Papers of the Week

We previously demonstrated that in a mouse line expressing a kappa opioid receptor (KOR) mutant with all the four phosphorylation sites mutated to alanines (K4A) the selective KOR agonist U50,488H (U50)-induced anti-scratching tolerance was attenuated in males and conditioned place aversion (CPA) was reduced in females, without affecting acute U50-induced anti-scratching effect and hypo-locomotion (Huang et al, 2022, Neuropharmacology). KOR phosphorylation deficiency in K4A mice would lead to little recruitment of β-arrestin2 (arrb2) and hence greatly reduced arrb2-mediated KOR regulation, downstream signaling and behaviors. Herein we examined effects of arrb2 deletion in mice on KOR-mediated behaviors in arrb2 knockout (arrb2(-/-)) mice vs wildtype (WT) mice. We found that arrb2 deletion enhanced anti-scratching effects produced by acute U50 in males, but not in females. Intriguingly, in ovariectomized (OVX) but not sham-operated females, arrb2 deletion increased U50-induced anti-scratching effect, similar to males. Furthermore, OVX enhanced U50-induced anti-scratching effects specifically in arrb2(-/-) females, but not in WT females. Thus, ovarian hormones-related modulations may obscure the phenotype associated with arrb2(-/-) to promote the KOR-mediated anti-scratching signaling in females, while OVX unmasked it. In contrast, arrb2 deletion did not affect U50-induced CPA and had no effects on anti-scratching tolerance to repeated U50 in either male or female mice. The findings in arrb2(-/-) mice revealed both similarities and differences compared to our previous results in K4A mice. Overall, the effects of arrb2 deletion on KOR-mediated behaviors depended on specific behavioral endpoints, sex, and OVX status.