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.