The direct retinal projection to VIP neuronal elements in the rat SCN.

The connection between optic nerve terminals and vasoactive intestinal peptide (VIP)-containing neurons in the rat suprachiasmatic nucleus (SCN) was investigated using double labeling immunocytochemistry. Cholera toxin B subunit (CT) was injected into the right eyeball, and coronal sections of the SCN were then processed for CT immunocytochemistry with silver-gold intensification and VIP immunocytochemistry consecutively with DAB staining alone. In the ventrolateral portion of the SCN, CT immunoreactive (CT-IR) optic nerve terminals were found to make synaptic contacts not only with VIP-like immunoreactive (VIP-LI) dendrites, but also with VIP-LI perikarya. CT-IR nerve endings were also found to make synaptic contacts with non-VIP immunoreactive neuronal dendrites.