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Laser Pulse Phenomena and Applications Part 17

Tham khảo tài liệu 'laser pulse phenomena and applications part 17', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CO2 Laser Pulse-Evoked Nocifensive Behavior Mediated by C-Fibers 471 data further suggest that our laser stimuli were indeed noxious and specific to certain nocifensive behavioral elements and neuronal activity in rats. The three response components of the nocifensive behavior model were most likely mediated by C-fibers and we suggest that the present model is suitable for studying the neuronal mechanisms underlying the analgesic effects of morphine. Morphine reduces the responses of dorsal horn neurons produced by C-fibers more easily than it affects those produced by AS-fibers Jurna Heinz 1979 . This observation may explain why experimental pain in humans which is usually produced by AS-fibers is little affected by morphine Becher 1957 . Some behavioral models using phasic stimulation methods predispose human subjects and animals to respond to pain as soon as it occurs i.e. at the moment the first pain is produced by AS-fibers . The presence or absence of secondary pain will generally have no impact on the measurement. For example animals withdrew their hindpaw after high-intensity electrical stimulation Evans 1961 . This test may involve the activation of both AS- and C-fibers as well as some non-nociceptive fibers. Stimulation is stopped as soon as a response is observed. Yeomans and Proudfit 1996 suggested that most common nociceptive tests involving mechanical and thermal stimuli actually investigate only responses triggered by AS-fibers and thus are not sensitive to morphine with the exception of very high doses. In a pain-induced audible and ultrasonic vocalization experiment in rats a vocal response was clearly triggered by C-fibers and was very sensitive to morphine with an ED50 five-fold less than when it is triggered by AS-fibers Jourdan et al. 1998 . We therefore propose that our nocifensive behavioral model is suitable for studying the dynamic analgesic effects of morphine. In conclusion the present results suggest that nocifensive behavior has .