Normal distribution and denervation changes of neurotransmitter related enzymes in cholinergic neurones

Abstract

SUMMARY1. The activities of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were assayed in adult pigeon ciliary ganglia, in the post-synaptic ciliary and choroid nerves, and in ciliary nerve iris terminals isolated from control birds and from animals from which the oculomotor nerve was previously transacted. Enzyme activity levels were also measured in the iris terminals after surgical section of the ciliary nerves. From differences in enzyme activity between control and 3-day denervated tissues, the localization of CAT and AChE in pre-and post-synaptic elements of the ganglia and at the iris neuromuscular junctions was estimated. The fate of the preganglionic nerve terminals after denervation was investigated by electron microscopic examination ofganglia after surgical section of the oculomotor nerve.2. The CAT activity in the ganglion was distributed as follows: 60 % in presynaptic elements, 31 % in cell somas, and 9 % in intraganglionic post-synaptic axons; in the iris junctions, 98 % of the activity was present in the ciliary nerve terminals. For AChE: 20 % was present in the preganglionic terminals, 69 % in ganglion cell somas and the remaining 11 % in post-ganglionic axons; at the neuromuscular iris junctions, 20 % was found in the ciliary nerve terminals and 80 % in the iris striated muscle.3. The first changes in the fine structure of the nerve terminals were observed 14 hr after surgery, and by 24 hr marked alteration of the synaptic structure were clearly recognized. No preganglionic endings were found in 3 day-old denervated ganglia.4. There was a positive correlation between CAT activity in the control iris nerve terminals and in ganglia. After denervation, when the activity of the enzyme decreased in ganglion cell somas, there was a corresponding decrease in the postsynaptic nerves. These two findings suggest that CAT slow axoplasmic transport is related to its perikarial concentration.5. There was a 60% reduction of CAT activity in the post-synaptic elements, assayed in the 10-day denervated ganglia, which was accompanied by a 30 % decrease in activity in the iris nerve terminals. Similarly, post-synaptic AChE for AChE there were smaller changes. 6. In contrast to CAT and AChE, there were no differences in ganglionic protein content, or lactate dehydrogenase (LDH), co-enzyme A (CoA) and monoamine oxidase (MAO) levels between short-term (3 days) and long-term (10 days) denervated ganglia.7. The later decrease of CAT and AChE activity in the cell somas, axons and nerve terminals after long-term preganglionic transaction suggests that the activity of these enzymes is regulated across the synapses. It is postulated that the AChE regulation is part of a general 'trophic interaction' between neurones, but that the transsynaptic modulation of CAT is specific for cholinergic cells.

The release of acetylcholine from post‐ganglionic cell bodies in response to depolarization.

“…1. 6, CAT), the enzyme catalysing the ACh synthetic reaction, is produced in the cell body and transported by slow axonal flow to the terminal region (Fonnum, Frizell & Sj6strand, 1973;Giacobini, Pilar, Suszkiw & Uchimura, 1979). The precursors of ACh are also found in the cell body.…”

In vitro techniques for the assessment of neurotoxicity.

“…The development of cholinergic enzymes, the effect of denervation, and the effects of aging on gangliahave been reported (195,196). The avian system has several advantages.…”

Development and Aging of Cholinergic Synapses

“…Studies based on denervation [15] show that AChE is distributed 20% in the pre ganglionic terminals, 69% in ciliary ganglion cell somas and the remaining 11 % in post ganglionic axons. At the neuromuscular iris junctions 20% is found in the ciliary nerve terminals and 80% in the iris striated muscle.…”

“…Both ChAc and ACh are concentrated in the neuromuscular junctions of the iris and represent reliable presynaptic markers of cho linergic innervation [15,26]. In the terminals of the iris total ACh levels and total ChAc activity show two distinct periods of changes after hatching.…”

“…The interpreta tion of these variations is more difficult in ciliary ganglia, since ChAc and ACh are pre sent both in pre-and postganglionic com ponents. Denervation experiments have shown that ACh and ChAc activity is distributed 60-70% preganglionic and 30-40% post ganglionic [15,35], respectively. These data, although derived from adult birds, indicate that most ACh and Ch present in the ciliary ganglia of the chick is related to presynaptic terminals.…”