Alteration of serotonergic innervation in the suprachiasmatic nucleus of the rat following removal of input fibers from retina and lateral geniculate nucleus.

To examine the influence of afferent input to the suprachiasmatic nucleus (SCN) on the development of serotonergic fibers in the SCN, afferent fibers from the retina and lateral geniculate nucleus (LGN) were eliminated in neonatal rats. Eight weeks after lesion, the distribution pattern of serotonergic fibers in the SCN was examined immunohistochemically. Neither bilateral enucleation nor LGN ablation altered the serotonergic fiber distribution in the SCN as compared to the normal adult rat. However, following combined lesions of bilateral enucleation and bilateral LGN ablation, the density of serotonergic fibers decreased throughout the SCN. The present results indicate that both retino-hypothalamic and geniculo-hypothalamic fibers may play an important role in the development of serotonergic innervation in the SCN in vivo.