Ul 



JOSEF DUDEL AND STEPHEN W. KUFFLER 



Fig. 1. Intracellular records (upper sweeps) from a muscle fiber and simul- 

 taneous extracellular measurements from single junctional area (lower sweeps) 

 at stimulation rate of 1/sec. a. Excitatory stimulation alone, b. An inhibitory stimu- 

 lus is added, preceding the excitatory one by 2 msec. E.j.p.'s are reduced and 

 number of transmission failures in single junctional area (arrows) increased. The 

 diphasic portion in the intracellular records is due to a.c. amplifier. 



briefer time course than the intracellular e.j.p. (upper sweep). Out of three 

 excitatory stimuli one failed to release a quantum, while the smaller e.j.p. 

 was composed of two quanta. The arrow marks the arrival of the excitatory 

 nerve impulse near the junctions. In Fig. 2b an inhibitory stimulus was applied 

 2 msec before the excitatory stimulus (note two extracellularly recorded 

 impulses at arrows). At the single junction under the electrode, transmission 

 failure occurred twice, whereas the third time only one quantum of trans- 

 mitter was released. It was found by statistical analysis that inhibition did not 

 change the size of the quantum but only decreased the number of quanta 

 contained in the e.j.p.'s. Consequently this type of inhibition acts pre- 

 synaptically, reducing the probability of release of transmitter quanta from 

 the excitatory nerve endings. 



Applied y-aminobutyric acid (GABA) imitated in all known respects the 

 action of the inhibitory transmitter in crayfish muscle. It was shown that 

 GABA has an inhibitory effect in addition to its postsynaptic inhibitory 

 conductance increase. This and a miniinal synaptic delay of 1 msec suggest 

 chemical transmission from the inhibitory to the excitatory nerve terminals 

 in presynaptic inhibition. For details of this work three recent papers should 

 be consulted (Dudel and Kuffler, 1961a, b, c). 



