Distinct ipRGC subpopulations mediate light’s acute and circadian effects on body temperature and sleep

Abstract

The light environment greatly impacts human alertness, mood, and cognition by acute regulation of physiology and indirect alignment of circadian rhythms. Both processes require the melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs), but the relevant downstream brain areas remain elusive. ipRGCs project widely in the brain, including to the central circadian pacemaker, the suprachiasmatic nucleus (SCN). Here we show that body temperature and sleep responses to light are absent after genetic ablation of all ipRGCs except a subpopulation that projects to the SCN. Furthermore, by chemogenetic activation of the ipRGCs that avoid the SCN, we show that these cells are sufficient for acute changes in body temperature. Our results challenge the idea that the SCN is a major relay for the acute effects of light on non-image forming behaviors and identify the sensory cells that initiate lights profound effects on body temperature and sleep.