Publisher Summary The chapter presents that the biosynthetic activities of highly differentiated cells include certain rather specific mechanisms for the elaboration of compounds peculiar to these cells in addition to more general types of reaction sequences common to all living cells. The enzyme system concerned in the production of the specific transmitter substance released by cholinergic neurons, choline acetylase, is identified in nonnervous structures like the placenta and in certain microorganisms. The production of acetylcholine depends upon phosphate-bond energy and coenzyme A. Acetylcholine is designated as a local hormone, but another secretion of nervous tissue that has much more widespread humoral actions, is vasopressin. Some measurements of the rate of incorporation of C 14 -labelled cystine into the protein of the sciatic nerve of frogs supports the concept of a centripetal migration of protein along the axon since there has been a wave of increasing protein radioactivity, which passes distally. Some measurements of the appearance of enzymic activity at different points along a degenerating nerve are also consistent with the idea that the enzyme protein is synthesized in the cell body and migrates distally, although there are indications that cholinesterase may not behave in this way.