Before the Rods and Cones

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Science  08 Jul 2005:
Vol. 309, Issue 5732, pp. 223
DOI: 10.1126/science.309.5732.223c

Rods and cones in the mouse retina, which are necessary for image formation, become responsive to light on the 10th day after birth (P10). The intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin and can detect brightness. By assaying the responses of retinas loaded with a fluorescent calcium indicator, Sekaran et al.examined the early postnatal development of light responses. About 5.4% of cells in the ganglion cell layer responded to 470-nm light at P4 to P5, whereas about 13.7% responded at P0 to P1. The response to light was not affected by pharmacological blockade of glutamate receptors but was absent in retinas from mice that lacked melanopsin. The fraction of light-responsive cells at birth and at P4 to P5 was greater than found in adults. The density of melanopsin-expressing cells was lower at P14 and in adults than earlier in development, peaking at about P4 to P5. ipRGCs project to the suprachiasmatic nucleus of the hypothalamus (SCN), and functional connections from ipRGCs to the SCN were present at P0. Thus, in mice, the ability to detect light substantially predates the ability to form images. — EMA

Curr. Biol. 15, 1099 (2005).

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