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Most retinal ganglion cells (RGCs) convey contrast and motion information to visual brain centers. Approximately 2% of RGCs are intrinsically photosensitive (ipRGCs), express melanopsin and are necessary for light to modulate specific physiological processes in mice. The ipRGCs directly target the suprachiasmatic nucleus (SCN) to photoentrain circadian rhythms, and the olivary pretectal nucleus (OPN) to mediate the pupillary light response. How and when this ipRGC circuitry develops is unknown.
Here, we show that some ipRGCs follow a delayed developmental time course relative to other image-forming RGCs. Specifically, ipRGC neurogenesis extends beyond that of other RGCs, and ipRGCs begin innervating the SCN at postnatal ages, unlike most RGCs, which innervate their image-forming targets embryonically. Moreover, the appearance of ipRGC axons in the OPN coincides precisely with the onset of the pupillary light response.
Some ipRGCs differ not only functionally but also developmentally from RGCs that mediate pattern-forming vision.
© 2011 McNeill et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RGC and ipRGC birthdating. (A,B) Series of representative images for birthdating of β-galactosidase-positive ipRGCs (A) and Brn3a-positive RGCs (B) at P0. Yellow arrowheads denote EdU-positive ipRGCs or Brn3a-positive RGCs, and white arrows denote EdU-negative cells. (C,D) Raw cell counts and proportions of EdU-positive ipRGCs (C) and Brn3a-positive RGCs (D). Scale bars: 50 μm.