Direct neuronal projection from the dorsal raphe nucleus to the pineal complex of the rat: a Phaseolus vulgaris-leucoagglutinin in vivo neuronal tracing study.

By use of Phaseolus vulgaris-leucoagglutinin as an anterograde in vivo tracer, a direct projection from the dorsal raphe nucleus to the pineal complex of the rat was demonstrated. The nerve fibers extended from the dorsal raphe nucleus rostrally through the mesencephalic periaqueductal grey and entered the deep pineal from both the posterior commissure and the habenular area. A dense innervation of the deep pineal and the pineal stalk was observed, but the nerve fibers were not observed to enter the superficial pineal gland. This new neural pathway might connect the visual system with the pineal complex of the rat.