Abstract PR321

Abstract

Background & Objectives: The spinal adrenergic transmission has been recognized to be important in the process of pain modulation. Several experimental studies have demonstrated the antinociceptive efficacy of spinal administration of the alpha 2 adrenergic receptor agonists. The contribution of spinal alpha 2 adrenergic receptor subtypes in modulating the trigeminal neuropathic pain remained unknown. Chronic constriction injury to the infraorbital nerve (ION-CCI) has proven a useful model for trigeminal neuropathic pain. The present study evaluated the possible role of spinal alpha 2A and alpha 2C adrenergic receptors in ION-CCI rat model. Materials & Methods: Male Sprague Dawley rats underwent unilateral CCI to the right ION. Two nylon (5-0) ligatures were tied around the ION. Series of von Frey filaments were used to determine pain hypersensitivity to mechanical stimulation on day 14 after surgery. A polyethylene (PE-10) catheter was implanted for upper cervical spinal injection of drugs. The rats were allowed to recover for 7 days. The time course of the antiallodynic effects and the dose-response effects of intrathecally administered an alpha 2A adrenergic receptor agonist guanfacine, an alpha 2A adrenergic receptor antagonist BRL 44408, an alpha 2C adrenergic receptor agonist nitrobiphenyline, and an alpha 2C adrenergic receptor antagonist JP 1302 were examined. The time course data for the dose-response effects were analyzed by two-way analysis of variance and Tukey-Kramer multiple-comparison test. Results: Intrathecal administration of guanfacine and nitrobiphenyline increased mechanical thresholds in a dose dependent manner (P <0.05). Intrathecal administration of BRL 44408 and JP 1302 did not alter mechanical thresholds. Conclusion: The results indicated that spinal alpha 2A and alpha 2C adrenergic receptors may play an important role in a rat model of trigeminal neuropathic pain.