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NEUROMUSCULAR SYNAPTIC ACTIVITY IN ' # 

 THE CRAB (CANCER MAGISTER)* 



Ernst Florey and Graham Hoyle 



Department of Zoology, University of Washington, Seattle 5, Washington, and 

 Department of Zoology, University of Glasgow, Glasgow 



INTRODUCTION 



Nervous inhibition in crustacean muscles has been divided by Marmont 

 and Wiersma (1938) into two categories, simple and supplemented, according 

 to whether or not the action potentials are attenuated. These are now moie 

 commonly referred to as /3- and a-inhibition, following the usage of Katz 

 (1949). 



The chemical nature of the transmitters involved in neuromuscular trans- 

 mission in Crustacea is still unknown. There are, however, a few substances 

 which in low concentration affect synaptic activity and membrane behaviour 

 in these animals. Some of these effects resemble those of nerve action, others 

 interfere with synaptic transmission in such a way that they too become useful 

 tools in the experimental approach to processes of excitation and inhibition. 



y-Aminobutyric acid (GABA), which occurs in vertebrate central nervous 

 system, has a powerful inhibitory action in many crustacean synapses. As an 

 active component of Factor I it was considered possible that this compound 

 represents the natural inhibitory transmitter. Edwards and Kuffler (1959) had 

 shown that GABA mimics the action of inhibitory neurons on the stretch 

 receptor cells of crayfish, and Van der Kloot and Robbins (1959) reported 

 that it, like Factor I containing extracts (Florey, 1954), inhibits neuromuscular 

 transmission in the crayfish, possibly by reducing the junctional excitatory 

 potentials. 



Picrotoxin blocks the action of inhibitory neurons on the heart-ganghon 

 and on somatic muscle in crayfish (Florey, 1957; Van der Kloot and Robbins, 

 1959). It also prevents the action of Factor I and GABA on these organs. 



Grundfest et al. (1959) found that GABA achieved its inhibitory effect on 

 lobster (Honiarus) muscle by reducing membrane resistance up to tenfold 

 which increased the membrane potential only slightly. Picrotoxin was found 

 to block the action of GABA as well as the inhibitory postsynaptic potentials. 



* This investigation was supported by grant B-1451 of the National Institutes of Health, 

 U.S. Public Health Service. It was carried out at the Friday Harbor Laboratories of the 

 University of Washington. 



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