BDNF Rescues RGCs But Not Intrinsically Photosensitive RGCs in Ocular Hypertensive Albino Rat Retinas.

Purpose: To study the responses of the general population of retinal ganglion cells (Brn3a(+)RGCs) versus the intrinsically photosensitive RGCs (melanopsin-expressing RGCs [m(+)RGCs]) to ocular hypertension (OHT), the effects of brain-derived neurotrophic factor (BDNF) on the survival of axonally intact and axonally nonintact RGCs, and the correlation of vascular integrity with sectorial RGC loss.

Methods: In Sprague-Dawley rats, 5 μg BDNF or vehicle was intravitreally injected into the left eye followed by laser photocoagulation of the limbal tissues. To identify RGCs with an active retrograde axonal transport, Fluorogold was applied to both superior colliculi 1 week before euthanasia (FG(+)RGCs). Retinas were dissected 12 or 15 days after lasering and immunoreacted against Brn3a (to identify all RGCs except m(+)RGCs), melanopsin, or RECA1 (inner retinal vasculature).

Results: Ocular hypertension resulted at 12 to 15 days in sectorial loss of FG(+)RGCs (78%-84%, respectively) while Brn3a(+)RGCs were significantly greater, indicating that a substantial proportion (approximately 21%-26%) of RGCs with their retrograde axonal transport impaired survive in the retina. Brain-derived neurotrophic factor increased the survival of Brn3a(+)RGCs to 81% to 67% at 12 to 15 days, respectively. The inner retinal vasculature showed no abnormalities that could account for the sectorial loss of RGCs. At 12 to 15 days, m(+)RGCs decreased to approximately 50% to 51%, but this loss was diffuse across the retina and was not prevented by BDNF.

Conclusions: The responses of m(+)RGCs against OHT-induced retinal degeneration and neuroprotection differ from those of Brn3a(+)RGCs; while OHT induces similar loss of Brn3a(+)RGCs and m(+)RGCs, Brn3a(+)RGCs are lost in sectors and can be rescued with BDNF, but m(+)RGCs do not respond to BDNF and their loss is diffuse.