Master of Arts (MA)
Faculty of Science
Contemporary research investigating the effects of opiate receptor agonists and antagonists indicates a role for endorphinergic mechanisms in the control of consummatory behaviours. One way in which opiates may exert an effect on feeding is by altering the hedonic properties or palatability of food and drink. Investigations of the role of palatability in the effect of opiates on feeding and drinking have primarily considered the effect of single exposures to opiates. Recognizing that chronic exposure to opiates may result in the development of tolerance to their palatability-altering properties, the taste reactivity test, a direct measure of the hedonic properties of a tastant, was used to assess the ability of morphine to modify the palatability of a bitter quinine solution across eight conditioning trials (Experiment 1). Morphine consistently reduced aversive reactions to the quinine solution across all eight conditioning trials, but tolerance did not develop to this effect. In tests for conditioned modiﬁcation of quinine palatability, administered after the third and the eighth conditioning trial, quinine elicited conditioned attenuation of aversive reactions in the Contingent, but not in the Noncontingent group. Hence, there was evidence of drug-similar conditioned responses suggesting that an association had been established between the effect of morphine on palatability, and the taste of quinine. In order to determine how rapidly this association was established, a second experiment was conducted whereby subjects received a single injection of morphine 30 min prior to a 10 min infusion of quinine. The results of this experiment indicated that a single exposure is insufﬁcient for the formation of an association between the effect of morphine on palatability, and the taste of quinine. In summary, therefore, tolerance did not develop to the ability of morphine to attenuate aversive reactions to the taste of quinine. Furthermore, quinine elicited conditioned attenuation of aversive reactions when assessed during drug-free tests, suggesting that the palatability of quinine was conditionally altered in a positive direction following its association with morphine.
Clarke, Sharon Nicola D.A., "Morphine-induced modification of quinine palatability: Effects of multiple morphine-quinine trials" (1994). Theses and Dissertations (Comprehensive). 632.