Development and Aging of Cholinergic Synapses I. Endogenous Levels of Acetylcholine and Choline in Developing Autonomic Ganglia and Iris of the Chick (Part 1 of 2)

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Abstract
Acetylcholine (ACh) and choline (Ch) levels were measured by a sensitive micromethod in developing irises, ciliary and sympathetic ganglia of the chick, starting at 5-7 days of incubation (DI) up to 1 yr of age. The neurotransmitter is present in all 3 organs at relatively low levels (1-10 pmol) from 5 DI (iris) or 7 DI (ciliary and sympathetic ganglion). This is followed by a rapid and sustained 9-fold increase in all 3 tissues up to 14 DI. It appears that low levels of ACh may be sufficient for neurotransmission to occur in the primitive ciliary ganglion and iris. After hatching, total ACh levels continue to increase up to 1 yr of age in theh iris and ciliary ganglion and up to 3 mo. in the sympathetic ganglion. The increase may depend on either an increased functional demand for the neurotransmitter or an increased number or preganglionic terminals. In general Ch levels parallel closely the levels of ACh in each organ throughout development. ACh and Ch are present since the earliest detectable stages of development in the ganglia and iris, and their 1st increase seems to be correlated to the phase of innervation of the organs. The subsequent increase probably correlates to synaptogenesis. The close relationship between Ch and ACh levels indicates a regulatory role of Ch for ACh synthesis during neuronal development.
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