MAPK3 and diabetes mellitus: Synaptophysin protein is decreased in the retina of the streptozotocin (STZ)-induced diabetes model through the ROS-extracellular signal-regulated kinase 1 and 2 (ERK1/2) suggesting the involvement of cross talk between mitogen-activated protein kinases (MAPK) pathway signals and neurodegeneration in the diabetic retina [3, 21].