Effects of (+)-pentazocine on the antinociceptive effects of (-)-pentazocine in mice

ABSTRACT Previous studies have shown that sigma‐1 receptor chaperone (Sig‐1R) ligands can regulate pain‐related behaviors, and Sig‐1R itself can regulate μ‐opioid receptor functions as well as signal transduction. Even though (±)‐pentazocine has been used clinically for the treatment of pain through opioid receptors, (+)‐pentazocine is known to be a selective Sig‐1R agonist. To the best of our knowledge, there is no information available regarding the involvement of Sig‐1R agonistic action in the antinociceptive effects of (±)‐pentazocine. Therefore, the present study was designed to investigate the effects of (+)‐pentazocine on the antinociceptive effects of (–)‐pentazocine in mice. Both and (–)‐pentazocine induced biphasic antinociceptive effects as measured by the warm‐plate test. The early phase, but not the delayed phase, of the antinociceptive effects induced by (–)‐pentazocine, which are mediated by the activation of μ‐opioid receptors, were suppressed by pretreatment with (+)‐pentazocine. These results suggest that the innate antinociceptive action of (±)‐pentazocine could be marginally reduced by the effects of (+)‐pentazocine, but (+)‐pentazocine can suppress the antinociceptive effects of (–)‐pentazocine at certain time points. Synapse 69:166–171, 2015. © 2015 Wiley Periodicals, Inc. The innate antinociceptive action of (±)‐pentazocine through µ‐opioid receptors could be marginally reduced by the effects of (+)‐pentazocine. (+)‐Pentazocine can suppress antinociceptive effects of (–)‐pentazocine at certain time point.