Figure 7. Increased counts of TH-positive cells in the IRBP KO mice compared to the WT mice. Flatmounting of the retina and immunostaining for tyrosine hydroxylase (TH) was conducted on P30 wild-type (WT) mouse eyes (A) and knockout (KO) mouse eyes (B). Substantially more TH-positive cells were evident in the interphotoreceptor retinoid-binding protein (IRBP) KO retina than in the WT retina. C: There was about a 25% increase in the number of TH-positive cells in the inner nuclear layer (INL) of the IRBP KO mouse retina compared to the WT mouse retina at P30. The pattern of excessive TH-positive cells was not evident until P26 and later. This inverse relationship coincides closely with the pattern of a rapid burst of cell death in the ONL of the IRBP KO mouse.