94 



HARRY GRUNDFEST AND JOHN P. REUBEN 



50m^f>C 



Fig. 2. Repetitive antidromic activity following a single orthodromic impulse in 

 an axon, after applying drugs to the presynaptic terminals. {Left) — Serotonin and 

 picrotoxin. (Upper set, on faster time base) — Control response before applying 

 drugs. Orthodromic direction indicated by initial negativity (upward) of diphasic 

 spike. After applying drugs the orthodromic spike was followed by an anti- 

 dromic response. This was the first of a burst of repetitive activity seen at half 

 speed on the time base. {Below) — Two antidromic trains on a slow time base. 

 (Right) — PEA and picrotoxin. Simultaneous recording from muscle fiber (upper 

 trace, intracellular recording) and exciter axon (lower trace). {Top) — E.p.s.p. 

 evoked by an orthodromic nerve impulse. {Middle) — The drugs diminished the 

 e.p.s.p., but caused antidromic activity which initiated further e.p.s.p.'s. The first 

 of a train of repetitive spikes and e.p.s.p.'s is seen in this record. (Bottom) — The 

 repetitive train and the summated e.p.s.p.'s are seen on a slower time base. 



THE CONDUCTILE MEMBRANE OF THE TERMINALS 



When PEA, or one of various other agents, is appHed to the neuromuscular 

 junctions themselves along with picrotoxin, a single impulse evoked by stimu- 

 lating either axon leads to a burst of antidromic repetitive impulses (Reuben etal, 

 1959). These impulses (Fig. 2), which must originate at or near the nerve 

 terminals, are propagated into the axon and are thence distributed to all the 

 muscles innervated by the fiber. These impulses also cause orthodromic 

 effects that may be recorded intracellularly in the muscle exposed to the drugs 

 (Figs. 3 and 4). PEA itself depresses the p.s.p.'s of the muscle fibers. Picrotoxin 

 suppresses the i.p.s.p.'s, while it does not affect the e.p.s.p.'s (Grundfest et al, 

 1959). The repetitive presynaptic activity caused by the combined actions of 

 the two drugs thus results in only excitatory p.s.p.'s which are now large and 

 prolonged, because of summation and facilitation of the repetitively evoked 

 responses (Fig. 3). Vertebrate presynaptic tenninals are also excited to 



