Hypoglycemia induces general neuronal death, whereas hypoxia and glutamate transport blockade lead to selective retinal ganglion cell death in vitro.

OBJECTIVE

To examine the impact of experimental ischemia and interruption of glutamate transport on retinal neuronal cell, especially retinal ganglion cell (RGC), survival in vitro.

METHODS

Cell cultures were prepared from adult pig retinas and maintained under different experimental conditions of increasing hypoglycemia, environmental hypoxia (delayed postmortem period or atmospheric PO2 <2%), or chemical hypoxia (potassium cyanide), or in the presence of glutamate transporter blockers L-trans-pyrrolidine-2,4-dicarboxylic acid (tPDC) and L(-)-threo-3-hydroxyaspartic acid (THA), or the glutamine synthetase inhibitor methionine sulfoximine (MS). After 48 hours, cells were returned to standard culture conditions and allowed to develop for 5 days, when they were fixed and immunostained with different retinal neuronal phenotypic markers.

RESULTS

Control normoxic cultures contained large numbers of immunocytochemically identified photoreceptors (PRs), bipolar cells (BCs), amacrine cells (ACs), and RGCs after 7 days in vitro. A 24-hour postmortem delay before culture led to significant reductions in all types (40%-70%), proportionately greater in ACs and RGCs. Lowering of sugar levels also led to increased losses in all cell types, whereas potassium cyanide treatment deleteriously affected only ACs and RGCs. Ambient hypoxia led to consistent reductions only in the number of RGCs, which were exacerbated by addition of high concentrations of glutamate. Inclusion of glutamate receptor antagonists had a partial protective effect against RGC loss. Treatment with tPDC and THA also led to selective RGC death, but MS had no effect on any cells.

CONCLUSIONS

Different components of the ischemic pathologic process (hypoxia, hypoglycemia, glutamate transport failure) lead to distinctly different patterns of neuronal loss in adult retina in vitro. RGCs are especially vulnerable, corresponding to their in vivo susceptibility. These data may suggest neuroprotective strategies for limiting retinal damage during ischemia.