The cholinergic rigidity

Abstract

NUMEROUS accounts have been given on the influence on spinal reflex activity of acetylcholine and cholinesterase inhibitors under different experimental conditions and in various animal species (cf. Machne and Unna. 1963). However, when scrutinizing the early literature, it is hard to obtain satisfying informations concerning a state of rigidity produced by acetylcholine or drugs which facilitate cholinergic transmission. This is all the more astonishing because it was known long ago that cholinolytic agents, especially atropine. exert beneficial effects on the Parkinson syndrome, including rigidity. Moreover, cholinomimetic drugs have been described to intensify not only tremor, but also rigidity in Parkinson patients (Zucker, 1925; Marinesco and Bourgignon, 1927; Duvoisin, 1967). In 1966. Arvidsson et al. reported on experiments performed with physostigmine on rat spinal motoneurons. The study was prompted by the idea that an imbalance between cholinergic and monoaminergic (especially dopaminergic) activities in the brain in favor of cholinergic dominance leads to a Parkinson-like state (Barbeau, 1962). Physostigmine is a cholinesterase inhibitor which readily penetrates the blood-brain barrier. Systemic application of the drug to preparations with an intact neuraxis induced Rigidity may be demonstrated by the appearance of tonic activity in the electromyogram during sustained muscle stretch (Fig. 6).