Sex-specific role for serotonin 5-HT2A receptor in modulation of opioid-induced antinociception and reward in mice.

Opioids are among the most effective analgesics and the mainstay of pain management. However, concerns about safety and abuse liability have challenged their widespread use by the medical community. Opioid-sparing therapies include drugs that in combination with opioids have the ability to enhance analgesia while decreasing opioid requirement as well as their side effects. Sex differences in antinociceptive responses to opioids have received increasing attention in recent years. However, the molecular mechanisms underlying sex differences related to opioid-sparing adjuncts remain largely unexplored. Using warm water tail-withdrawal as a mouse model of acute thermal nociception, our data suggest that adjunctive administration of the serotonin 5-HT 2A receptor (5-HT 2A R) antagonist volinanserin dose-dependently enhanced potency of the opioid analgesic oxycodone in male, but not female, mice. This antinociceptive-like response induced by oxycodone was also augmented in 5-HT 2A R knockout (5-HT 2A R −/− ) male, but not female mice; an effect that was reversed by Cre-loxP -mediated selective expression of 5-HT 2A R in dorsal root ganglion (DRG) neurons of 5-HT 2A R −/− littermates. Pharmacological inhibition with volinanserin or genetic deletion in 5-HT 2A R −/− animals potentiated the ability of oxycodone to reduce DRG excitability in male mice. Adjunctive volinanserin did not affect oxycodone-induced conditioned place preference (CPP), whereas it reduced oxycodone-induced locomotor sensitization in male and female mice. Together, these results suggest that adjunctive volinanserin augments opioid-induced antinociception, but not abuse-related behavior, through a sex-specific signaling crosstalk mechanism that requires 5-HT 2A R expression in mouse DRG neurons. Ultimately, our results may pave the way for the clinical evaluation of volinanserin as a potential sex-specific opioid adjuvant. [Display omitted] • Adjunctive volinanserin augments oxycodone-induced antinociception in male but not female mice. • Adjunctive volinanserin does not affect oxycodone-induced conditioned place preference in male or female mice. • Adjunctive volinanserin reduces oxycodone-induced locomotor sensitization in male and female mice. • 5-HT 2A receptor in dorsal root ganglion neurons is necessary for the adjunctive antinociceptive effect of volinanserin. • Volinanserin may serve as a new approach to augment opioid-induced analgesia. [ABSTRACT FROM AUTHOR]