The representation in memory of morphine’s unconditioned motivational effects depends on the nature of the conditioned stimulus

Abstract

In conditioning paradigms, morphine has both rewarding and aversive motivational properties. The rewarding motivational property is preferentially associated with places, whereas the aversive property is preferentially associated with tastes. We used this preferential associability of stimuli in combination with a higher order conditioning procedure to ask how the motivational effects of morphine are represented in memory. First-order conditioning involved the pairing of a novel taste or distinct place with an intraperitoneal injection of morphine (15 mg/kg) in two separate groups ofrats. As expected, conditioned taste aversions developed in one group and conditioned place preferences developed in the other. Second-order conditioning involved pairing the first-order taste conditioned stimulus (eS) with a distinct place es in the absence of morphine in one group and pairing the first-order place es with a distinct taste es in the absence of morphine in the other group. Ifthe first-order taste es, for example, elicits from memory a representation of the entire motivational spectrum of morphine, then the second-order place cues might be expected to reveal conditioned place preferences on the basis of differential associability findings. However, if the first-order taste es calls up only a representation of morphine's aversive effects, then second-order conditioned place aversions would be expected. We found that the firstorder taste es produced second-order conditioned place aversions. Similarly, in the other group, the first-order place es produced second-order taste preferences. In other words, only conditioning within one motivational system was observed. We propose that the first-order stimulus conditioned to morphine represents in memory only that single motivational effect of morphine to which the first-order conditioned stimulus is preferentially associable.Opiates, along with other psychoactive drugs, have both rewarding and aversive motivational properties (Sherman,

Lesions of the lateral parabrachial nucleus block the aversive motivational effects of both morphine and morphine withdrawal but spare morphine's discrimination properties.

“…An unbiased place conditioning protocol identical to that previously described was used (Mucha ct al., 1982;van der Kooy, 1987). In brief, conditioning took place in one of two distinct environments that differed in color, smell, and texture.…”

“…Morphine typically produces preferences for environments paired with its administration (Mucha & Iversen, 1984; Mucha, van der Kooy, O'Shaughnessy, & Bucenieks, 1982; Stefurak, Martin, & van der Kooy, 1990), but pairings of morphine with a flavor result in avoidance of that flavor (Cappell & LeBlanc, 1975; Stefurak et al, 1990). Indeed, a single injection of morphine can simultaneously produce both rewarding properties that result in a conditioned preference for an environment and aversive properties that result in a conditioned avoidance of a flavor that was presented in that environment (Martin, Bechara, & van der Kooy, 1988).…”

Saccharin's rewarding, conditioned reinforcing, and memory-improving properties: Mediation by isomorphic or independent processes?

“…However, there are two reasons to question the general conclusions drawn from these previous studies. First, in several learning paradigms variations in the internal states are thought to be preferentially associated with tastes over places (Garcia & Koelling, 1966; Garcia, McGowan, Ervin, & Koelling, 1968; Stefurak & van der Kooy, 1990). Thus, descriptions of taste, but not place, conditioning with saccharin may reflect scaling problems due to paradigm differences rather than to process differences.…”

“…In this second experiment, we wanted to determine whether saccharin was also more effective as a memory improver in taste paradigm than in place paradigm. The preferential associability of similar modality stimuli certainly holds true in both simple and higher order conditioning tasks (Mackintosh, 1983; Stefurak & van der Kooy, 1990). Does the ability of saccharin to act as a memory improver also depend on the modality (place vs. taste) of the test stimuli?…”