Activity evoked in AMH receptors by sympathetic stimulation

ANALGESIC EFFECTS INDUCED BY SELECTIVE ACTIVATION OF THE MUSCULAR POLYMODAL RECEPTORS IN THE RAT. K. Kawakita & M. Funakoshi", Department of Oral Physiology, Gifu College of Dentistry, Hozumi, Motosu. Gifu 501-02. Janan. Aim'of Investigation: The existence of negative feed-back system in pain mechanisms has been suggested in recent studies on stress-induced analgesia and acupunrture analgesia. This study examines the nature of analgesia induced by selective activation of muscular polymodal receptors in the different bodv areas. Methods: In lightly anesthetized rats, analgesic effects induced by intra-muscular injection of chemical solutions (0.051.0 ml) were measured by modified tail flick test (TFT) and suppression rate of jaw-opening reflex (JOR) simultaneously. Test solutions used were bradykinin (100 pg/ml), KC1 (120 mM), NaCl (4.5, 9.0%) and Ringer's solution. Results: The similar dose-dependent analgesic effects were induced by intra-muscular injection of different chemicals except for Ringer's solution. The limbs were very effective sites on TFT and JOR. and facial region was effective onlv on JOR. Back and abdomen were almost &effective. In general, analgesia measured by TFT was long-lasting and naloxone reversible, and that measured by JOR was transient and less naloxone antagonized. Conclusions: The nature of analgesia induced by intramuscular iniection of chemical alrresics varied with nain measuring method. stimulus intensity and stimulating position: The polymodal recepl tors of muscles were very effective inputs for induction of analgesia. r----~-~ 1 ACTIVITYEVOKED IN AMH RECEPTORS BY SYMPATHETIC STIMULATION.1 367 Poster , W.J. Roberts and S.M. Elardo*, Neurological Sciences Inst., / Monday I Good Samaritan Hosoital and Med. Ctr.. Portland. OR 97209 ’ Adams 8 Aim of Investigation: Test for the effects of-sympatheticetterent activity on small myelinated afferent units responsive to both heat and mechanical stimuli (AMH receptors) in anesthetized cats. Methods: Adult cats were anesthetized with pentobarbital and prepared for electrophysiological recording from single afferent units in the saphenous nerve. A stimulating electrode was implanted on the lumbar sympathetic trunk to evoke activity in sympathetic efferent fibers which innervate the saphenous nerve. Afferent units were functionally identified as AMH units by conduction velocity, punctate receptive fields sensitive to touch and noxious heat, no response to cold or movement of down hairs. After characterization units were monitored for spike activity during sympathetic stimulation (SS) at 10 Hz for l-3 min. The unit's receptive field was then subjected to repeated, brief noxious heat pulses (50-54 OC, 10s duration). Responses to SS were again tested after this thermal insult. Results: Units with low mechanical thresholds ((5 gm, von Frey) were sensitized by noxious heat, but only rarely responded to SS -- never prior to sensitization. Units with high thresholds (>5 gm) were sensitized by noxious heat and gave spike responses to SS, but only after sensitization. Conclusions: Those AMH units with very low mechanical thresholds show little or no response to sympathetic stimulation whereas the high threshold units are activated by SS after sensitization by noxious heat. The latter units could mediate sympathetically evoked or exacerbated pain in skin which has been mildly damaged.