FIGURE 1.

Retinal circuit diagram illustrating the revised model of circadian phototransduction. On the left side of the figure are the conventional labels for the different layers of the retina: OS, outer segment of the rod (R) and cone [L (long-wavelength sensitive), M (middle-wavelength sensitive), and S (short-wavelength sensitive)] photoreceptors; ONL, outer nuclear layer containing the cell bodies of the rod and cone photoreceptors and two types of horizontal cells (H1 and H2); OPL, outer plexiform layer containing the distal plexus of the photoreceptor (efferent, orange lines) axons and the (afferent, black lines) dendrites of the horizontal and bipolar neurons; INL, inner nuclear layer containing the cell bodies of the rod bipolar (RB) and two cone bipolar neurons, one achromatic cone bipolar (CB) and one S-cone bipolar (SB) neuron and amacrine neurons (AII, A17, A18); IPL, inner plexiform layer containing the plexus of axons and dendrites of the bipolar, amacrine, and ganglion neurons, which is divided into OFF and ON sublayers; GCL, ganglion cell layer containing the cell bodies of the conventional retinal ganglion cells (RGCs) and the intrinsically photosensitive retinal ganglion cells (ipRGCs) as well as a displaced S-cone amacrine (SCA). At the bottom of the figure are the two targets for ganglion cell axons, the RGC axons reaching the lateral geniculate nucleus (LGN) and the ipRGC axons reaching the suprachiasmatic nucleus (SCN). Also shown in the diagram are blue circles (Processes A–C) that represent important processes in the revised model. Process A represents cone inhibition of rods and thereby a reduction in shunting inhibition of the ipRGC by AII amacrine cells in process B. Process B also includes decoupling of shunting inhibition of AII amacrine cells via the A18 amacrine cells when the spectrally opponent SB signals “yellow.” Process C represents the en passant complex involving the SB, ipRGC, and A18 neurons.