Thermal latency studies in opiate-treated mice

Background: The change in the reaction time of a tail or paw exposed to a thermal stimulus is a measure of nociceptive activity in laboratory animals. Tail-flick and plantar thermal sensitivity (Hargreaves) tests are non-invasive, minimize stress, and can be used to screen animals for phenotype and drug activity. Objective: Hargreaves testing has been widely used in rats. We investigated its use to measure the activity of opiate analgesia in mice. Methods: Mice were used in thermal stimulus studies at 1-5 hours and 1-5 days to test acute and extended release preparations of buprenorphine. Results: Hargreaves testing had limited value at 1-5 hours because mice can have an obtunded response to opiate therapy. Tail-flick studies with restrained mice are not affected by the initial locomotor stimulation. Discussion: The present report describes a simple restraint system for mice. The utility of the system is demonstrated by examining the efficacy of acute and extended release buprenorphine injections in Balb/c and Swiss mice. Conclusion: Standardized tail-flick testing provides a sensitive robust method to monitor opiate activity in mice.