Melanopsin: An Invertebrate Mechanism Incorporated into Mammalian Photoreception

Photoreceptors are the first in a chain of neurons that process visual information.In the lateral eye of vertebrates, light hyperpolarises rod and cone photoreceptors that synapse onto bipolar and horizontal cells in the first synaptic layer of the retina.The sign of the signal is either conserved or inverted in bipolar cells, resulting in chromatically dependent hyperpolarising or depolarising responses to visual stimuli.Visual information is then conveyed to the second synaptic layer for encoding and transmission to the brain by the ganglion cells.Mammals rely on three ocular photoreceptors to sense light, rods, cones and ipRGCs.Rods and cones resolve a visual scene that allows us to interact in our environment in a conscious way.IpRGCs, through incorporation of an invertebrate opsin,