1. Solomon H. Snyder Department of Neuroscience,
2. Department of Ophthalmology, and,
3. Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
4. Present addresses: Janelia Farm Research Campus, HHMI, Ashburn, Virginia 20147, USA (H.Z.); Department of Neurobiology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115, USA (H.-W.L.).

Correspondence to: Michael Tri H. Do^1,3King-Wai Yau^1,2,3 Correspondence and requests for materials should be addressed to M.T.H.D. (Email: mdo@jhmi.edu) or K.-W.Y. (Email: kwyau@mail.jhmi.edu).

Abstract

A subset of retinal ganglion cells has recently been discovered to be intrinsically photosensitive, with melanopsin as the pigment. These cells project primarily to brain centres for non-image-forming visual functions such as the pupillary light reflex and circadian photoentrainment. How well they signal intrinsic light absorption to drive behaviour remains unclear. Here we report fundamental parameters governing their intrinsic light responses and associated spike generation. The membrane density of melanopsin is 10⁴-fold lower than that of rod and cone pigments, resulting in a very low photon catch and a phototransducing role only in relatively bright light. Nonetheless, each captured photon elicits a large and extraordinarily prolonged response, with a unique shape among known photoreceptors. Notably, like rods, these cells are capable of signalling single-photon absorption. A flash causing a few hundred isomerized melanopsin molecules in a retina is sufficient for reaching threshold for the pupillary light reflex.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.