Prenatal development of the retinohypothalamic pathway and the suprachiasmatic nucleus in the sheep

摘要: Circadian rhythms are present during fetal life in several mammalian species. To characterize the ontogeny of neural mechanisms that account for circadian rhythmicity a precocious species, we studied prenatal development retinohypothalamic pathway lambs (gestation period 147 days), using horseradish peroxidase and wheat germ agglutinin as anterograde tracers. The suprachiasmatic nucleus was early embryonic day 52 (E52). After E58, reached its full number neurons, estimated by disector method about 160,000 cells per at E62. axons invaded from while neuroblasts were still migrating to nucleus. At E62, there strong retinal projection evolved until E121, when afferents established their definitive pattern distribution ventral central regions nucleus, adjacent hypothalamic structures. delayed week relative innervation other subcortical visual centers. findings demonstrated an pathways lambs, including pathway, suggesting entrainment may be functioning weeks before birth.