EFFECTS OF AXOTOMY AND INTRAOCULAR ADMINISTRATION OF NT-4, NT-3, AND BRAIN-DERIVED NEUROTROPHIC FACTOR ON THE SURVIVAL OF ADULT-RAT RETINALGANGLION-CELLS - A QUANTITATIVE IN-VIVO STUDY

Purpose. To investigate in vivo the survival of retinal ganglion cells (RGC) 4 to 14 days after optic nerve (ON) transection alone or in com bination with a single intraocular injection of neurotrophin-4 (NT-4), neurotrophin-3 (NT-3), or brain-derived neurotrophic factor (BDNF). M ethods. In adult rats, RGCs were labeled with fluorogold (FG) applied to their main targets in the brain. Seven days later, the left ON was intraorbitally transected, and, in several groups of animals, the left eye received a sham injection or was injected with 5 mu l of 1% bovin e serum albumin-phosphate-buffered saline alone or containing 5 mu g o f NT-4, NT-3, or BDNF. Four, 5, 7, 9, 12, and 14 days after ON transec tion, the retinas were examined under fluorescence microscopy to estim ate RGC survival. Results. In control retinas, the mean densities (cel ls/mm(2) +/- SEM) of FG-labeled RGCs were 2421 +/- 55 (n = 20). Four d ays after axotomy, the densities of RGCs were similar to those observe d in control retinas, but 5 and 7 days after axotomy, the mean densiti es had decreased to 2028 +/- 63 (n = 6) and 1568 +/- 50 (n = 6), respe ctively. In the group of retinas with sham injection, with vehicle alo ne or with NT-3, RGC densities also decreased by 7 days to 1261 +/- 71 (n = 5), 1506 +/- 98 (n = 10), and 1474 +/- 125 (n = 4), respectively . However, similar densities to those observed in control retinas were observed 7 days after ON transection in the groups of retinas treated with NT-4 (2505 +/- 91; n = 7) or BDNF (2380 +/- 74; n = 7). Fourteen days after axotomy, RGC densities decreased to 521 +/- 39 (n = 10). C omparable densities were found in the groups that underwent axotomy an d either sham injection (533 +/- 51; n = 5), injection of vehicle (588 +/- 19; n = 10), or NT-3 treatment (634 +/- 62; n = 6). However, at t his time, higher densities were observed in the groups treated with NT -4 839 +/- 39 (n = 8) or BDNF 1321 +/- 120 (n = 7). Conclusions. Axoto my-induced RGC death first appears by day 5 and reaches 80% of the ori ginal RGC population by day 12. NT-4 and BDNF administered intraocular ly at the time of axotomy exert a neuroprotective effect on axotomy-in duced RGC death, thus increasing the population of surviving RGCs and delaying the onset of axotomy-induced RGC death by approximately 3 day s. Intraocular administration of NT-3 did not modify the survival of R GCs after injury.