THE EFFECT OF LOCUS CERULEUS LESIONING ON TONIC AND PHASIC PAIN

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.