RETICULAR FACILITATION OF CAT VISUAL CORTICAL RESPONSES IS MEDIATED BY NICOTINIC AND MUSCARINIC CHOLINERGIC MECHANISMS

Stimulation of the mesencephalic reticular formation facilitates respo nses in the visual cortex elicited from the optic radiation. Using int raveneous administration of cholinergic antagonists we investigated in adult cats and two kittens whether this effect is mediated by choline rgic mechanisms. When administered alone the muscarinic antagonists at ropine and scopolamine and the nicotinic antagonist mecamylamine faile d to block reticular facilitation and sometimes even enhanced the effe cts of reticular stimulation. However, when administered in combinatio n muscarinic and nicotinic antagonists eliminated or significantly red uced the facilitation. This was even true when the two antagonists wer e administered with a time lag of several hours. These results support the notion that reticular facilitation of cortical responses is media ted by cholinergic mechanisms and suggest that this effect is mediated either by a receptor with a mixed pharmacological property or by two independent pathways acting via nicotinic and muscarinic receptors. Th is hypothesis is discussed in the context of recent evidence on cholin ergic transmission and earlier data on the pharmacology of reticular a rousal.