Fig. 8. Inhibition of TGFßRI signaling increases proliferation in the central P6 retina. Postnatal day 5.5 rat pups were given intraocular injections of either DMSO (control) or 40 nanomoles SB431542, small molecule inhibitor of the TGFßRI kinase domain. Pups were injected with BrdU 12 hours later, at P6. (A) A section located at the level of the optic nerve (ON) shows few cells are BrdU⁺ (green) after intraocular injection with DMSO. (B) SB431542-treated retinas contain numerous BrdU-labeled (green) cells in the region of the optic nerve (ON). (C) Quantification of the number of BrdU⁺ cells in sections of the retina adjacent to the optic nerve show DMSO-treated control animals (n=6) average 105 (±27) BrdU⁺ cells/mm² central retina, whereas SB-431542 treated animals (n=5) average 240 (±40) BrdU⁺ cells/mm² central retina. ^**P<0.01. Scale bar: 100 µm.