BIOCHEMICAL ORGANIZATION OF CHOLINERGIC NERVE TERMINALS IN THE CEREBRAL CORTEX

Abstract

The role of acetylcholine (ACh) as a chemical transmitter in the cerebral cortex is not as well established as it is in other parts of the central nervous system. However, all the components of the cholinergic system—ACh, choline acetyltransferase, and acetylcholinesterase—are present in cortical tissue. The identification of cholinergic pathways by the histochemical localization of acetylcholinesterase suggests that the reticular activating system terminating on cortical and striate neurons is largely cholinergic. This chapter discusses cholinergic systems in the cerebral cortex; the metabolic and membrane properties of choline transport, choline acetyltransferase, and acetylcholinesterase; the inactivation of released Ach; and compartmentation of ACh in the preterminal region. The isolation of presynaptic nerve terminals (synaptosomes) and synaptic vesicles from cerebral cortex and the study of these in vitro has suggested some organizational features of the cholinergic nerve terminal. The preterminal region has the ability to respire and produce ATP and phosphocreatine from glucose. A carrier-mediated mechanism for the transport of choline across the nerve cell membrane exists in the preterminal region. Choline acetyltransferase exists in the soluble cytoplasm of the preterminal region. Acetylcholinesterase exists on the neuronal plasma membrane facing the outside of the cell and appears to be the major agency for the inactivation of the transmitter. Acetylcholine exists in the cytoplasm and in vesicles in the preterminal region. The preterminal region has the capacity for acetylcholine synthesis. The most recently formed acetylcholine appears to be available for release on stimulation.