Evidence for the local synthesis of a transmitter enzyme (glutamic acid decar☐ylase) in crayfish peripheral nerve

The activities of three enzymes of neurotransmitter metabolism (choline acetyltransferase, CAT; acetylcholinesterase, AChE; and glutamic acid decar☐ylase, 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 procedures. 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 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.