NEUROMUSCULAR SYNAPTIC ACTIVITY IN THE CRAB 



a b c 



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Fig. 1. Cancer magistei\ intracelluiar records from closer muscle of walking leg. 

 (a), (b) and (c) are sequences obtained from three different fibers. The top 

 records in (1) show the excitatory junctional potentials recorded during stimula- 

 tion of slow motor axon at normal resting potential, the middle record represents 

 the potential change induced by a hyperpolarizing pulse (monitored in bottom 

 record). In (2) the junction potentials are recorded during application of the 

 hyperpolarizing pulse. Note the minimal enhancement (monitored in the lower 

 records). The records in (3) were obtained as in (2), but the muscle was treated 

 with GABA (10 •^g'ml). Note the complete absence of excitatory junction 

 potentials and the slight decrease in membrane resistance. 



Fig. 2. Cancer magister, closer muscle of walking leg. Effect of stimulation of the 

 inhibitory axon with 120 pulses/sec on excitatory junction potentials (fast system) 

 and membrane potential (first line) and on tension development (second line). 

 The electrical record shows slight hyperpolarization during inhibition (horizontal 

 bar) without attenuation of excitatory junction potentials (response to five periods 

 of 0-3 sec stimulation at 100 pulses/sec) while the mechanical record indicates 

 complete inhibition. Voltage calibration: 10 mV. 



