The recovery of acetylcholinesterase activity in the superior cervical ganglion of the rat following its inhibition by diisopropylphosphorofluoridate: A biochemical and cytochemical study

Abstract

Injection of diisopropylphosphorofluoridate into rats results in a marked inhibition of the acetylcholinesterase activity of the superior cervical ganglia and associated nerve trunks. We have followed the recovery of the activity of the enzyme in these two tissues. We have studied the recovery biochemically, analysing also the contribution of the various molecular forms of acetylcholinesterase, and cytochemically. Shortly after injection of the poison there is a rapid recovery of the acetylcholinesterase activity in the ganglia. This phase continues until about 16 h post-injection, and then it stops. The activity remains at this level for a further 80 h then there is another, but slower, accumulation of enzyme activity. Ganglia which had been decentralized prior to administration of diisopropylphosphorofluoridate show an identical pattern of recovery although the absolute amount of enzyme at each stage is lower than in normal tissues. In contrast, the acetylcholinesterase activity of the preganglionic nerve trunk does not begin to recover from the poison until at least 48 h after its injection. It reaches normal levels by 200h. Analysis of the multiple molecular forms of acetylcholinesterase show: a) that there are four major soluble forms and, chiefly, one membrane-bound form of the enzyme in the ganglion, b) there is one soluble and one membrane-bound form in the nerve trunk, c) that there is no preferential loss of any of the observed forms in response to decentralization of the ganglia and, d) that there is no preferential recovery of any form after diisopropylphosphorofluoridate poisoning. The cytochemistry reveals that the initial recovery phase is due to synthesis of the enzyme by the ganglion cells since under our incubation conditions these are the only structures which contain the enzyme for the first 48 h after injection. It is noteworthy that acetylcholinesterase activity could not be demonstrated in the synaptic region until at least 48 h after injection of the poison at which time it could also be detected in presynaptic axons; this indicates that the synaptic enzyme is derived from the preganglionic nerve. The results are discussed in terms of what proportion of normal ganglionic levels of acetylcholinesterase activity is derived from the presynaptic cholinergic nerves and how much from the postganglionic, but adrenergic, cells. It is suggested that appreciably less of the acetylcholinesterase is derived from the nerve trunk than is lost upon decentralization of the ganglia; it appears that the nerve might regulate the amount of enzyme that the postganglionic cells can synthesise and store.