Morphine and ethanol pretreatment effects on expression and extinction of ethanol-induced conditioned place preference and aversion in mice.

Rationale: Opioid receptor antagonists reliably alter the expression or extinction of ethanol's conditioned motivational effects as indexed by the place conditioning procedure, suggesting endogenous opioids are normally involved. These studies examined how exogenous stimulation of opioid receptors alters ethanol's conditioned rewarding and aversive effects.

Objectives: Drugs that either directly (morphine) or indirectly (ethanol) stimulate opioid receptors were tested for their effects on the expression and extinction of ethanol-induced conditioned place preference (CPP) and conditioned place aversion (CPA).

Conditioned place aversion induced by intragastric administration of ethanol in rats.

Most experiments investigating ethanol-induced place conditioning in rats have produced conditioned place aversion (CPA). In one of the few reports of ethanol-induced conditioned place preference (CPP) in rats, selectively bred alcohol-preferring (msP) rats showed CPP in a biased procedure when ethanol was administered via intragastric (IG) catheter but not when ethanol was administered via intraperitoneal injection or by gavage. This finding suggests the importance of both route of administration and genetic variables to the outcome of place conditioning studies.

The effect of US preexposure on conditioned taste aversion: lack of postconditioning recovery of the aversion.

Although the CS preexposure effect in CTA was once viewed exclusively as an acquisition failure, recent studies have suggested that the latent inhibition phenomenon is the result of retrieval impairment. This interpretive challenge is based on the unexpected finding that recovery of the aversion occurs over a long retention interval following conditioning (Kraemer, Lariviere, & Spear, Animal Learning and Behavior, 16, 185-190, 1988; Bakner, Strohen, Nordeen, & Riccio, Physiology & Behavior, 50, 1269-1272, 1991). This study examined whether a similar recovery occurs after US preexposure.

Reinstatement of latent inhibition following a reminder treatment in a conditioned taste aversion paradigm.

Reminder treatments have been shown to facilitate the retrieval of a variety of conditioned responses. Whether or not similar results would occur with an experimental paradigm which involves primarily memory for a stimulus, i.e.

Postconditioning recovery from the latent inhibition effect in conditioned taste aversion.

Two experiments were conducted examining the effects of flavor (CS) preexposure on the retention of conditioned taste aversion. In Experiment 1, rats received preexposure to sucrose solution followed by a sucrose-illness pairing. The expected "latent inhibition" effect was obtained when testing occurred after a two-day but not an eleven-day training-to-test interval.