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Muscular hyperalgesia of ureteral origin in rats
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Visceral Pain THE ROLE SENSATION
OF VARIOUS PERIPHERAL AFFERENT FIBERS IN PAIN PRODUCED BY DISTENSION OF THE VAGINAL CANAL IN State University, Tallahassee, RATS. K. J. Berkley,Dept. of Psychology,Florida FL 32306 USA.
BLUE Th-Fri Exhibit Hall
Abs No 779
AIM OF INVESTIGATION: This study investigated the role of pelvic and hypogastric nerve afferent fibers in pain sensation produced by vaginal distension in awake adult, virgin rats. METHODS: Rats were trained to make an “escape response” (moving their head forward into a small tube) to terminate an intense somatic stimulus (tail pinch). Following training, the ,probability and latencies of their escape responses to various amounts of vaginal distension were measured. Bilateral hypogastric or pelvic neurectomies were then performed and escape responses reassessed. Following this procedure, bilateral neurectomies were performed on the other nerve and escape responses reassessed once again. RESULTS: In all rats, as the amount of vaginal distension increased, the probability of escape responses increased and their latencies decreased. Bilateral pelvic neurectomies had no significant affect on these measures. Hypogastric neurectomies were also ineffective. CONCLUSION: These results suggest that pain sensation arising from vaginal distension is subserved by fibers in some nerve other than the pelvic or hypogastric. Since hypogastric nerve fibers apparently do not innervate the vaginal canal (l), this conclusion is not surprising. On the other hand, it has been shown in anesthetized rats that pelvic nerve fibers respond in a graded manner to increasing amounts of vaginal distension in the same range as the amounts used here (2). One possible explanation is that the pain sensation is subserved by fibers in the pudendal nerve, since it has recently been shown that their responses are closely linked with those of pelvic nerve fibers during va inal stimulation (3). REFE w ENCES: (1) Berkley, Robbins and Sato, J. Neurophvsiol., 1988; (2) Berkley, Hotta, Robbins and Sato, J. Neurophvsiol., in press; (3) Pacheco, Martinez-Gomez, Whipple, Beyer and Komisaruk, Brain Res., 1989. ACKNOWLEDGEMENT: This work was supported by NIH grant 1 ROl NS11892.
MUSCULAR HYPERALGESIA OF URETERAL ORIGIN IN RATS. Poster 240 L. Vecchiet, 0. Rampin* and D. Albe-Fessard, Institute of BLUE Th-Fri Medical Pathophysiology, University of Chieti, 66100 Chieti, Italy. Exhibit Hall OF INVFSI-IGAJlON, - Muscular hyperalgesia in man frequently develops Abs No 780 in the areas of referred pain from viscera. Some explanations have been suggested fo r the phenomenon but are objectively difficult to verify experimentally in humans, while investigations in animals could represent an easier approach. The aim of the study was therefore to develop animal models of muscular hyperalgesia of visceral origin. The research was carried out in rats by performing unilateral ureteral stimulation which produced painful behavior. Changes in muscular sensitivity were detected by measuring, on both sides, vocalization thresholds to electrical stimulation of the obliquus externus (the same muscle involved in man in the case of painful ureteral diseases). THODS: Two groups of animals were considered. In the first group, electrical stimulation was applied to one ureter to provoke vocalization and muscular thresholds were measured before the stimulation and then every 5 min afterwards for 80 min. In the second group, a stone was produced in one ureter by injecting 0.02 ml of dental cement into the upper third of the lumen under general anesthesia and daily measurements of muscular thresholds were made for 2-3 days before the operation and afterwards for 10 days. RESULT% First group: a significant w.05) decrease in threshold (hyperalgesia) occurred in the ipsilateral muscle 5 min after the end of the ureteral stimulation and lasted 30 miu, while no changes were recorded on the contralateral muscle. Repeated sessions of ureteral stimulation accentuated the hyperalgesic effect. Second group: a significant (p(o.03~p(o.004) threshold decrease appeared in the ipsilateral muscle the day after the operation and lasted 10 days. No changes were found in the contralateral muscle. CONCLUSION, Muscular hyperalgesia was obtained in rats with both kinds of unilateral ureteral stimulation. The phenomenon was transitory in the case of electrical stimulation and long-lasting after the production of a stone in the lumen; in both cases, however, it was localized in the ipsilateral obliquus extemus muscle, a result comparable to what is observed in unilateral painful ureteral diseases in man M.k
Visceral Pain THE ROLE SENSATION
OF VARIOUS PERIPHERAL AFFERENT FIBERS IN PAIN PRODUCED BY DISTENSION OF THE VAGINAL CANAL IN State University, Tallahassee, RATS. K. J. Berkley,Dept. of Psychology,Florida FL 32306 USA.
BLUE Th-Fri Exhibit Hall
Abs No 779
AIM OF INVESTIGATION: This study investigated the role of pelvic and hypogastric nerve afferent fibers in pain sensation produced by vaginal distension in awake adult, virgin rats. METHODS: Rats were trained to make an “escape response” (moving their head forward into a small tube) to terminate an intense somatic stimulus (tail pinch). Following training, the ,probability and latencies of their escape responses to various amounts of vaginal distension were measured. Bilateral hypogastric or pelvic neurectomies were then performed and escape responses reassessed. Following this procedure, bilateral neurectomies were performed on the other nerve and escape responses reassessed once again. RESULTS: In all rats, as the amount of vaginal distension increased, the probability of escape responses increased and their latencies decreased. Bilateral pelvic neurectomies had no significant affect on these measures. Hypogastric neurectomies were also ineffective. CONCLUSION: These results suggest that pain sensation arising from vaginal distension is subserved by fibers in some nerve other than the pelvic or hypogastric. Since hypogastric nerve fibers apparently do not innervate the vaginal canal (l), this conclusion is not surprising. On the other hand, it has been shown in anesthetized rats that pelvic nerve fibers respond in a graded manner to increasing amounts of vaginal distension in the same range as the amounts used here (2). One possible explanation is that the pain sensation is subserved by fibers in the pudendal nerve, since it has recently been shown that their responses are closely linked with those of pelvic nerve fibers during va inal stimulation (3). REFE w ENCES: (1) Berkley, Robbins and Sato, J. Neurophvsiol., 1988; (2) Berkley, Hotta, Robbins and Sato, J. Neurophvsiol., in press; (3) Pacheco, Martinez-Gomez, Whipple, Beyer and Komisaruk, Brain Res., 1989. ACKNOWLEDGEMENT: This work was supported by NIH grant 1 ROl NS11892.
MUSCULAR HYPERALGESIA OF URETERAL ORIGIN IN RATS. Poster 240 L. Vecchiet, 0. Rampin* and D. Albe-Fessard, Institute of BLUE Th-Fri Medical Pathophysiology, University of Chieti, 66100 Chieti, Italy. Exhibit Hall OF INVFSI-IGAJlON, - Muscular hyperalgesia in man frequently develops Abs No 780 in the areas of referred pain from viscera. Some explanations have been suggested fo r the phenomenon but are objectively difficult to verify experimentally in humans, while investigations in animals could represent an easier approach. The aim of the study was therefore to develop animal models of muscular hyperalgesia of visceral origin. The research was carried out in rats by performing unilateral ureteral stimulation which produced painful behavior. Changes in muscular sensitivity were detected by measuring, on both sides, vocalization thresholds to electrical stimulation of the obliquus externus (the same muscle involved in man in the case of painful ureteral diseases). THODS: Two groups of animals were considered. In the first group, electrical stimulation was applied to one ureter to provoke vocalization and muscular thresholds were measured before the stimulation and then every 5 min afterwards for 80 min. In the second group, a stone was produced in one ureter by injecting 0.02 ml of dental cement into the upper third of the lumen under general anesthesia and daily measurements of muscular thresholds were made for 2-3 days before the operation and afterwards for 10 days. RESULT% First group: a significant w.05) decrease in threshold (hyperalgesia) occurred in the ipsilateral muscle 5 min after the end of the ureteral stimulation and lasted 30 miu, while no changes were recorded on the contralateral muscle. Repeated sessions of ureteral stimulation accentuated the hyperalgesic effect. Second group: a significant (p(o.03~p(o.004) threshold decrease appeared in the ipsilateral muscle the day after the operation and lasted 10 days. No changes were found in the contralateral muscle. CONCLUSION, Muscular hyperalgesia was obtained in rats with both kinds of unilateral ureteral stimulation. The phenomenon was transitory in the case of electrical stimulation and long-lasting after the production of a stone in the lumen; in both cases, however, it was localized in the ipsilateral obliquus extemus muscle, a result comparable to what is observed in unilateral painful ureteral diseases in man M.k