In a series of experiments, the ability of selective μ- (β-funaltrexamine, β-FNA), δ- (naltrindole, nalt) and κ- (nor-binaltorphimine, nor-BNI) opioid receptor antagonists to attenuate the unconditioned and conditioned hyperactive effects of morphine was examined. For comparison, the nonselective opioid receptor antagonist naloxone (nalx) was also examined. Locomotor activity served as the behavioral measure. Experiment 1 found that doses of 1 and 4, but not 16 mg/kg, of morphine effectively produced conditioned hyperactivity (CH). Experiments 2a-d found that β-FNA, nalt, nor-BNI and nalx, respectively, attenuated unconditioned morphine-induced hyperactivity. Experiments 3a-c, however, found that none of the selective antagonists, given individually, attenuated CH. In contrast, nalx did attenuate CH (Experiment 3d). Collectively results suggest that the unconditioned and conditioned hyperactive responses to morphine are mediated by different receptor systems and that activation of multiple opioid-receptor subtypes mediate expression of CH.
|Number of pages||12|
|Journal||Pharmacology Biochemistry and Behavior|
|State||Published - 2002|
Bibliographical noteFunding Information:
The authors wish to thank B. Castle who helped conduct Experiment 2 and T. Green for his excellent technical assistance. The authors also wish to thank the National Institute on Drug Abuse (Bethesda, MD) for the supply of morphine sulfate and opioid antagonists. This research was supported by a USPHS grant DA 07746 and A.S. Rauhut was supported by a USPHS grant T32 DA07304.
- Locomotor activity
ASJC Scopus subject areas
- Clinical Biochemistry
- Biological Psychiatry
- Behavioral Neuroscience