Figure 7. Retinal stratification, optic nerve myelination, and RGC central projections appear normal in NgR123^−/− mice.

(a) Sections of adult wildtype (WT) and Nogo receptor triple mutant (NgR123^−/−) mouse retina were subjected to in situ hybridization with digoxigenin–labeled cRNA probes specific for NgR1, NgR2, and NgR3 transcripts. All three receptors are strongly expressed in the ganglion cell layer (arrow) and the inner nuclear layer, but are absent from the outer nuclear layer of the retina. No signal was detected on parallel–processed sections of NgR123^−/− retina. (b) Hoechst 33342 nuclear staining, as well as anti–calbindin and anti–calretinin immunolabeling, of adult WT and NgR123^−/− retina did not reveal any noticeable differences in retinal organization among the two genotypes. (c) Toluidine blue labeling of epon–embedded adult WT and NgR123^−/− optic nerve cross sections reveals a comparable number of axons and degree of myelinated fibers. (d–f) The fidelity of RGC central projections in six–week–old WT and NgR123^−/− mice was assessed by anterograde fiber tracing. Five days after injection of Alexa 594–conjugated Cholera Toxin β into the right eye and Alexa 488–conjugated Cholera Toxin β into the left eye, mice were sacrificed, perfused, and brain sections analyzed by fluorescence microscopy. Right eye (red) and left eye (green) RGC projections to the (d) superior colliculus, (e) suprachiasmatic nucleus and (f) lateral geniculate nucleus in NgR123^−/− mice are indistinguishable from age–matched WT controls. Scale bar: a, b, 80μm; c, 5μm; d, 100μm; e, f, 60μm.