IMMUNOCYTOCHEMICAL LOCALIZATION OF BASIC FIBROBLAST GROWTH-FACTOR ANDGLIAL FIBRILLARY ACIDIC PROTEIN AFTER LASER PHOTOCOAGULATION IN THE ROYAL-COLLEGE OF SURGEONS RAT

Purpose: Argon laser photocoagulation slows photoreceptor degeneration in the Royal College of Surgeons (RCS) rat, as does intravitreal inje ction of basic fibroblast growth factor (bFGF). We hypothesize that up -regulation of retinal bFGF is a consequence of laser lesioning in RCS rats,Therefore, we examined the localization of bFGF after laser and correlated this with Muller cell glial fibrillary acidic protein (GFAP ) expression, which is known to increase after injury. Methods: A tota l of 34 RCS rats at postnatal day 23 were anaesthetized (ketamine 40 m g/kg) and their retinas were irradiated with a grid pattern of 40 non- overlapping argon green lesions with a power of 120 mW for 0.2 s using a 50 mu m spot size. At 0, 6, 12, 24 and 48 h and 7, 14 and 21 days p ost-lesion, rats were anaesthetized and their eyes were enucleated and cryostat sectioned and the sections were processed using either an an tibody to bFGF or GFAP using the standard avidin-biotinylated peroxida se complex method. Five age-matched RCS rats without laser lesions ser ved as controls. Results: Basic fibroblast growth factor immunoreactiv ity (IR) was normally located within cells in the ganglion cell layer, inner nuclear layer and in retinal pigment epithelium cells and in th e extracellular matrix/cell membranes of the outer nuclear layer (ONL) , in lasered retinas, there was elevated bFGF-IR in the coagulated out er segments for the first 24 h. Retinal blood vessels/Muller cells/ast rocytes were moderately labelled in and near each lesion immediately a fter lesion and became more intense after 48 h and persisted for at le ast 21 days. There was an elevation of bFGF-IR in the ONL on the lesio n flanks at 14 days. Muller cell GFAP-IR was first detected at 6h post -lesion and spread for a considerable distance beyond the lesion site. At 7 and 14 days, Muller cells at the lesion site had sprouted, while those on the flanks were still GFAP-IR. Conclusions: Following laser lesion there was an increase in bFGF at the lesion core only for the f irst 24 h. However; elevated levels of bFGF were observed in the ONL a t 14 days, which extended into the lesion flanks for a similar distanc e to that over which increased photoreceptor survival is found. These results provide support for the hypothesis that laser lesions induce b FGF and this may be the mechanism whereby photoreceptors are spared. M uller cell activation is consistent with growth factor stimulation, bu t was more widespread than the bFGF changes in ONL However; blood vess el labelling was similarly widespread and so the responses may be link ed between Muller cell GFAP reaction and blood vessel bFGF localizatio n after laser lesions.