Subtance P-immunoreactive innervation from the retina to the suprachiasmatic nucleus in the rat

The present study examined substance P (SP) innervation in the suprachiasmatic nucleus (SCN) of the rat. In the colchicine-untreated rat, SP-immunoreactive fibers formed a dense oval plexus in the ventral part of the SCN. After bilateral eye enucleation, there was a marked reduction in SP-immunoreactive fibers in the ventral part of the SCNs. The SP-immunoreactive neurons in the retinal ganglion cell layer were retrogradely labeled after injection of Fluoro-gold into the SCN. These findings indicate the presence of the SP innervation from the retina to the SCN in the rat. The role of SP in the retino-hypothalamic tract was discussed from the light-dark cycle.