Glial Remodeling and Neural Plasticity in Human Retinal Detachment with Proliferative Vitreoretinopathy

To investigate glial remodeling and neuronal plasticity in adult human retinal detachment complicated by proliferative vitreoretinopathy (PVR) and to grade pathologic changes with a severity scoring system. Sixteen full-thickness retinectomy specimens obtained at retinal relaxing surgery for PVR were fixed in 4% paraformaldehyde immediately after excision and compared to similarly processed normal donor retinas. Agarose-embedded sections (100-microm-thick) were double labeled for immunohistochemistry by confocal microscopy, with antibodies against rod opsin and GFAP; vimentin and M/L-cone opsin; calbindin D and S-cone opsin; and cytochrome oxidase and synaptophysin. These staining patterns formed the basis of a retinal pathology scoring system, and immunohistochemistry was also used to detect CD68, neurofilaments, protein kinase C, growth-associated protein-43, and a pan-cone-specific enzymatic marker. Morphology was also assessed by light microscopy of resin-embedded semithin sections. Prolonged detachment was characterized by photoreceptor degeneration and intracellular redistribution of opsin proteins to the plasma membrane in the outer nuclear layer (ONL). Remodeling of rod synaptic terminals was characterized by terminal retraction and also by axon extension to the inner retina in most specimens. Rod bipolar cell dendrites extended into the ONL, as did fine, horizontal cell processes. Large ganglion cells showed upregulated neurofilament and GAP-43 expression, with neurites sprouting from somata and axon collaterals. Anti-cytochrome oxidase labeling of surviving inner segments was reduced but detectable in all specimens, as was anti-calbindin D labeling of horizontal and amacrine cells. All specimens demonstrated a marked upregulation of Muller cell and astrocyte expression of GFAP and vimentin. More severe degenerative changes correlated with trauma and prolonged detachment duration when scored according to this system. The neural and glial components of detached neurosensory retina complicated by PVR exhibit pathology that changes characteristically with increasing detachment severity. Even in advanced degeneration, most of the structural motifs necessary for functional recovery are retained. Evidence of remodeling in the first-, second-, and third-order neurons of detached adult human retina may represent an attempt to re-establish synaptic connectivity.