Changes In Cholinergic Activity and Avoidance Behavior By Nicotine In Differentially Housed Mice

Abstract

Mice housed either in isolation or in groups of 5 for 165 days were treated acutely with either nicotine sulfate (1.0 mg/kg) or saline prior to being trained to acquire a passive avoidance response. Isolated mice showed markedly reduced passive avoidance learning, but with nicotine treatment their avoidance acquisition was comparable with that of group-housed animals. In the case of the latter, nicotine did not affect avoidance acquisition rate. Active avoidance training, given following passive avoidance testing, indicated significantly impaired learning of the avoidance among isolated mice, without any effect upon escape from footshock. Nicotine treated isolated animals showed a significantly greater incidence of active avoidance behavior, but group-housed, nicotine-treated mice showed appreciably reduced active avoidance responding. Parallel studies of acetylcholine pools in the cerebral cortex of differentially housed, drug-treated mice indicated that isolation led to a significant decrease in the ratio of ‘bound’:‘free’ acetylcholine; nicotine treatment led to an elevation of this ratio among isolated mice, but group-housed animals given nicotine showed a significantly decreased ratio. The interaction of differential housing with drug treatment may serve as a model from which cholinergic mechanisms related to avoidance behavior may be viewed.