NEUROMUSCULAR SYNAPTIC ACTIVITY IN LOBSTER 103 



leads to very different results. Substances that are inert on axodendritic 

 synaptic responses act upon the membranes of the spinal neurons. Indeed, 

 the pattern of pharmacological actions of the electrophoretically applied 

 drugs is quite different. Thus, strychnine is ineffective when applied electro- 

 phoretically, but exerts its axonal effect, blockade of inhibitory synapses, 

 when injected locally with a fine pipette. 



The individual components that have now been identified in synaptic 

 transmission must also interact by pairs, and this interaction in the ortho- 

 dromic direction is the recognized normal action. Back actions are still 

 insufficiently analyzed, but the initiation of repetitive responses after a 

 single orthodromic nerve impulse emphasizes the need to consider such back 

 effects. They are probably minimal in the back action of electrically excitable 

 activity upon electrically inexcitable membrane, and would be manifested 

 most strongly by actions of the presynaptic terminals on the conductile 

 membrane of the axon. 



Such effects would lead to disorganization of the patterns of co-ordinated 

 responses since the repetitive discharges would interfere with the controlled 

 message code of the orthodromic impulses sent out by the central nervous 

 system. Under many conditions they would lead to convulsive activity. 

 An interesting possibility arises in connection with still more complicated 

 neuron organizations than that of lobster neuromuscular junctions. Suppose 

 that an agent which blocks inhibitory synapses in the cortex (like strychnine 

 or the convulsant co-amino acids) were also to cause repetitive activity in 

 the presynaptic terminals of the ramifying nerve fibers. Various types of 

 avalanching convulsive activity would then develop. 



REFERENCES 



Altamirano, M., Coates, C. W., and Grundfest, H. (1955) Mechanisms of direct and 

 neural excitability in electroplaques of electric eel. J. Gen. Physiol. 38 : 319-360. 



Bergmann, F., Reuben, J. P. and Grundfest, H. (1959) Actions of biogenic amines and 

 derivatives on lobster neuromuscular transmission. Biol. Bull. 117 : 405. 



BoiSTEL, J. and Fatt, P. (1958) Membrane permeability change during inhibitory trans- 

 mitter action in crustacean muscle. J. Physiol. (London) 144 : 176 191. 



Curtis, D. R. (1961) The assessment of the mode of action of neurone depressants. This 

 volume, p. 342. 



Florey, E. and Hoyle, G. (1961) Neuromuscular synaptic activity in crabs. This volume, 

 p. 105. 



Furukawa, T., Furukawa, A. and Takagi, T. (1957) Fibrillation of muscle fibers pro- 

 duced by ammonium ions and its relation to the spontaneous activity at the neuro- 

 muscular junction. Japan. J. Physiol. 7 : 252-263. 



Grundfest, H. (1957a) Electrical inexcitability of synapses and some of its consequences 

 in the central nervous system. Physiol. Revs. 37 : 337-361. 



Grundfest, H. (1957b) The mechanisms of discharge of the electric organ in relation to 

 general and comparative electrophysiology. Progr. in Biophys. and Biophys. Chem. 

 7 : 1. 



