Development and aging of cholinergic synapses. IV. Acetylcholinesterase and choline acetyltransferase activities in autonomic ganglia and iris of the chick.

Age-related changes in the activities of choline acetyltransferase an acetylcholinesterase in avian sympathetic ganglia, ciliary ganglia and iris have been determined throughout the posthatching life span. Kinetic characteristics of these enzymes have been analyzed in the nerve terminals in the iris from early embryonic stages to the latest periods of life. Enzyme activities and kinetics have been related to each other and also to the endogenous levels of acetylcholine. The regulation of the biosynthetic mechanism for acetylcholine through choline uptake and choline acetyltransferase activity in the developing nerve terminal have been examined. The activities of both enzymes in all tissue are reduced at later ages, which is referred to declines in Vmax, as the Km values do not vary significantly at any age. Declines with age are most pronounced in the iris, both in choline acetyltransferase activity and Vmax and in acetylcholine levels, supporting our view of the peripheral autonomic nerve terminal as a major locus for the effects of aging on the peripheral nervous system.