Spinal parasympathetic enkephalin fibers: patterns and projections

The immunocytochemical distribution of enkephalin (Enk) was examined in the sacral spinal cord of the rat. Enk fibers are found interspersed among preganglionic parasympathetic neurons in the sacral parasympathetic nucleus. In addition, Enk fibers parallel the localization of primary visceral afferents found in the pelvic nerve. These findings provide a morphological substrate for enkephalin interactions with parasympathetic functions and with primary visceral inputs to the sacral cord.