NUCLEUS RAPHE OBSCURUS (NRO) REGULATION OF ANORECTAL MOTILITY IN RATS

Previous research has demonstrated that anorectal contractions in the rat are modulated by activation of spinal autonomic circuits. In the p resent study, anterograde tracing of descending pathways originating f rom the caudal nucleus raphe obscurus (nRO) revealed that this nucleus projects to cells within the intermediolateral (IML) cell column of t he thoracic cord and the sacral parasympathetic nucleus (SPN). These a natomical studies suggested that the nRO may influence the regulation of spinal reflexes of the pelvic floor. In a second set of experiments , acute rat preparations were used to investigate changes in anorectal motility during electrical stimulation of the nRO. Anorectal contract ions were measured by a fluid-filled manometer. Electrical stimulation of the nRO significantly reduced spontaneous anorectal activity when compared to baseline contractions recorded for 1 min prior to stimulat ion. Stimulation sites outside the nRO did not affect anorectal contra ctions when compared to either (a) the 1-min pre-stimulation baseline for that site or (b) the 1-min stimulation period for sites within the nRO. Stimulation of caudal portions of the nRO were more likely than the rostral nRO to reduce anorectal contractions. Given that the SPN c ontains preganglionic neurons which may be involved in control of anor ectal contractions (mediated via the pelvic nerve), the studies presen ted here suggest a functional role for nRO regulation of preganglionic motoneurons innervating the distal gut of the rat. (C) 1997 Elsevier Science B.V.