Neuromuscular synaptic activity in lobstf.r 97 



Fig. 6. Modification of spontaneous miniature potentials by NH4CI and 

 picrotoxin. Inkwriter recording. {Upper set) — a. Control, b. Ten minutes after 

 applying 40 niM NH4CI/I. c. Thirty minutes; increase in frequency and amplitude 

 is marked, d. Fifty minutes; frequency becomes low but potentials are of con- 

 siderable amplitude, e, f. Continuous recording at 90 min. Large depolarizing 

 and hyperpolarizing potentials. (Lower set) — In another experiment, picrotoxin 

 was applied and this eliminated the hyperpolarizing potentials, a. Before apply- 

 ing NH4CI. B. Thirty minutes after 40 niM NH4CI/I. was applied, c, d. Continuous 

 recording at 90 min. Depolarizing potentials were now very large, in the absence 

 of the hyperpolarizing activity. 



yet. Nevertheless, the analysis can be extended considerably, by examining 

 the miniature synaptic activities, which presumably arise from "spontaneous' 

 local activity of the presynaptic terminals (Reuben and Grundfest, 1960c). 



THE TRANSMISSIONAL MEMBRANES OF THE TERMINALS 



The inhibitory as well as excitatory synaptic membrane in lobster muscle 

 fibers produces miniature p.s.p.'s (Fig. 5). They are of considerable amplitude 

 and both types are affected by application of NH4CI (Fig. 6), an action 



