M. Marchi

Norepinephrine Levels in Peripheral Nerve Terminals During Development and Aging

An important parameter of neurotransmission is the level of neurotransmitter present in nerve terminals. We have studied the adrenergic nerve terminals and axons in the chick iris as described by Ehinger (1967). Previous work from this laboratory on the development and aging of the peripheral nervous system of the chicken has shown significant age-related variations in choline and acetylcholine (ACh) levels in autonomic ganglia and iris (Marchi e t al., 1979; Marchi and Giacobini, 1980) and in choline uptake (Marchi e t al., 1980) and norepinephrine (NE) uptake (Hoffman and Giacobini, in preparation) in the iris. To determine the relationship between uptake and endogenous neurotransmitter levels we have used high pressure liquid chromatography with electrochemical detection to measure N E levels directly throughout the lifespan in the chicken iris, from 7 days of incubation (d.i.) to 6 years of age. This represents the first quantitative longitudinal study of peripheral N E levels in the same preparation encompassing the life span of the animal.

Norepinephrine uptake in aging adrenergic nerve terminals

Norepinephrine (NE) uptake has been studied in the adult (3-6 months) and aging (5 yr) chick iris, in which there is a discrete population of norepinephrine containing nerve terminals. although total accumulation of 3H-NE in the iris does not change with age, there is a decline in Na+-dependence, temperature-sensitivity, ouabain-and inhibitor -sensitivity of uptake. The results indicate either a loss of active, carrier-mediated NE uptake during aging, or a change in the biochemical and pharmacological characteristics of this uptake. changes in the composition of the organ and in the sites of accumulation of NE are considered.

THE PROCESS OF AGING IN PERIPHERAL CHOLINERGIC NEURONS

Publisher Summary The ciliary ganglion-iris preparation of the chick represents a suitable organ for studying the process of aging in a homogeneous population of cholinergic nerve cells. The development of endogenous acetylcholine (ACh) and choline (Ch) levels as well as Ch uptake and the activity of cholinergic enzymes in animals up to 7 years of age have been followed. Total choline acetyltransferase (ChAc) activity reaches its peak at 1 year, decreases to 2 years, is unvaried to 5 years, and falls at 7 years. ACh and Ch levels increase in the iris up to 1 year and then decline continuously until 7 years. Acetylcholinesterase activity, which is mostly (85%) postsynaptic, does not change between 3 months and to 6 years. The process of aging on peripheral cholinergic neurons is not a generalized phenomenon involving damage to the entire neuron or cell death as previously suggested in the studies of the CNS but is specifically directed toward the neuronal periphery (terminals).