Behavioral Effects of Antimuscarinic and Antinicotinic Compounds in Rats.
Technical rept. Sep 71-Mar 72,
EDGEWOOD ARSENAL ABERDEEN PROVING GROUND MD
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Comparisons were made between the effects of scopolamine and mecamylamine in two behavioral paradigms that have been found to be sensitive to cholinergic disruption by antimuscarinic compounds i.e., habituation and fear conditioning. In the habituation paradigm, water-deprived rats were exposed to a novel environmental chamber under either scopolamine, methscopolamine, mecamylamine, hexamethonium, or saline. Three days later all animals were returned to the same chamber which now contained a drinking tube. Time to complete 100 licks was used to assess habituation. Only the rats trained under scopolamine showed long drinking times failed to habituate to the apparatus stimuli thereby demonstrating the central muscarinic nature of the habituation process. In the fear-conditioning paradigm, hungry rats, trained to drink milk in a test chamber, received a single electric shock 20 minutes after injections of either scopolamine, mecamylamine, hexamethonium, or saline. Three days later subgroups were tested for conditioned suppression under either the same drug conditions or saline. Conditioned suppression was found in all groups except those trained under scopolamine or mecamylamine and tested under saline. Apparently the processes underlying this asymmetrical dissociation are not predominantly nicotinic or muscarinic in nature. Author