Dissociation between scopolamine and mecamylamine during fear conditioning in rats

Abstract

State-dependent (dissociated) learning has been reported for both scopolamine (muscarinic anticholinergic) and mecamylamine (nicotinic anticholinergic). The purpose of this series of experiments was to ascertain whether dissociation would occur between these two anticholinergic compounds in a conditioned suppression task. In Experiment I, food-deprived rats were trained to drink sweetened condensed milk in a test chamber for 8 days. On Day 9, all rats received a single electric shock in the same chamber 20 min after injections of scopolamine, mecamylamine, or saline. Three days later, subgroups were tested for conditioned suppression under the same drug condition, the other drug condition, or saline. Conditioned suppression was found in all groups except those trained under scopolamine or mecamylamine and tested under saline or the other drug condition. Experiment II controlled for some of the variables which may have produced dissociation in the first experiment. The findings are interpreted to imply the existence of two separate cholinergic (nicotinic and muscarinic) pathways which mediate fear conditioning.