Physostigmine enhances performance on an odor mixture discrimination test

Acetylcholine is found within key sectors of the olfactory pathway, and is the neurotransmitter for many bulbopetal axons terminating in the glomerula r and internal plexiform layers of the olfactory bulb. The present study de termined whether systemically administered physostigmine, a cholinesterase inhibitor, alters the rat's ability to discern among odorant mixtures. Foll owing appropriate training, the performance of eight rats was measured ever y third day on an odor mixture discrimination test with six levels of diffi culty. On each test day (separated from one another by 3 days), a different drug treatment was administered [i.e., 0.00 (saline), 0.05, 0.10, or 0.20 mg/kg physostigmine]. The presentation order of the treatments was counterb alanced across subjects using 4 X 4 Latin squares. The mixture discriminati on test consisted of discerning the odor of an airstream coming from the sa turated head space of a 1% concentration of ethyl acetate from an airstream saturated with a 1% concentration of ethyl acetate and various concentrati ons of butanol (i.e., 1, 0.5, 0.1, 0.05, 0.01, or 0.005%). Physostigmine wa s found to enhance odor discrimination performance on the more difficult di scrimination tasks in a dose-related manner, suggesting that cholinergic ac tivation may sharpen the ability of rats to discern subtle differences amon g complex odor stimuli. (C) 1999 Elsevier Science Inc.