Figure 9. Brn3c RGCs axons project to the thalamic reticular nucleus.

a–f, Coronal sections (200 μm thickness) at −1.7 to −1.9 mm from bregma (Paxinos mouse atlas) through the brains from mice with indicated genotypes. Genotypes in which the Brn3c locus drives Cre expression are: (a) CAG:Dre; Brn3c^CKOCre/WT; ROSA26^AP/WT, (b) Brn3c^Cre/WT; Brn3a^CKOAP/WT and (c) Brn3c^Cre/WT; Brn3b^CKOAP/WT. Genotypes in which retinal-derived Brn3a-c RGC expression is driven by Rax:Cre are: (d) Rax:Cre; Brn3c^CKOAP/WT, (e) Rax:Cre; Brn3a^CKOAP/WT and (f) Rax:Cre; Brn3b^CKOAP/WT. Given the thickness and slight variations in the cutting angles, the sections are close but not perfect matches, but are representative of the entire region, as the entire brain was cut on the vibratome, stained and imaged. Arrowheads indicate the dLGN; * indicates the cerebral peduncle, basal part; ot is the optic tract; Arrows indicate RGC projections to the thalamic reticular nucleus. g–h, Coronal sections (150 μm thickness) at −1.9 mm (g) and −2.3 mm (h) from bregma (Paxinos mouse atlas) through brains from Rax:Cre; Brn3c^CKOAP/WT mice. From left to right, panels show AP histochemistry, ChTB-A488 labelling of RGC projections, anti-Parvalbumin immunostaining, and merged images. For merged images, AP-stained sections were imaged in grayscale and inverted, before merging with the green, red and blue (DAPI nuclear stain) images. Arrowheads point to dLGN, white arrow to the Brn3c⁺ RTN projection. v indicates vLGN, r indicates the RTN. Marquee regions in the Parvalbumin channels are shown in the enlarged insets in the bottom left corners. For each genotype, experiments were performed on three mice. Scale bars: a–f = 1 mm, g–h = 0.5 mm.