DEVELOPMENT OF A PAIN ASSESSMENTMODEL ANDEFFETS OF ANTIDEPRESSANTS ON NOCICEPTIVEJAWOPENING REFLEX IN FREE MOVING RATS

Park, Joo Young; Lee, San Han; An, Dong Gook

Abstract

The purpose of the present was devalopment of a new pain assessment model that recorded in free moving rats to eliminte of anesthetic agents in orofacial area. Antinociceptive effects and mechanisms of tricyclic antidepressants is also investigated. Fifty-five male Wistar rats (400-500gm) were anesthetized with an intraperitoneal injection of urethane (500microgram/kg) and pentobarbital sodium ((20microgram/kg). Anesthetized rats mounted in a sterotaxic instrument and a guide cannula was implanted in the lateral ventricle. The Cordinates were 0.8mm posterior to bregma, 1.5mm lateral from midline and 0.4mm ventral from the skull. Stimulating electrodes implanted in the incisor plup and recording electrodes were inserted into the belly of digastric musle. Stimulating and recording eletodes were led subcutaneously to miniature cranial connector sealed on the top of the skullwhit acrylic resin. Jaw opening reflex (JOP) was used a pian assessment. Jaw opening reflex is elicted by noxious stimulation of the incisor and is quantified by the magnitude of electromyogram of digastric muscle(dEMG). After a 48hours recovery period from surgery. JOR was recorded in free moving rats. Electrcal shock (200 sec duration, 0.5-2mA intensity, 0.5Hz) were delivered to the dental plup. Twenty subsequent electromyograms were recorded from digastric music in free moving rats. After intraperitioneal injection of 15microgram/kg impramine or nortriptyline dEMG was suppressed to 64+/-6 or 56+/-8% of the control. Intraperitioneal injection of 30microgram/kg desipramine, impramine or nortriptyline dEMG respectively to 44+/-9, 15+/-4, or 16+/-3% of the control. After intravenous injection of 12microgram/kg desipramine, imipramine or nortriptyline, dEMG was suspressed to 73 7, 50 4, or 66 7% of the control. Intravenous injection of 18microgram/kg desipramine, imipramine or nortriptyline suppressed dEMG respectively to 57+/-6, 12+/-3 or 6+/-2% of the control. To investigate the central mechanisms of antinociception of nortriptyline, naloxne, opioid receptor antagonist, methysergide, and phentolamine inhibited suppression of dEMG by intravenous injection of 18microgram/kg notriptyline from 7+/-2 to 47+/-9, from 4+/-2 to 24+/-6, and from 4+/-1 to 51+/-7% of the control resectively. these results suggest that antidepressant agents be to modulate pain transmission in orofacial area. The analgesia produced by intraperitioneal and intraventous injection of antidepressants seems to be mediated by multipule pathways such as descending pain inhibitory system.