Endophinergic modulation of acceptability of putative reinforcers.

A series of experiments was conducted in order to gain additional insight into how endogenous opioids may modulate taste reactivity and, thus, hedonic processes. Using a wide range of saccharin concentrations ranging from mildly preferred to aversive, it was demonstrated that naloxone reduced preference for saccharin over water. This reduction was not dependent upon concentration of saccharin and resulted in a downward displacement of the preference/aversion curve. Naltrexone was shown to result in a greater decrease in intake in animals drinking a mildly aversive quinine solution, as compared to animals drinking tap water. In conclusion, endogenous opioids may serve to broaden the range of food-related stimuli which are avidly accepted, perhaps by inhibiting any aversive component associated with ingestion.