Melanopsin is a photopigment found in specialized ganglion cells of the retina that are involved in the regulation of circadian rhythms and pupillary reflex. In structure, melanopsin is an opsin, a variety of G-protein-coupled receptor. It is presumed that melanopsin signals through a G-protein of the Gq family, as invertebrate opsins are known to do, but this is not firmly established. It is also believed to be similar to invertebrate opsins in possessing an intrinsic photoisomerase activity. Hugo is a masculine name. ... In biology and evolutionary computation, a locus is the position of a gene (or other significant sequence) on a chromosome. ... Chromosome 10 is one of the 23 pairs of chromosomes in humans. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... The Entrez Global Query Cross-Database Search System allows access to databases at the National Center for Biotechnology Information (NCBI) website. ... The National Center for Biotechnology Information (NCBI) is part of the US National Library of Medicine (NLM), which is a branch of the US National Institutes of Health. ... Swiss-Prot is a curated biological database of protein sequences created in 1986 by Amos Bairoch during his PhD and developed by the Swiss Institute of Bioinformatics and the European Bioinformatics Institute. ... The Mendelian Inheritance in Man project is a database that catalogues all the known diseases with a genetic component, and - when possible - links them to the relevant genes in the human genome. ... Photoreceptors are light-sensitive proteins involved in the function of photoreceptor cells. ... This is a dorsal root ganglion (DRG) from a chicken embryo (around stage of day 7) after incubation overnight in NGF growth medium stained with anti-neurofilament antibody. ... Human eye cross-sectional view. ... The Circadian rhythm is a name given to the internal body clock that regulates the (roughly) 24 hour cycle of biological processes in animals and plants. ... In medicine, pupil constriction (also known as the pupillary reflex) is reduction of pupil size. ... A rhodopsin molecule in the cell membrane. ... The seven transmembrane α-helix structure of a G-protein-coupled receptor. ... G-proteins, short for guanine nucleotide binding proteins, are a family of proteins involved in second messenger cascades. ...

The first electrophysiological light responses recorded from melanopsin ganglion cells were done in the lab of Dr. David Berson at Brown University. By using a combination of pharmacological agents to block synaptic communication in the retina, and isolating single melanopsin ganglion cells, his lab established melanopsin ganglion cells as being intrinsically photosensitive, and thus being a third class of mammalian photoreceptors. Further studies from his lab have concluded that melanopsin ganglion cells exhibit both light and dark adaptation, similar to classic rod and cone photoreceptors. Unlike rods and cones, however, melanopsin ganglion cells are responsible for non-image forming visual reflexes. Dr. David M. Berson Dr. David M. Berson is Professor of Medical Science at Brown University. ...

When light activates the melanopsin signaling system, the melanopsin-containing ganglion cells discharge nerve impulses, which are conducted through their axons in the optic nerve to specific brain targets. These targets include the suprachiasmatic nucleus of the hypothalamus (the master pacemaker of circadian rhythms) and the olivary pretectal nucleus (a center responsible for controlling the pupil of the eye). Melanopsin ganglion cells are thought to influence these targets by releasing from their axon terminals the neurotransmitters glutamate and pituitary adenylate cyclase activating polypeptide (PACAP). An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... The optic nerve is the nerve that transmits visual information from the retina to the brain. ... The suprachiasmatic nucleus (SCN) is a nucleus in the hypothalamus situated immediately above the optic chiasm, on either side of the third ventricle. ... In the anatomy of mammals, the hypothalamus is a region of the brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. ... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a presynaptic and a postsynaptic neuron. ... Glutamate is the anion of glutamic acid. ...

Experiments have shown that light entrainment, by which periods of behavioral activity or inactivity (sleep) are synchronized with the light-dark cycle, is not as effective in melanopsin knockout mice, while rod and cone photoreceptor double knockouts still exhibit circadian entrainment and pupillary reflex. A gene knockout is a genetically engineered organism that carries one or more genes in its chromosomes that has been made inoperative. ...

External links and references

• Illumination of the Melanopsin Signaling Pathway
• Addition of human melanopsin renders mammalian cells photoresponsive
• Induction of photosensitivity by heterologous expression of melanopsin
• Phototransduction by retinal ganglion cells that set the circadian clock
• Photoreceptor adaptation in intrinsically photosensitive retinal ganglion cells