Editing Chronobiology (section)

===Melanopsin as a circadian photopigment===
In 2002, [[Samer Hattar|Hattar]] and his colleagues showed that [[melanopsin]] plays a key role in a variety of photic responses, including [[pupillary light reflex]], and synchronization of the [[Circadian rhythm|biological clock]] to daily light-dark cycles. He also described the role of melanopsin in [[intrinsically photosensitive retinal ganglion cell|ipRGCs]]. Using a rat melanopsin gene, a melanopsin-specific antibody, and [[Immunocytochemistry|fluorescent immunocytochemistry]], the team concluded that melanopsin is expressed in some RGCs. Using a [[Beta-galactosidase]] assay, they found that these RGC [[axons]] exit the eyes together with the [[optic nerve]] and project to the [[suprachiasmatic nucleus]] (SCN), the primary circadian pacemaker in [[mammal]]s. They also demonstrated that the RGCs containing melanopsin were intrinsically photosensitive. Hattar concluded that melanopsin is the photopigment in a small subset of RGCs that contributes to the intrinsic photosensitivity of these cells and is involved in their non-image forming functions, such as photic entrainment and pupillary light reflex.<ref name="Fly in mammalian eye" />