Photosensitive ganglion cell

Photosensitive ganglion cells or (intrinsically) photosensitive ganglion cells (ipRGC) are a type of neurons in the retina of the mammalian eye, where they form a third class of photoreceptors alongside rods and cones . They belong to the retinal ganglion cells (RGC) and have only been investigated in more detail since the early 1990s. In contrast to the other ganglion cells of the retina, they are independently (intrinsically) sensitive to light (photosensitive). They contain a special photopigment, melanopsin . Melanopsin-containing ganglion cells are distributed all over the retina, but are more sensitive in the lower nasal part.

function

Photosensitive ganglion cells only make up a small proportion of the ganglion cells of the retina (around 1%). They transduce light into cellular signals much more slowly than rod or cone cells. Their function is not image or pattern recognition, but a stable perception of the ambient brightness. They fulfill at least three main functions:

• By providing information about the duration of day and night, they play an essential role in entrainment ( synchronization ) of the circadian rhythm (the clock of the body's day-night rhythm) with the 24-hour light-dark cycle. Via the retinohypothalamic tract , they send the brightness information directly to the clock generator of the circadian rhythm, the suprachiasmatic nucleus of the hypothalamus .
• Photosensitive ganglion cells are connected to other brain areas by nerves, including the area pretectalis of the epithalamus with adjacent regions of the midbrain , which mediate reflective eye movements ( colliculi superiores ) or regulate the adjustment of the pupil width to the luminance ( Edinger-Westphal-Kern ). They are therefore important for the pupillary light reflex and other reactions to changes in the light conditions in the environment.
• They are involved in the regulation and in the acute photic suppression (light-triggered suppression) of the secretion of melatonin from the pineal gland .

The photo pigment of the photosensitive ganglion cells, melanopsin, is most strongly stimulated by light in the short-wave (blue) range of the visible spectrum . The maximum sensitivity is at a wavelength of 480 nm .

discovery

In 1991 Russell G. Foster, Ignacio Provencio and colleagues discovered a photoreceptor in mouse eyes that could not be assigned to either the cone or the rod type. It has been shown that this receptor was involved in the circadian rhythm, the 24-hour rhythm of the biological clock. The fact that such an important discovery was published in a relatively little-known journal shows the skepticism that the scientific community initially felt about the existence of another type of photoreceptor. After all, the eye had been studied in depth for 200 years, so, as Foster himself wrote, it must seem unlikely that any other type of receptor could have gone unnoticed. Provencio et al. Published in 2007 that the newly discovered cells contain melanopsin.

Individual evidence

1. ^ Russell Foster: The discovery and characterization of a third class of photoreceptor in the vertebrate eye. . The Medical Sciences Division, University of Oxford. 2008. Archived from the original on August 31, 2009. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved July 31, 2011. 
2. ↑ licht.de: Effect of light on people. In: licht.wissen 19, p. 14. licht.de, March 1, 2014, accessed on October 27, 2017 . 
3. ↑ Kwoon Y. Wong, Felice A. Dunn, David M. Berson: Photoreceptor Adaptation in Intrinsically Photosensitive Retinal Ganglion Cells. In: Neuron. Vol. 48, No. 6, 22 December 2005, ISSN  0896-6273 , pp. 1001-1010, PMID 16364903 , doi: 10.1016 / j.neuron.2005.11.016
4. ↑ H. Bailes, R. Lucas: Human melanopsin forms a pigment maximally sensitive to blue light (λmax ≈ 479 nm) supporting activation of G (q / 11) and G (i / o) signaling cascades . In: Proceedings of the Royal Society B: Biological Sciences . Volume 280, No. 1759, May 2013. doi : 10.1098 / rspb.2012.2987 . PMID 23554393 . PMC 3619500 (free full text).
5. ^ RG Foster, I. Provencio, D. Hudson, S. Fiske, W. De Grip, M. Menaker: Circadian photoreception in the retinally degenerate mouse (rd / rd). In: Journal of Comparative Physiology A. Vol. 169, No. 1, July 1991, ISSN  0340-7594 , pp. 39-50, doi: 10.1007 / BF00198171 , PMID 1941717 .
6. ^ Russell G. Foster: Bright blue times. In: Nature . Vol. 433, No. 7027, February 17, 2005, pp. 698-699, doi: 10.1038 / 433698a .
7. ↑ T. Kumbalasiri, MD Rollag, MC Isoldi, AM de Lauro Castrucci, I. Provencio: Melanopsin Triggers the Release of Internal Calcium Stores in Response to Light. In: Photochemistry and Photobiology. Vol. 83, No. 2, March / April 2007, ISSN  0031-8655 , pp. 273-280, doi: 10.1562 / 2006-07-11-RA-964 .