Cholinergic Mechanism Involved in Function of Mesodiencephalic Activating System

Abstract

A previous investigation 1 dealt with the action of cholinergic drugs and of atropine on the electrical activity of the rabbit brain. It was found that acetylcholine (ACh) produces a transitory change of the brain electrical activity identical with the alerting reaction evoked by a peripheral stimulus or direct stimulation of the midbrain reticular substance. 2 Isofluorophate (diisopropyl fluorophosphate; DFP), a powerful anticholinesterase agent, induces a long-lasting and continuous electroencephalographic pattern of alertness. On the other hand, atropine prevents all electroencephalographic alerting reactions, no matter how elicited. The pattern of alertness is due to the setting into activity of those mesodiencephalic structures with diffuse projections over the entire cortex, such as the midbrain reticular substance of Moruzzi and Magoun 2 and the thalamic diffuse projection system of Jasper. 3 It seems that cholinergic drugs exert a primary excitation on the mesodiencephalic system, while atropine enforces a primary paralysis of the