Section 6
Chapter 5,369

Environmental modification of tolerance to morphine discriminative stimulus properties in rats

Sannerud, C.A.; Young, A.M.

Psychopharmacology 93(1): 59-68


ISSN/ISBN: 0033-3158
PMID: 3114815
DOI: 10.1007/bf02439587
Accession: 005368991

Download citation:  

The development of tolerance of the discriminative stimulus properties of morphone was examined in rats trained to discriminate saline and 3.2 mg/kg morphine under a multiple timeout 15 min, 5 min fixed-ratio 30 schedule of food delivery. Generalization gradients were generated by administering increasing doses of morphine before successive timeout periods within the experimental session. Over the course of the study, the minimal discriminable dose (MDD) of morphine under control conditions fluctuated but did not systematically increase or decrease. Acute pretreatments of 3.2-17.8 mg/kg morphine 4-24 h before a generalization test resulted in minor changes in the MDD. To examine development of tolerance, supplemental doses of morphine (17.8 mg/kg) or saline were administered twice daily whild discrimination training was either suspended or continued. Tolerance was assessed by weekly generalization tests. Greater tolerance developed to the morphine stimulus when training was suspended than when training was continued. For both training conditions, response rates during generalization tests were markedly suppressed during supplemental morphine administration, and original generalization gradients were recaptured within 2 weeks after termination of supplemental morphine administration. Supplemental saline administration did not alter the discriminative or rate-altering effects of morphine under either training condition. Thus, the magnitude of tolerance to a morphine discriminative stimulus reflected an interaction of supplemental drug treatment with the training conditions imposed during that treatment.

Environmental modification of tolerance to morphine discriminative stimulus properties in rats

Full Text Article emailed within 0-6 h: $19.90