Conditioned taste aversion and cholinergic drugs: pharmacological antagonism

The effectiveness of drugs as unconditioned stimuli (UCSs) in the conditioned taste aversion (CTA) procedure may be influenced by specific pharmacological antagonism. The present studies examined the UCS effects of two carbamates, physostigmine salicylate (PS) and pyridostigmine bromide (PB), and three anticholinergic compounds, atropine methyl nitrate (AMN), atropine sulfate (AS), and benactyzine hydrochloride (BH). Individual drugs, as well as combinations of the carbamates and the anticholinergics, were studied in a two-bottle procedure in rats. The lowest effective doses for eliciting significant CTAs were PS, 0.32 mg/kg; PB, 1.00 mg/kg; AMN, 0.04 mg/kg; AS, 0.07 mg/kg and BH, 0.90 mg/kg, IP. Combinations of PS with either AMN or BH were mutually antagonistic as UCSs, whereas PS with AS was not. PB with AMN, but not with AS, also showed antagonism in the procedure. The present results suggest that the CTA procedure is well-suited for direct examination of cholinergic drug effects and may also be used to explore interactions of different classes of cholinergic drugs.