Modulation of visceral nociceptive responses of rat spinal dorsal horn neurons by sympathectomy

We determined whether sympathectomy modulates visceral nociception under ph ysiological or inflammatory conditions. Recordings of sacral spinal dorsal horn neurons with sustained responses were performed in pentobarbitone-anes thetized rats. Graded colorectal distension (CRD, 20-100 mmHg) was used as a visceral nociceptive stimulus. Inflammation was induced by intracolonic i nstillation of turpentine (25%). Sympathectomy was produced by administerin g 6-hydroxydopamine. Inflammation produced an increase in the CRD-evoked re sponses. The CRD-evoked responses were attenuated following sympathectomy b oth under control and inflammatory conditions. These changes in the CRD-evo ked responses were associated with corresponding changes in spontaneous dis charge rate. The convergent input evoked by noxious pinch of the skin was n ot changed by any of the experimental conditions. The results indicate that sympathectomy attenuates visceral nociceptive responses and spontaneous ac tivity of sacral spinal cord neurons, without effect on convergent cutaneou s inputs, both under physiological and inflammatory conditions. NeuroReport 12:797-801 (C) 2001 Lippincott Williams & Wilkins.