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The visual system is now known to be composed of two anatomically and functionally distinct pathways, i.e. the image-forming and non-image-forming. Photoreception of the image-forming pathway begins with rods and cones, classical photoreceptors, whereas that for the non-image-forming pathway is predominantly based on intrinsically photosensitive retinal cells containing the newly discovered photo- pigment – melanopsin. The non-image-forming visual system poorly responds to brief light stimuli, and by integrating photic energy over longer periods of time it is capable of controlling various circadian rhythms. Accumulating experimental evidence suggests that at least in mammals the non-image-forming and image-forming pathways are merged, and influence the activity of each other. In mammals, melanopsin is expressed in a small population of intrinsically photoreceptive retinal ganglion cells (ipRGCs). The ipRGCs are light responsive from birth, long before the functional development of classical photorecep- tors and the image-forming visual pathway. The photosensitivity of melanopsin relies on the presence of cis-isoforms of retinaldehyde. By analogy to invertebrate opsins, melanopsin acts as a bistable pigment, having both sensory and photoisomerase regeneration functions. The transduction pathway triggered by melanopsin results in a sustained increase in intracellular calcium. This calcium increase is mediated through a G q /G 11 – phospholipase C – IP 3 pathway, and additionally involves activation of nonselective cation channels TRPC.
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The Editorial Board
Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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