Abstract

*Dr. Tomoki Nishiyama MD, PhD

ABSTRACT

Background: We compared the effects of paw incision, intrathecal single or repeat morphine administration on three different tests of hyperalgesia using a rat model to know the characteristics of these tests. Methods: Male Sprague-Dawley rats with lumbar intrathecal catheters received a 1 cm longitudinal incision through skin and fascia of the plantar aspect of the foot followed by suture. Von Frey filament withdrawal weighting, thermal withdrawal latency, and weight bearing were evaluated for postoperative 7 days. The effects of single intrathecal morphine after surgery and repeat intrathecal morphine every day on the three methods were also studied. Results: Paw incision decreased Von Frey withdrawal weighting, thermal withdrawal latency, and weight bearing only on the operated paw. In these methods, Von Frey withdrawal weighting and thermal withdrawal latency gradually returned after 2 hours, but not to the control levels on 7 days. Single intrathecal morphine recovered Von Frey withdrawal weighting and thermal withdrawal latency dose dependently, but not weight bearing. Repeated intrathecal morphine every day induced similar recovery with single intrathecal morphine in the Von Frey withdrawal weighting, and better recovery in the thermal withdrawal latency. Conclusions: To study postoperative analgesia in a rat paw incision model, weight bearing showed different results compared to Von Frey withdrawal weighting and thermal withdrawal latency. Repeated intrathecal morphine every day after surgery induced better recovery of thermal hyperalgesia but not of tactile mechanical hyperalgesia than postoperative single intrathecal morphine.