Morphine addicted and nonaddicted rats were placed on a 21-day conditioning regimen which involved the daily alternation of access to either water, sucrose-octa-acetate (SOA), or no liquid for 1 hr. The addicted rats received injections of morphine after either the SOA sessions or the no-liquid sessions. The nonaddicted rats were injected with morphine after the SOA sessions. Following the last injection the animals were given a two-bottle preference test between SOA and water. The results showed that the addicted animals that received morphine-SOA pairings had an increased preference for SOA, whereas the nonaddicted animals showed a decrease in SOA preference after the same conditioning treatments. The addicted rats that received the morphine injections on the no-liquid days showed no change in SOA preference.If a rat is allowed to consume a novel substance and is subsequently made ill, the rat will associate the flavor of the substance with the postingestional stress and avoid consuming the substance thereafter (Garcia, Ervin, & Koelling, 1967a; Revusky & Garcia, 1970). A logical counterpart to the conditioning of aversions by toxicosis would be the conditioning of increases in preference for flavors that are followed by beneficial postingestional effects. By comparison with conditioned aversions, however, the reported effects of beneficial postingestinal consequences have been small and rather difficult to obtain (Revusky & Garcia, 1970;Rozin & Kalat, 1971).Garcia, Ervin, Yorke, and Koelling (1967b) conditioned increases in preference for saccharin solutions in thiamine-deficient rats by pairing thiamine injections with the consumption of the flavored solutions. Zahorik and Maier (1969), using thiamine deficiency as the relevant need state, extended

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Rats were allowed to consume either sucrose or saline prior to being made ill by injection of either insulin or formalin, or by exposure to X-rays. A 2bottle preference test between sucrose and saline revealed that formalin was an effective agent in conditioning aversions to sucrose but not to saline. Similarly, injections of insulin were found to be effective in producing conditioned aversions to saline but not to sucrose. X irradiation produced strong aversions to either solution. The results are discussed with regard to the specific need states that insulin and formalin produce.

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Rats poisoned either immediately or 4 h after consuming one novel solution were subsequently tested with either a water vs, the conditioned novel solution choice or with a water vs. a second unconditioned novel solution choice. The results showed that: (1) there was a significant avoidance of both solutions by the immediately poisoned groups compared to their respective controls. and (2) there was a clear avoidance of the unconditioned novel solution and a marginal avoidance of the conditioned novel solution by the 4-h poisoned groups compared to their respective controls. The absence of a generalization decrement indicates that associative mechanisms such as stimulus generalization cannot adequately account for these results. An alternative explanation. based on the interaction of associative mechanisms with the habituation and sensitization of neophobia is proposed.