Melanopsin retinal ganglion cells are not labeled in Thy-1YFP-16 transgenic mice

Optimizing retinal ganglion cell nuclear staining for automated cell counting

The retinal ganglion cells (RGCs) serve as the critical pathway for transmitting visual information from the retina to the brain, yet they can be dramatically impacted by diseases such as glaucoma. When investigating disease processes affecting RGCs in mouse models, accurately quantifying affected cells becomes essential. However, the use of pan RGC markers like RBPMS or THY1 presents challenges in accurate total cell counting. While Brn3a serves as a reliable RGC nuclear marker for automated counting, it fails to encompass all RGC subtypes in mice. To address this limitation and enable precise automated counting, our research endeavors to develop a method for labeling nuclei in all RGC subtypes. Investigating RGC subtypes labeled with the nuclear marker POU6F2 revealed that numerous RGCs unlabeled by Brn3a were, in fact, labeled with POU6F2. We hypothesize that using antibodies against both Brn3a and POU6F2 would label virtually all RGC nuclei in the mouse retina. Our experiments confirmed that staining retinas with both markers resulted in the labeling of all RGCs. Additionally, when using the cell body marker RBPMS known to label all mouse RGCs, all RBPMS-labeled cells also exhibited Brn3a or POU6F2 labeling. This combination of Brn3a and POU6F2 antibodies provides a pan-RGC nuclear stain, facilitating accurate automated counting by labeling cell nuclei in the retina.

Pan-retinal ganglion cell markers in mice, rats, and rhesus macaques

Univocal identification of retinal ganglion cells (RGCs) is an essential prerequisite for studying their degeneration and neuroprotection. Before the advent of phenotypic markers, RGCs were normally identified using retrograde tracing of retinorecipient areas. This is an invasive technique, and its use is precluded in higher mammals such as monkeys. In the past decade, several RGC markers have been described. Here, we reviewed and analyzed the specificity of nine markers used to identify all or most RGCs, i.e., pan-RGC markers, in rats, mice, and macaques. The best markers in the three species in terms of specificity, proportion of RGCs labeled, and indicators of viability were BRN3A, expressed by vision-forming RGCs, and RBPMS, expressed by vision- and non-vision-forming RGCs. NEUN, often used to identify RGCs, was expressed by non-RGCs in the ganglion cell layer, and therefore was not RGC-specific. γ-SYN, TUJ1, and NF-L labeled the RGC axons, which impaired the detection of their somas in the central retina but would be good for studying RGC morphology. In rats, TUJ1 and NF-L were also expressed by non-RGCs. BM88, ERRβ, and PGP9.5 are rarely used as markers, but they identified most RGCs in the rats and macaques and ERRβ in mice. However, PGP9.5 was also expressed by non-RGCs in rats and macaques and BM88 and ERRβ were not suitable markers of viability.

Adenosine receptor expression in the adult zebrafish retina

Adenosine is an endogenous nucleoside in the central nervous system that acts on adenosine receptors. These are G protein-coupled receptors that have four known subtypes: A1, A2A, A2B, and A3 receptors. In the present study, we aimed to map the location of the adenosine receptor subtypes in adult wild-type zebrafish retina using in situ hybridization and immunohistochemistry. A1R, A2AR, and A2BR mRNA were detected in the ganglion cell layer (GCL), the inner nuclear layer (INL), the outer nuclear layer (ONL), and the outer segment (OS). A3R mRNA was detected in the GCL, ONL, and OS. A1R-immunoreactivity was expressed as puncta in the INL and in the outer plexiform layer (OPL). A1Rs were located within the cone pedicle and contiguous to horizontal cell tips in the OPL. A2AR-immunoreactivity was expressed as puncta in the GCL, inner plexiform layer (IPL), INL, and outer retina. A2AR puncta in the outer retina were situated around the ellipsoids and nuclei of cones, and weakly around the rod nuclei. A1Rs and A2ARs were clustered around ON cone bipolar cell terminals and present in the OFF lamina of the INL but were not expressed on mixed rod/cone response bipolar cell terminals. A2BR-immunoreactivity was mainly localized to the Müller cells, while A3Rs were found to be expressed in retinal ganglion cells of the GCL, INL, ONL, and OS. In summary, all four adenosine receptor subtypes were localized in the zebrafish retina and are in agreement with expression patterns shown in retinas from other species.