Abstract

High and low ethanol-drinking rodents show similar preferences for sweet solutions. Studies have suggested that sweet preference may be a reliable predictor of ethanol consumption in all rodents and, furthermore, that the sweet-ethanol relationship is mediated by a common biological mechanism. The present thesis investigated the role of taste preferences in ethanol intake in rats, to determine whether the relationship between ethanol and sweet intake was universal. Bitter and bittersweet solution intake were also compared with ethanol, based on research that rats find unflavoured ethanol to have a sweet and bitter taste. Fluid intake correlations among rat strains were examined following manipulation of the gabaergic, dopaminergic or opioidergic systems in order to reveal a common neural system mediating ethanol, sweet or bitter solution intake. Experiments 1 and 2 showed that saccharin and ethanol intake were not related in four rat strains. However, ethanol intake was related to saccharin-quinine intake in those strains. Experiment 3 demonstrated that intake of dilute quinine differentiated Fawn-Hooded, Lewis and Wistar rats in a similar manner to ethanol intake, suggesting that taste preferences for bitter solutions, and not sweet solutions, were a more reliable predictor of ethanol intake. Neither the GABA A agonist THIP, the dopamine D2/D3 antagonist raclopride nor the opioidergic antagonist naltrexone succeeded in altering ethanol, saccharin and quinine intake in a consistent manner in Experiment 4. Naltrexone was shown to have no effect on the intake of five flavoured fluids during continuous access drinking, but did attenuate all but quinine intake during limited access drinking. It was unclear whether the effects achieved during limited access were due to a change in palatability or some nonspecific drug effect (e.g., attenuation of locomotor activity). Overall, the findings from the current experiments challenged the notion that sweet solution preference is associated with ethanol intake in all rats, and that the opioid system is mediating this relationship. Results showed that while fluid intake interrelationships varied among the four strains tested, ethanol intake was most closely associated with the intake of a bitter and a sweet-bitter solution. In addition, the fluid intake relationships did not appear to be mediated by the gabaergic, dopaminergic or opioidergic systems.