Effects of Drugs Which Depress the Peripheral Nervous System on the Reticular Activating System of the Cat

Abstract

Some drugs with depressant properties on the peripheral nervous system have been examined for depressant effects on the reticular activating system of the cat. Large doses of nicotine, or of the anti-nicotinic agents dihydro-perythroidine and mecamylamine, failed to depress the reticular activating system; non-quaternary drugs with anti-muscarinic properties, such as atropine and hyoscine, depressed it readily. Hyoscine was the most potent depressant tested and its effects could be antagonized by physostigmine. In contradistinction, depression of the reticular activating system with pentobarbitone was not antagonized by physostigmine. Lignocaine was a weak depressant of the reticular activating system, and the possibility that this might be due to a central anti-muscarinic action is discussed. Adrenergic blocking drugs, such as dihydroergotamine, phenoxybenzamine or choline 2: 6-xylyl ether, did not appear to depress the reticular activating system: the significance of this is discussed. It was concluded that the hypothetical cholinergic transmitter, acting somewhere within the reticular activating system, displayed actions analogous to the muscarinic, and not to the nicotinic, actions of acetylcholine.The discovery by Moruzzi and Magoun (1949) that electrical stimulation of the brain stem reticular formation is followed by behavioural and electroencephalographic signs of arousal in animals was an outstandingly important contribution to neurological science. The recognition of such a reticular activating system has provided neurophysiologists, and in particular Magoun and his associates, with a means of disentangling some of the complex reactions of the brain to the influx of sensory information; it has stimulated neuroanatomists in their search for recognizable functional pathways inter-connecting cortex and midbrain; and it has given neuropharmacologists a valuable tool for investigating the effects of drugs upon the elusive central synapse.The demonstration that the reticular formation is particularly susceptible to the depressant effects of hypnotic and anaesthetic agents (French, Verzeano, and Magoun, 1953a;Arduini and Arduini, 1954) has been followed by several useful analyses of the effects of various drugs on the reticular arousal system (for example, Domino,

Some Neurochemical Aspects of the Depressant Action of Γ‐butyrolactone on the Central Nervous System

“…It is tempting to link these sharply localized changes in acetylcholine level with functional changes known to be induced by drugs in this region. In this context, cholinergic mechanisms in the reticular formation have been indirectly implicated (Exley, Fleming & Espelien, 1958). Our results may provide more direct evidence for such mechanisms, if we assume that the change in acetylcholine level are localized in the core and not in the periphery of the quadrigeminal region.…”

Effects of Nicotine on the Electroencephalogram of the Rabbit*

“…Here again it can be seen that the attack starts concomitantly in all leads.HOW do the data obtained in the rabbit compare with those from other animals? Some authors (Exley et al, 1958;Dunlop et al, 1960) reported that in cats the EEG convulsive seizure appears only with very high doses (up to 50 mg/kg), while the tremors are manifested at lower doses (see Silvette et al, 1962). Since we were not able to find any reference to the effects of nicotine on the EEG of other animals, we performed some experiments using the rat and the guinea pig.…”