Activation of ERK-1 (MAPK1). A. Western blots were probed with anti-ERK-1 (pThr202/pTyr204) antibody. There was constitutive activation prior to optic nerve crush. However, the phosphorylation ratio (pERK/ERK) increased further at 360 min although the total ERK extracted was lower. B. Graph of the data in A normalized to the total ERK-1 protein. C-F Immunohistochemistry of activated ERK-1, at 0, 30 min, 60 min, and 360 min (6 hr) after optic nerve crush, respectively. Increased labeling of cells in the OPL (down arrows) are particularly evident at 30 min as well as decreased labeling of Muller cells that extend the from the ONL to the GCL (arrowheads). Also note that there is immunolabeling for pERK-1 in the inner stratum of the inner plexiform layer at 30 min and 6 hrs (up arrows) and labeling in the ganglion cell layer at 60 min (arrowheads). The grayscale inset in C shows the staining of the Muller cell marker glutamine synthase. Red = pERK-1, Blue = DAPI.