Brain Research, 110 (1976) 91-97 91 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands EVIDENCE FOR THE LOCAL SYNTHESIS OF A TRANSMITTER EN- ZYME (GLUTAMIC ACID DECARBOXYLASE) IN CRAYFISH PERIPH- ERAL NERVE YOSEF SARNE*, BRUCE K. SCHRIER AND HAROLD GAINER Behavioral Biology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Md. 20014 (U.S.A.) (Accepted November 17th, 1975) SUMMARY The activities of three enzymes of neurotransmitter metabolism (choline acetyl- transferase, CAT; acetylcholinesterase, ACHE; and glutamic acid decarboxylase, GAD) were studied in normal, transected, and organ cultured crayfish nerves. CAT (to a lesser extent ACHE) was dramatically decreased in activity when the nerve was cut proximal to the nerve cell bodies. GAD activity was unaffected by such proce- dures. In organ cultured nerve, where both motor and sensory axons degenerated, the CAT and AChE activities were virtually absent, whereas GAD activity remained close to normal levels. Inhibition of protein synthesis in cultured nerve caused the GAD activity to decrease rapidly. In view of these data, and the well documented fact that motor axons survive axotomy whereas sensory axons do not, a hypothesis that GAD is synthesized in the peripheral nerve is presented. INTRODUCTION In the preceding paper 1~ no significant difference was found in the general protein metabolism of sensory and motor axons in crayfish peripheral nerve. How- ever, it is well known that, in decapod crustaceans, the sensory axons synthesize acetylcholine as a neurotransmitter and contain choline acetyltransferase (CAT) 1,7,8, whereas the inhibitory motor axon synthesizes y-aminobutyric acid (GABA) as the neurotransmitter and contain glutamic acid decarboxylase (GAD)6,9,1L The excitatory motor axons appear to use glutamate as the neurotransmitter 10. Since GAD is found only in the inhibitory motor axons, and not in sensory axons 8, and CAT is exclusively found in the sensory axons 8, we concluded that measurements of these enzyme activities in crayfish mixed (sensory and motor) main nerves, under * Present address: Dept. of Behavioral Biology, Technion Medical School, Haifa, Israel.