Etanercept Prevents Glaucomatous Neurodegeneration Figure 5. Etanercept prevents optic nerve degeneration after OHT induction. A–C, High magnification light micrographs of cross sections through rat optic nerve. EVC leads to diminished axon density, enlarged axons (white arrowhead), and degenerating axon profiles (black arrow in B). D, Bar graph showing axon densities in the various groups. Data are expressed as the mean 6 SEM. Mann-Whitney U test, **P,0.01 compared between sham-operated control and vehicle-treated OHT, {{P,0.01 comparing OHT cases treated with vehicle vs. Etanercept (n = 6 for each group). Original magnification: 6100; Scale bar, 5 mm. OHT, Ocular hypertension; Etan., Etanercept. doi:10.1371/journal.pone.0040065.g005 other indications, is effective in rescuing RGCs from OHT- induced death. Since maintaining elevated IOP is crucial in any model of glaucoma, Etanercept was given systemically rather than intravitreally, and did not affect IOP (Fig. 1). Another technical issue is that cauterizing the episcleral vein may lead to retinal ischemia, which can also result in RGC death [30,31]. Ischemia and hypoxia have been implicated in the development of RGC death in patients with glaucoma [18,32], and thus the model of chronic OHT used here may mimic multiple features of the clinical disorder. Retinal microglia are resident macrophages derived from myeloid progenitor cells that are capable of phagocytic activity in multiple conditions [33,34] that include aging, hypoxia, neurodegeneration, and injury. In all of these instances, microglia transform from a resting state with a ramified morphology to an activated phenotype [35] that retract their processes and exhibit a rounded cell body. Iba-1 antibody is a microglial/macrophage marker that is expressed in both the resting and activated states [36]. Immunohistochemical staining on whole-mounts showed increased numbers of amoeboid, activated Iba-1-positive microglia PLoS ONE | www.plosone.org 6 July 2012 | Volume 7 | Issue 7 | e40065