Abstract
Purpose :
Melanopsin expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) are thought to provide the retina’s ability to measure background light intensity (irradiance). In order to explore the intraretinal influence of ipRGCs we adopted a chemogenetic approach to selectively and acutely activate ipRGCs. Using this approach we set out to determine the effect of activating ipRGCs on the retinal light response by electroretinography (ERG) and relate this to retinal cell activation by c-Fos mapping.
Methods :
Melanopsin-Cre mice were intravitreally injected with a Cre-recombinase-dependent viral vector to express engineered excitatory chemogenetic hM3Dq receptors in ipRGCs. We previously showed that using this approach and applying a drug that specifically activates hM3Dq receptors (clozapine N-oxide), we can recreate the effects of bright light to this cell class only (ipRGCs) in dark-housed mice (Milosavljevic N et al, Curr Biol, 2016). Flash ERG was performed across the 9-fold intensity range on hM3Dq mice before and after chemogenetic activation of ipRGCs. To identify cells that are excited following ipRGC activation we used c-Fos immunoreactivity as an early marker of neuronal activation.
Results :
Chemogenetic activation of ipRGCs suppressed a- and b-wave amplitudes of the scotopic ERG across the flash intensity range in hM3Dq compared to control mice. Examination of the normalized irradiance-response functions revealed a shift in b-wave but not a-wave sensitivity. No changes in a- and b-wave implicit times were detected. C-Fos mapping in the hM3Dq retinas revealed a significant number of cells that receive ipRGCs signalling. These c-Fos+ cells were localized mostly in the ganglion cell layer but some were found in the inner nuclear layer.
Conclusions :
Acute and selective activation of ipRGCs modulates the amplitude of both a- and b-waves of the scotopic ERG, indicating that the influence of this ganglion cell class on the retinal physiology extends to the photoreceptors as well as their downstream pathways. This event is associated with a significant number of excited retinal cells (c-Fos+) following ipRGCs chemogenetic activation. In sum, although rare (~5%of RGCs) ipRGCs have a wide ranging influence on retinal physiology.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.