Apoptosis regulates ipRGC spacing necessary for rods and cones to drive circadian photoentrainment.

The retina consists of ordered arrays of individual types of neurons for processing vision. Here, we show that such order is necessary for intrinsically photosensitive retinal ganglion cells (ipRGCs) to function as irradiance detectors. We found that during development, ipRGCs undergo proximity-dependent Bax-mediated apoptosis. Bax mutant mice exhibit disrupted ipRGC spacing and dendritic stratification with an increase in abnormally localized synapses. ipRGCs are the sole conduit for light input to circadian photoentrainment, and either their melanopsin-based photosensitivity or ability to relay rod/cone input is sufficient for circadian photoentrainment. Remarkably, the disrupted ipRGC spacing does not affect melanopsin-based circadian photoentrainment but severely impairs rod/cone-driven photoentrainment. We demonstrate reduced rod/cone-driven cFos activation and electrophysiological responses in ipRGCs, suggesting that impaired synaptic input to ipRGCs underlies the photoentrainment deficits. Thus, for irradiance detection, developmental apoptosis is necessary for the spacing and connectivity of ipRGCs that underlie their functioning within a neural network.

Chen SK ，Chew KS ，McNeill DS ，Keeley PW ，Ecker JL ，Mao BQ ，Pahlberg J ，Kim B ，Lee SC ，Fox MA ，Guido W ，Wong KY ，Sampath AP ，Reese BE ，Kuruvilla R ，Hattar S ... -  《-》

M1 ipRGCs Influence Visual Function through Retrograde Signaling in the Retina.

Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs, with five subtypes named M1-M5) are a unique subclass of RGCs with axons that project directly to many brain nuclei involved in non-image-forming functions such as circadian photoentrainment and the pupillary light reflex. Recent evidence suggests that melanopsin-based signals also influence image-forming visual function, including light adaptation, but the mechanisms involved are unclear. Intriguingly, a small population of M1 ipRGCs have intraretinal axon collaterals that project toward the outer retina. Using genetic mouse models, we provide three lines of evidence showing that these axon collaterals make connections with upstream dopaminergic amacrine cells (DACs): (1) ipRGC signaling to DACs is blocked by tetrodotoxin both in vitro and in vivo, indicating that ipRGC-to-DAC transmission requires voltage-gated Na(+) channels; (2) this transmission is partly dependent on N-type Ca(2+) channels, which are possibly expressed in the axon collateral terminals of ipRGCs; and (3) fluorescence microscopy reveals that ipRGC axon collaterals make putative presynaptic contact with DACs. We further demonstrate that elimination of M1 ipRGCs attenuates light adaptation, as evidenced by an impaired electroretinogram b-wave from cones, whereas a dopamine receptor agonist can potentiate the cone-driven b-wave of retinas lacking M1 ipRGCs. Together, the results strongly suggest that ipRGCs transmit luminance signals retrogradely to the outer retina through the dopaminergic system and in turn influence retinal light adaptation. Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) comprise a third class of retinal photoreceptors that are known to mediate physiological responses such as circadian photoentrainment. However, investigation into whether and how ipRGCs contribute to vision has just begun. Here, we provide convergent anatomical and physiological evidence that axon collaterals of ipRGCs constitute a centrifugal pathway to DACs, conveying melanopsin-based signals from the innermost retina to the outer retina. We further demonstrate that retrograde signals likely influence visual processing because elimination of axon collateral-bearing ipRGCs impairs light adaptation by limiting dopamine-dependent facilitation of the cone pathway. Our findings strongly support the hypothesis that retrograde melanopsin-based signaling influences visual function locally within the retina, a notion that refutes the dogma that RGCs only provide physiological signals to the brain.

Prigge CL ，Yeh PT ，Liou NF ，Lee CC ，You SF ，Liu LL ，McNeill DS ，Chew KS ，Hattar S ，Chen SK ，Zhang DQ ... -  《-》

Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities.

Altimus CM ，Güler AD ，Alam NM ，Arman AC ，Prusky GT ，Sampath AP ，Hattar S ... -  《-》

M1 Intrinsically Photosensitive Retinal Ganglion Cells Integrate Rod and Melanopsin Inputs to Signal in Low Light.

Light influences various behaviors and physiological processes that occur outside of our conscious perception, including circadian photoentrainment, sleep, and even learning and mood. The M1, melanopsin-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs) relay a combination of rod/cone and melanopsin signals to drive these functions. However, little is known about how M1 ipRGCs integrate these signals in low light. We measure the dim light response of M1 ipRGCs and find that they exhibit a wide spectrum of responses to dim, scotopic light stimulation that are driven by a combination of rod pathway input and melanopsin phototransduction. The presence of rod input to M1 ipRGCs correlates with larger and more complex dendritic arbors. Collectively, these results show variability in the rod input to M1 ipRGCs and a surprising contribution of melanopsin to the light responses of M1 ipRGCs at very low light.

Lee SK ，Sonoda T ，Schmidt TM 《Cell Reports》

Melanopsin cells are the principal conduits for rod-cone input to non-image-forming vision.

Güler AD ，Ecker JL ，Lall GS ，Haq S ，Altimus CM ，Liao HW ，Barnard AR ，Cahill H ，Badea TC ，Zhao H ，Hankins MW ，Berson DM ，Lucas RJ ，Yau KW ，Hattar S ... -  《-》