Diprenorphine as a stimulus in drug discrimination learning

Conditioned Taste Avoidance Drug Discrimination Procedure: Assessments and Applications

In the present chapter, we summarize much of the work on the taste avoidance drug discrimination procedure, presenting the logic for its initial introduction and the extension of the procedure in the investigation of the discriminative properties of various drugs. Results from these assessments parallel those from more traditional operant and maze designs in classifying and characterizing the discriminative properties of drug. At the same time, this design reveals a procedure that is sensitive in such assessments by indexing these stimulus properties more rapidly and at lower doses than in the more traditional procedures (in some cases for drugs heretofore resistant in their detection). Importantly, much remains to be learned about the taste avoidance procedure in that the nature of such learning remains unknown and the specific parameters under which it can be established and generalized and its neurochemical and neuroanatomical bases are largely unexplored. The application of drug discrimination learning to human drug abuse continues to be an important consideration for this specific design (as well as that of drug discrimination procedures in general), and recent parallels between drug use and food intake in terms of its regulation by interoceptive stimuli suggests a possible role of the loss of stimulus control in drug escalation and addiction (with possible therapeutic implications via the modulation of these interoceptive cues).

The effects of chronic morphine on the generalization of buprenorphine stimulus control: an assessment of kappa antagonist activity

Rats trained to discriminate the mixed mu agonist/kappa antagonist buprenorphine from its vehicle generalize buprenorphine control to morphine. Buprenorphine, however, does not generalize to MR2266. The generalization to morphine suggests that buprenorphine's mu agonist properties mediated in part its discriminative control. The failure to generalize to MR2266, a compound reported to block kappa-mediated effects, however, suggests that its kappa antagonist activity was not involved in its discriminative effects. The ability of buprenorphine's mu (but not kappa) activity to establish stimulus control may be a function of the overshadowing of the kappa properties of buprenorphine by its concurrent mu activity. To test this possibility, in the present experiment rats were chronically exposed to morphine prior to buprenorphine discrimination training. This procedure has been reported to result in tolerance to buprenorphine's mu agonist effects and a more pronounced display of its kappa antagonist properties. The rats were then tested for the generalization of buprenorphine control to morphine, MR2266, and pentobarbital. As expected, buprenorphine failed to generalize to the nonopioid pentobarbital. Although subjects were tolerant to morphine (as evidenced by reductions in morphine-induced behavioral effects and a rightward shift in the doses of morphine substituting for buprenorphine), buprenorphine still failed to generalize to MR2266. The failure of buprenorphine to generalize to MR2266 under conditions that should have allowed for the development of stimulus control by buprenorphine's kappa antagonist activity was discussed in terms of the general inability of kappa antagonist activity to support discrimination learning.

Nalorphine as a stimulus in drug discrimination learning: assessment of the role of mu- and kappa-receptor subtypes

Using the conditioned taste aversion baseline of drug discrimination learning, animals were trained to discriminate nalorphine from distilled water. In subsequent generalization tests, the mu-opiate agonist morphine substituted for the nalorphine stimulus in a dose-dependent manner, while the kappa-opiate agonist U50,488H and the mu-opiate antagonists naloxone and naltrexone failed to do so. That the mu-agonist morphine substituted for the nalorphine stimulus while a kappa-agonist and mu-antagonists failed to substitute indicate that the discriminative control that was established with nalorphine in the present study was mu-agonist receptor-mediated. The basis for this selective control by the mu-receptor subtype may be related to the relative salience of receptor activity in opiate-naive animals. The present results suggest that discriminative control by compounds with activity at multiple receptor sites is not uniformly mediated by specific activity at all of those sites. The specific site mediating discriminative control appears to be a function of the specific training drug.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.

Buprenorphine as a stimulus in drug discrimination learning: an assessment of mu and kappa receptor activity

Using the conditioned taste aversion baseline of drug discrimination learning, different groups of animals were trained to discriminate either buprenorphine or morphine from distilled water. Specifically, animals were injected with buprenorphine or morphine prior to a saccharin-LiCl pairing and the drug vehicle prior to saccharin alone. By the fifth conditioning trial, animals differentially consumed saccharin on the basis of administration of the drug or its vehicle. In subsequent generalization tests, buprenorphine stimulus control generalized completely to the mu agonist morphine in four of the five subjects tested, while morphine stimulus control completely generalized to buprenorphine in two of five subjects and partially generalized in the remaining three. Buprenorphine failed to generalize to the relatively selective kappa antagonist MR2266 and the broad-based antagonist diprenorphine. Morphine also failed to generalize to MR2266, but did generalize to diprenorphine. That morphine and buprenorphine displayed some degree of cross-generalization suggests that these compounds share some stimulus property, presumably their agonist activity at the mu receptor, and that the mu activity of these compounds was used in the establishment of the discrimination, a conclusion supported by the fact that compounds with mu antagonist activity (e.g., naloxone, MR2266) blocked both buprenorphine and morphine stimulus control. That buprenorphine failed to generalize to compounds with kappa antagonist activity suggests that animals trained to discriminate buprenorphine from its vehicle do not use the kappa antagonist activity of the drug in the establishment of the discrimination. The basis for the differential ability of various receptor subtypes to mediate the discriminative properties of compounds with mixed receptor activity was discussed.