Visual stimulation enhances retrograde transport of BDNF from the superior colliculus to the retina in health and autoimmune uveitis

Experimental autoimmune uveoretinitis (EAU) shows degeneration of retinal neurons, including retinal ganglion cells (RGCs), already in its early phase. Based on our previous study demonstrating the attenuation of EAU by brain-derived neurotrophic factor (BDNF), whose retinal levels were increased by visual stimulation (VS), this study evaluated the effect of VS on BDNF protein expression in brain visual centers, its retrograde transport to the retina, and RGC survival in healthy and EAU mice. 14-day VS increased BDNF expression in the superior colliculus (SC) but not in the lateral geniculate nucleus and primary visual cortex in healthy and EAU mice compared to their unstimulated groups. Furthermore, VS increased numbers of BDNF-positive neurons and astrocytes in the retinorecipient superficial SC (sSC) in healthy and EAU mice, although stimulated EAU mice showed a modest reduction in BDNF-positive neurons compared to stimulated healthy mice. In contrast, unstimulated EAU mice exhibited a marked loss of sSC BDNF-positive neurons and astrocytes compared to unstimulated healthy mice. Additionally, VS promoted retrograde axonal transport of fluorescently labeled BDNF from the sSC to the retina, where it was detected in RGCs, inner retinal neurons, and Müller cells (MCs). These results suggest that VS-induced increases in BDNF expression in the sSC and its retrograde transport to the retina may directly affect multiple types of retinal neurons and MCs, on which BDNF can exert neurotrophic and protective effects. The overall attenuation of EAU histopathology and retinal inflammation, along with improved survival of RGCs in VS-treated EAU mice, is consistent with this suggestion.