ALTERATION OF SEROTONERGIC INNERVATION IN THE SUPRACHIASMATIC NUCLEUSOF THE RAT FOLLOWING REMOVAL OF INPUT FIBERS FROM RETINA AND LATERAL GENICULATE-NUCLEUS

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