Abstract
Nociceptive signals from the lower bowels are transmitted at two different regions in the spinal cord, the dorsal horn and the area around laminae VII and X. The present study examined the descending action from the locus coeruleus/subcoeruleus (LC/SC) on the transmission of nociceptive signals from the lower bowels at these two regions. Extracellular recordings from the spinal cord were made with a carbon filament electrode. Colorectal distention (80 mmHg) was produced by inflating a balloon inside the descending colon and rectum. Electrical stimulation of the LC/SC (30, 50 and 70 μA, 100 Hz, 0.1 ms pulses) was delivered either ipsilaterally or contralaterally. In neurons at both the dorsal horn and the area around laminae VII and X, nociceptive responses to colorectal distention were inhibited by LC/SC stimulation, and the inhibitory effect increased with the increase of LC/SC stimulus intensity. Following LC/SC lesions, LC/SC stimulation did not inhibit nociceptive responses, whereas inhibitory effects were observed by stimulation of the intact LC/SC contralateral to the recording site. These results suggest that the transmission of visceral pain at both two regions of the spinal cord is under the control of the centrifugal pathways from the LC/SC. [J Physiol Sci. 2007;57 Suppl:S106]
