Cone photoreceptor recovery after experimental detachment and reattachment: an immunocytochemical, morphological, and electrophysiological study.

Purpose: To compare the morphologic and functional recovery of the retina after detachment and reattachment in an animal with a cone-dominant retina, the ground squirrel.
Methods: Ground squirrel (Spermophilus beecheyi) retinas were detached for 1 day and reattached for 7, 35, or 96 days (n = 2, each time point). Flicker ERGs were recorded 1 day after the detachment and at various times after reattachment. Contrast-response functions were measured for isochromatic modulation and for selective modulation of short-wavelength-sensitive (S) and middle-wavelength-sensitive (M) cones. At the end of the experiment, retinas were prepared for light microscopy or immunocytochemical staining with antibodies to rod opsin, S and M cone opsins, cytochrome oxidase, synaptophysin, glial fibrillary acidic protein (GFAP), cellular retinaldehyde-binding protein (CRALBP), interphotoreceptor-binding protein (IRBP), and peanut agglutinin lectin (PNA). Photoreceptor density maps were created from wholemount preparations labeled with biotinylated PNA and anti-S cone opsin. Cell counts of photoreceptor nuclei and cone outer segments (OS) were compared with flicker ERG data. Cell death was examined by the TUNEL method.
Results: Reattachment stopped photoreceptor cell death and reversed the disruption of interphotoreceptor matrix as well as the redistribution of Müller cell proteins. It also activated some astrocytes based on anti-GFAP staining. S- and M-cone OS showed a gradual recovery in length after reattachment, and this recovery continued to the longest time points examined. ERG contrast gains also recovered after reattachment, but these reached asymptotic levels by approximately a week after reattachment. There were significant correlations between outer nuclear layer (ONL) cell counts and ERG contrast gains. No differences were noted in the indices of recovery of M and S cones.
Conclusions: The ERG can be used to follow specifically the changes in the retina that occur after retinal detachment and reattachment.