 tion that synaptic endings occur over a sizable portion of the dendrites (cf. 

 Kuffler and Edwards, 1958). 



When an inhibitory potential is capable of setting up a depolarization, 

 partial axon-soma transmission block can actually be reheved by inhibitory 

 activity. This is shown in Fig. 21. It may be seen in the illustration that when 

 the inhibitory potentials set up a depolarization and when the antidromic 

 impulse is riding on top of that depolarization, an actual facilitation of axon- 



