NPY and retinal ischemia: Calbindin (Calb) is expressed in amacrine and horizontal cells of the rat retina and was downregulated after retinal ischemia (Figure 3a).29 Amacrine cells (ACs) also express neuropeptide Y (Npy), vasoactive intestinal polypeptide (Vip) and tyrosine hydroxylase (Th).30, 31, 32 In the postischemic retina of P2Y1R-KO mice, only the expression of Ppp2ca, the gene of the α-isoform of the catalytic subunit of the protein phosphatase 2 (PP2A), was markedly decreased (Figure 3a).