Correspondence of Visual Projections and Neuropeptide Y Distribution in the Suprachiasmatic Nucleus of the Golden Hamster

The suprachiasmatic nucleus (SON) in the anterior hypothalamus appears to be a circadian oscillator and is important for synchronizing circadian rhythms to the environmental light-dark cycle. The SON receives visual afferent projections from the retina via the retinohypothalmic tract (RHT), as well as from the lateral geniculate nucleus via the geniculohypothalamic tract (GHT). These two visual projections have been identified in many mammalian species. Recent evidence suggests that neuropeptide Y-containing fibers originating from the GHT modulate circadian rhythmicity. We examined the relationship between neuropeptide Y (NPY) receptor density and RHT projections to the SON in the golden hamster.