FIGURE 4. New visual pathway from retina to the SCN.

From the following article:

Coordination of circadian timing in mammals

Steven M. Reppert and David R. Weaver

Nature 418, 935-941(29 August 2002)

doi:10.1038/nature00965

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a, A small population of widely dispersed, melanopsin-positive ganglion cells (red) form the retinohypothalamic tract that projects to the SCN. These ganglion cells (G) are directly light responsive. They also receive input from rods (R) and cones (C) through bipolar (B) and amacrine cells (A), some of which may contain crytochromes (blue). The precise anatomy of inputs to the melanopsin-positive neurons remains to be established. Glutamate (Glu) and PACAP mediate light effects on the mPer genes in SCN neurons. b, Light at night activates mPer1 expression through phosphorylated CREB, independent of CLOCK–BMAL1 E-box control. Red and green arrows indicate interacting negative and positive loops of the clockwork, respectively.

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