*1.1.3 Discharge*

It is believed that more than 50% of total choline utilized in the production of acetylcholine, is derived straightforwardly from reprocessing of liberated acetylcholine, which is metabolized/hydrolyzed by cholinesterase to choline. This metabolically generated choline is likely to be swiftly absorbed before it diffuses away from the synaptic cleft. The disintegration of phosphatidyl-choline, which may be accelerated due to local production in Ach, is another source of choline. Choline produced from the two mentioned sources turned accessible to the space outside of the cell which is subsequently taken up by the nerve ending with high affinity. Due to the fact that choline is not able to cross blood brain barrier (BBB) when present in plasma, the metabolic origins of choline found to be more significant in the CNS. Accordingly, in the CNS, elevated choline absorption into the neurons of cholinergic system is not maximal or is saturated, suggesting the choline availability as the rate limiting step in the production of acetylcholine.
