en Physiology Physiology Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine Bulbospinal noradrenergic pathways are shown to have an important role in descending inhibition of pain sensation. Locus ceruleus (LC), as a rich noradrenergic nucleus in the brain stem which has projections into the dorsal horn of the spinal cord, was evaluated for antinociceptive activity by using tonic and phasic pain models in the rat. LC-lesioned rats demonstrated moderate increase in both phases of the formalin test, but did not show any effect to thermal noxious stimuli, applied in the tail-flick test. These results indicate the relative involvement of LC in inhibition of tonic, but not phasic, pain. Locus Ceruleus, Formalin, Nociception, Tail flick, Norepinephrine, Tonic pain, Phasic pain. 31 34 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-604&slc_lang=en&sid=1 S SEMNANlAN 20031947532846006095 20031947532846006095 Yes From the Department Of Physiology, Shaheed Beheshti University of Medical Sciences, Tehran, IslamicRepublic of Iran. M DASHTI 20031947532846006096 20031947532846006096 No