Cyclic AMP tastes aversive, not sweet, to rats

Electrophysiological and biochemical evidence suggests that cAMP mediates sweet taste transduction. Neural recordings from anesthetized rats and in vitro preparations demonstrate that membrane-per-meable cAMP analogues mimic the effects of sucrose and artificial sweetners. We presented solutions of sodium 8-(4-chlorophenylthio)-adenosine 3'-5'-cyclic monophosphate (8cpt-cAMP), a water-soluble, membrane-permeable cAMP analogue to freely behaving rats in short-term lickometer tests. Rats licked significantly less to 8cpt-cAMP than to sucrose or palatable saccharin solutions. Rats could taste 8cpt-cAMP solutions, however, because they licked less to 8cpt-cAMP in mixture with sucrose than to sucrose alone. Because 8cpt-cAMP decreased licking when mixed with sucrose, we conclude that the taste of 8cpt-cAMP is aversive, not sweet, to freely behaving rats.