Enkephalin fibers in autonomic nuclear regions: intraspinal vs. supraspinal origin.

The present studies in the rat employ spinal transections and hemisections, dorsal and/or ventral rhizotomies to determine whether enkephalin fibers in spinal sympathetic and parasympathetic nuclei are of supraspinal, intraspinal, or peripheral origin. Our results suggest enkephalin fibers in thoracolumbar sympathetic nuclei are of both supraspinal and intraspinal origin, whereas the enkephalin innervation of the sacral parasympathetic nucleus is primarily intraspinal in origin. Furthermore, the majority of descending enkephalin systems selectivity project to the intermediolateralis, pars principalis and pars funicularis, and the dorsal commissural sympathetic nuclei, whereas intraspinal enkephalin pathways appear to exist primarily in the intercalatus spinalis and intercalatus spinalis, pars paraependymalis sympathetic nuclei. These new observations suggest that specific patterns exist for supraspinal and intraspinal enkephalin pathways.