The relationship between choline supply and acetylcholine synthesis /

This thesis is concerned with the relationship between choline delivery and acetylcholine synthesis in the cat superior cervical ganglion. Increasing extracellular choline did not change the amount of acetylcholine either contained in or released by ganglia, except when choline levels were increased by 100-fold in plasma. In the latter case, most of the extra ACh formed was not releasable and may have accumulated as a result of decreased acetylcholine degradation rather than increased acetylcholine synthesis.Choline transport activity in stimulated ganglia can be monitored using choline analogues and this process was found to have similar, but not identical, characteristics as the high affinity choline transport described for synaptosomes. Under certain conditions, the uptake and acetylation of choline were dissociated and, therefore, choline transport alone does not determine the rate of acetylcholine synthesis. Choline transport is activated following a conditioning stimulus, and under these conditions choline uptake is closely related to acetylcholine synthesis. It is suggested that the relationship between choline uptake and acetylation changes with the functional state or history of cholinergic neurons