Mice lacking the endocannabinoid-synthesizing enzyme NAPE-PLD exhibit sex-dependent dysregulations in responsiveness to oxycodone and a natural reward

Abstract

The endogenous opioid and endogenous cannabinoid (endocannabinoid) systems are highly interconnected in the context of drug reward. Bioactive lipids known as N-acylethanolamines (NAEs), and, specifically, anandamide (AEA), influence several unwanted side effects of opioids, including dependence and tolerance. AEA undergoes degradation by the enzyme fatty-acid amide hydrolase (FAAH), whereas the biosynthesis of AEA in vivo is catalyzed by the enzyme N-acyl phosphatidylethanolamine phospholipase-D (NAPE-PLD). AEA and FAAH are implicated in opioid reward, but the impact of genetic deletion of NAPE-PLD on responsiveness to opioids remains unknown. Here we explored the role of NAPE-PLD in behavioral sensitivity to the opioid analgesic oxycodone. We evaluated NAPE-PLD knockout (KO) and wild type (WT) mice of both sexes in preclinical assays that assess either opioid-induced psychomotor responses or voluntary oral consumption of oxycodone. In our studies, genetic deletion of NAPE-PLD produced a shift in sexually dimorphic responses to oxycodone. Psychomotor response to oxycodone was reduced in female NAPE-PLD KO mice but not in males. Female NAPE-PLD KO mice consumed more oral oxycodone that female WT mice, while no genotypic differences in consumption were observed in males. Oxycodone consumption also increased the number of striatal {Delta}FosB positive cells in female WT mice, but not in male WT mice or NAPE-PLD KO mice of either sex. Additionally, NAPE-PLD KO mice of both sexes consumed more sucrose than WT mice. Together, these findings suggest that NAPE-PLD may regulate responses to opioids in a sexually dimorphic manner as the impact of genetic deletion of NAPE-PLD was greater in females than males.