Abstract
Purpose :
We investigate the mechanism through which intrinsically photosensitive retinal ganglion cells (ipRGCs), crucial mediators of light's influence on sleep, cognition, and mood regulation, function within the non-image-forming pathways in the context of glaucoma.
Methods :
We have used two behavioral paradigms, the open-field test (OFT) and elevated plus maze (EPM), to evaluate the anxiety level in Angiopoietin1 conditional knockout mice (A1 cKO), a model of open-angle glaucoma. To examine the ipRGC circuits, we crossed Opn4Cre-ERT2/Cre-ERT2 mice (Jackson Laboratory, 035926) with R26Syp-tdT/+ mice (Jackson Laboratory, 012570) to accurately report the projections of ipRGCs in adult brain. At 3 months old, the progeny receive an i.p. injection of tamoxifen on five consecutive days to induce ipRGC-specific expression of the synaptophysin-tdTomato fusion protein. Two weeks post-injection, brains and retinas were prepared for immunohistochemistry and confocal imaging. We also injected a viral tracer into brain targets of interest to analyze target-specific ipRGC subtype projections. In addition, cholera toxin subunit B (CTB) was injected into the eye 5 days prior to sacrifice.
Results :
The long-term damage by ocular hypertension in A1 cKO mice results in a reduced duration spent "in center" during OFT and "in open arms" in the EPM when compared to WT control, indicating a trend toward anxiety-like behavior.
Sparse yet discernible tdTomato signals were detected in key regions associated with sleep promotion, including the ventrolateral preoptic nucleus, as well as mood-regulating centers such as the lateral habenula. CTB anterograde tracing and anti-PSD-95 immunostaining in these specific regions support their identity as ipRGC terminals.
Conclusions :
We observed anxiety-like behaviors in the glaucoma mouse model and characterized ipRGC projections in the adult mouse brain with genetic tools. Our findings suggest potential neuronal circuitry underlying glaucomatous insult to the non-image-forming system. Our subsequent investigations will delve into the analysis of how these target-specific ipRGCs degenerate as glaucoma progresses, and we will elucidate the impact of their loss on behaviors.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.