RETINAL INPUT TO THE SUPRACHIASMATIC NUCLEUS BEFORE AND AFTER PUBERTYIN DJUNGARIAN HAMSTERS

Retinal projections to the suprachiasmatic nucleus (SCN) mediate the e ffect of photoperiod to entrain circadian rhythms and to control repro ductive maturation in the Djungarian hamster. To determine whether the retinal innervation of the SCN had fully developed by the onset of pu berty in this hamster species, prepubertal and postpubertal hamsters r eceived an intraocular unilateral injection of horseradish peroxidase (HRP), and after 24 h, the anterograde transport of HRP to the SCN was studied. In prepubertal hamsters, the retinohypothalamic tract (RHT) was found to project to the medial and caudal SCN, principally the ven trolateral regions and, to an extent, the dorsomedial portion of the n ucleus. RHT innervation was asymmetric; the SCN contralateral to the m onocular injection received the dominant projection. A similar pattern of retinal projections was found postpubertally; however, the ipsilat eral SCN was less extensively labelled with HRP and smaller as determi ned by Nissl counterstain compared to that in prepubertal hamsters. Th ese findings indicate that modifications in the retinal innervation of the SCN occur as late as puberty, and may be part of a developmental change in the mechanism which processes photoperiodic information duri ng sexual maturation.