δ-Opioid receptors have been implicated in reinforcement processes and antagonists are available that produce long-lasting and selective antagonism of δ-opioid receptors in vivo. This experiment assessed the contribution of δ-opioid receptors to the antinociceptive and reinforcing properties of heroin. The effects of the irreversible δ-antagonist naltrindole-5'-isothiocyanate (5'-NTII) were evaluated on heroin self-administration and hot-plate antinociception in rats. 5'-NTII (10 nmol i.c.v.) shifted the dose-response curve for heroin self-administration downward, increasing the A50 values on the ascending and descending limbs by approximately 0.5 log units and decreasing the maximum by 33%. 5'-NTII (40 nmol i.c.v.) shifted both limbs of the heroin self-administration dose-effect curve 1.2 log units to the right and decreased the maximum by 90%. Heroin self-administration gradually returned to baseline levels over 7 or 17 days after administration of 10 or 40 nmol 5'-NTII, respectively. 5'-NTII (40 nmol i.c.v.) decreased the self-administration of 0.17 mg/infusion cocaine by 40% while having no effect on responding maintained by 0.33 or 0.67 mg/infusion. 5'-NTII attenuated the antinociceptive effects of deltorphin (δ2) in a dose-dependent manner while having no effect on antinociception elicited after i.c.v, administration of [D-Pen2,D-Pen5]-enkephalin (δ1) or [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (μ). In addition, the antinociceptive effects of heroin were not significantly affected by 5'-NTII (40 nmol i.c.v.). Therefore, 5'-NTII can attenuate the reinforcing effects of heroin at doses that do not affect its antinociceptive effects. Long-acting δ2-opioid antagonists may be beneficial in the treatment of heroin dependence or as adjuncts to reduce the abuse liability of opioid analgesics.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - 2000|
ASJC Scopus subject areas
- Molecular Medicine