Characterization of a Culture System for Rat Retinal Ganglion Cells: Towards a Screen for Potential Neuroprotective Compounds

Abstract

The retina is the target of several diseases, the most common of which include macular degeneration, retinal ischemia, diabetic retinopathy, and glaucoma. Glaucoma alone affects about 67 million individuals worldwide (Luo et al., 2001). In glaucoma, as well as other diseases of the optic nerve, retinal ganglion cell (RGC) death is the final pathway (Kawasaki et al., 2000). It is thought that elevated levels of glutamate in the eye (as reported in glaucoma patients, Dreyer et al., 1996) are directly involved in acute and chronic neurodegenerative processes. Ionotropic glutamate receptors (iGluRs) are found on the retina and can be divided into N-methyl D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA), and kainate (KA) receptors (Meldrum, 2000). MK-801 is a specific, non-competitive antagonist that acts at the channel of the NMDA receptor (this compound is neuroprotective but with side effects similar to LSD). Activation of KA can also cause excitotoxicity in cells (Watkins and Collingridge, 1989). Acetylcholine receptors (AChRs), specifically, nicotinic AChRs (nAChRs) have been found in the inner retina and on RGCs (Baldridge, 1996; Kittila & Massey, 1997). There is already a strong base of research suggesting that both nicotine and α7-selective compounds are neuroprotective (e.g. ABT-418, Donnelly-Roberts et al., 1998) and a selective α7 compound would be highly desired to avoid the use of nicotine. AR-R 17779 is another compound specific for the α7 nicotinic receptor (Mullen et al., 2000). This study explored the possibility that selective activation of the α7 nAChRs could have neuroprotective effects comparable to nicotine on RGCs. It was hypothesized that a viable primary culture of RGCs could be maintained and used in toxicity assays. Also, that treatment with glutamate would decrease cell viability while treatment with nicotine and AR-R 17779 would increase cell viability.