Distinct retinohypothalamic innervation patterns predict the developmental emergence of species-typical circadian phase preference in nocturnal Norway rats and diurnal nile grass rats

摘要: How does the brain develop differently to support nocturnality in some mammals, but diurnality others? To answer this question, one might look suprachiasmatic nucleus (SCN), which is entrained by light via retinohypothalamic tract (RHT). However, because SCN more active during day all mammals studied thus far, it alone cannot determine circadian phase preference. In adult Norway rats (Rattus norvegicus), are nocturnal, RHT also projects ventral subparaventricular zone (vSPVZ), an adjacent region that expresses in-phase pattern of SCN-vSPVZ neuronal activity. contrast, Nile grass (Arvicanthis niloticus), diurnal, anti-phase activity expressed. We hypothesized these species differences result part from a weak or absent RHT-to-vSPVZ projection rats. Here, using developmental comparative approach, we assessed behavior, hypothalamic activity, and anatomy. report robust retina-to-vSPVZ develops around end second postnatal week when nocturnal wakefulness emerge. rats, however, such not emergence accompanied increased diurnal wakefulness. When considered within context previously published reports on projections variety species, current findings suggest how retina connects hypothalamus differentially shapes behavior produce animals occupy opposing temporal niches.