EXAMINING THE EFFECTS OF MU OPIOID RECEPTOR AGONISTS ON PAIN - RELATED DEPRESSION OF NESTING IN MICE

Abstract

A key goal in preclinical pain research is improving the translational value of findings by modeling pain states elicited in humans. Examining the expression and treatment of pain-related disruption of behavior represents one approach to improving the alignment between preclinical pain research and clinical settings. Past studies support the ability of the intermediate efficacy opioid, morphine, to restore pain-related depression of nesting in mice. In the present study, we aimed to investigate the effects of the low efficacy opioid, buprenorphine, and the high efficacy opioid, methadone, on lactic-acid induced depression of Nestlet shredding in male and female ICR mice. At the start of test sessions, 5 × 5 cm Nestlets were weighed and suspended from the wire lid of the home cages. Under control conditions, mice removed pieces of the suspended Nestlets to build nests. The results indicated that intraperitoneal injections of 0.18% lactic acid disrupted Nestlet shredding. Unlike morphine, both buprenorphine and methadone failed to restore acid-induced depression of shredding. In the absence of acid, both buprenorphine and methadone significantly depressed shredding. Our findings highlight the need for additional testing of these drugs across different pain procedures and noxious stimulus intensities to determine whether a balance can be achieved between their rate-decreasing and antinociceptive effects.