Gustatory preference-aversion profiles for saccharin, quinine and alcohol in Roman high- and low-avoidance lines

Rats of the Roman high-(RHA) and low-avoidance (RLA) lines are known to differ in alcohol preference, since the RHA rats freely consume more ethanol than RLA animals. In order to investigate whether this difference in alcohol intake could be due to an alteration of the gustatory quality of ethanol induced by the selection, we compared taste preference and aversion responses of RHA and RLA rats in four procedures: saccharin-water choice; gustatory negative contrast; quinine-water choice and 10% v/v alcohol-water choice. Our results confirm that RHA rats drink more alcohol than RLA rats. In the saccharin-water choice task, RHA rats tended to show higher preference than RLA rats for the most palatable concentrations, while their aversion to the highest concentration of saccharin (50mM) was smaller than the aversion shown by RLA rats. The negative gustatory contrast test did not clearly differentiate the two lines, although only RHA rats showed significant negative contrast. Lastly, while RLA rats showed only aversion to quinine as the concentration increased, RHA rats did not show any aversion and preferred quinine to water at mid-range concentrations. To explain these results three hypotheses are briefly discussed: first, selective breeding for high avoidance learning could have enhanced brain reinforcement processes implicated in the evaluation of palatability. Secondly, selective breeding could have decreased aversiveness to quinine-adulterated solutions, as well as to saccharin and alcohol solutions which include a quinine-like taste component. Lastly, the present results suggest that the RHA rats may be high sensation-seekers whereas RLA animals are low sensation-seekers.