Control of Acetylcholine Synthesis in Motor Nerve Terminals
This chapter is a summary of work published or in the final stages of publication done in this laboratory on the regulation of ACh synthesis in motor nerve terminals (2, 20, 21). Most of the present knowledge concerning transmitter release processes in nerve terminals is derived from electrophysiological investigations of the neuromuscular junction (11). ACh is secreted, probably by exocytosis from some protected compartment in the nerve terminals (most likely synaptic vesicles) (12, and Macintosh, this volume), in which it is stored after being locally synthesized. Choline (Ch), the substrate for ACh synthesis, is taken up from the plasma by a carrier-mediated mechanism (6). Previous investigations utilizing the rat diaphragm preparation showed that the small accumulation of Ch by nerve terminals could not be studied directly because more of the Ch was taken up by non-neural cells (3, 15). This is unfortunate because it has been shown that synaptosomes isolated from regions of the brain rich in cholinergic nerve terminals take up Ch via a sodium-dependent high affinity uptake system (SDHACU (1, 8, 10, 23). It would thus be highly advantageous to be able to study this process in a peripheral system in which physiological experiments could be carried out.
KeywordsNerve Terminal Neuromuscular Junction Cholinergic Neuron Motor Nerve Terminal Acetylcholine Synthesis
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