NEUROMUSCULAR SYNAPTIC ACTIVITY IN LOBSTER 



93 



THE CONDUCTILE MEMBRANE OF THE AXONS 



While the electrically excitable conductile membrane is relatively less 

 sensitive to most drugs than is synaptic membrane (Grundfest, 1957c, 1958, 

 1959) it is, nevertheless, also affected by various synaptic agents. Thus 

 D-tubocurarine, eserine and procaine, all of which inactivate the synapses of 

 eel electroplaques, also modify and eventually may block activity in the 

 electrically excitable membrane (Altamirano et ai, 1955; Grundfest, 1957b). 

 Phenethylamine (PEA), which has several actions on the lobster neuromuscular 

 junctions (Bergmann et al., 1959; Reuben et al., 1959), blocks conduction in 

 the excitatory and inhibitory axons (Fig. 1). The block is reversible. GABA 

 (y-aminobutyric acid) and picrotoxin, both of which affect profoundly the 

 activity of other sites in the system (Grundfest et al., 1959; Reuben et al., 

 1959), do not affect conduction in either axon. 



5 msec 



Fig. 1. Effects of drugs on conductile membrane of the axon. An exciter axon was 

 used in this preparation. It was stimulated in the region of the leg proximal to the 

 body with the recording electrodes placed distally. The drugs (PEA, GABA and 

 picrotoxin) were applied at a small region between the stimulating and recording 

 electrodes as a drop of a 10^^ (w/v) solution. Similar data were also obtained for 

 the inhibitory axon. a. Control spike, b. After applying PEA, conduction 

 block developed as shown by the appearance of a large electrotonic potential under 

 the delayed spike, then further delay of the latter and its disappearance, c. Block 

 of conduction shown before washing out the PEA. d. Recovery on washing. 

 Application of GABA (e) and of picrotoxin (f) did not affect the responsiveness 

 of the membrane. Addition of the fluid changed the recording conditions somewhat 

 as shown by the large stimulus artifacts and the forms of the spikes, o. After 

 reapplying PEA. h. Block nearly complete, i. Recovery on washing with Homarus 



Ringer's solution. 



