Decreased Sensitivity to Bitter Solutions Following Chronic Opioid Receptor Blockade

Taste preferences, body weight gain, food and fluid intake in singly or group-housed rats

Two behavioral experiments were performed to determine if the housing conditions modify taste preferences, body weight gain, food and fluid intake, and alimentary diurnal pattern in adult male rats. In Experiment 1, a two-bottle 24-h preference test (salt, sweet, sour, bitter solutions versus deionized water) was performed in singly, dually or multiply housed rats. In Experiment 2, the same sapid solutions as Experiment 1 and water were contemporaneously offered to singly, dually, or multiply housed rats. Crowded rats drank more water, sweet solution, and total fluid, but less salt solution than singly or dually housed rats during dark and whole-day periods. All rats preferred sour solution, but not bitter solution, to water. In both experiments, crowded rats gained less body weight and ate less food than dually or isolated rats. These results suggest that the housing conditions influence taste preferences, food and fluid intake, body weight gain, but not alimentary diurnal pattern in rats. An important implication of these results is that in experiments in which appetite and taste are dependent variables, all rats should be housed under the same social and environmental conditions.

Pineal involvement in the alimentary behavior and taste preferences in the rat

The purpose of this experiment was to explore the effects of pinealectomy or sham pinealectomy on circadian rhythms of taste preferences, food and fluid intake and body weight gain in rats. We compared the body weight gain, the amounts of food eaten and that of deionized water, total fluid, salt, sour, sweet and bitter near-threshold solutions consumed by rats before all surgical manipulations and after pinealectomy or sham pinealectomy. The results showed that the pineal gland does not exert a major influence on circadian organization of taste preferences, drinking, feeding and body weight modifications in the rat. The failure of pinealectomy to modify light/dark rhythms of taste preferences and other related alimentary behaviors may be explained by the fact that pinealectomy does not completely eliminate circulating melatonin.