Expression of ciliary neurotrophic factor activated by retinal Müller cells in eyes with NMDA- and kainic acid-induced neuronal death.

Purpose: To elucidate the role of retinal Muller cells in N-methyl-D-aspartate (NMDA)- or kainic acid (KA)induced retinal damage.
Methods: In experimental eyes, NMDA or KA was injected into the vitreous of rat eyes. Immunohistochemistry and western blot analysis were conducted to elucidate expression and localization of glial fibrillary acidic protein (GFAP) and ciliary neurotrophic factor (CNTF). In addition, the neuroprotective effects of CNTF were calculated by counting cells in the ganglion cell layer (GCL) and by measuring the thickness of the various retinal layers.
Results: Morphometric analysis of retinal damage in NMDA- and KA-injected eyes showed significant cell loss in the GCL and thinning of the inner plexiform layer (IPL) of the retina, but not of other retinal layers. Immunohistochemistry demonstrated disappearance and/or decrease in immunoreactivities of calbindin- and calretinin- positive cells and their neurites and upregulated expression of both GFAP and CNTF in experimental eyes. Western blot analysis showed an increase in protein expression for CNTF in retinas of experimental eyes. Confocal images and sequential localization demonstrated colocalization of CNTF and GFAP in the inner retinal layer and possibly in Muller cells. In addition, pretreatment with CNTF (1 microg) before the intravitreal injection of NMDA (or KA) demonstrated that CNTF has neuroprotective effects against NMDA- or KA-induced neuronal death in the retina.
Conclusions: These studies revealed the upregulated expression of CNTF and GFAP in Muller cells in response to NMDA- and KA-induced neuronal death, suggesting that production of CNTF in Muller cells may be a part of the endogenous neuroprotective system in the retina.