Purpose. To elucidate the role of glial glutamate transporters in the regulation of retinal function. Methods. We administered antisense oligonucleotides to GLAST, a glutamate transporter which is expressed in retinal Müller cells, into one eye of each rat. Sense oligonucleotides (control) were injected into the other eye over a period of 5 days, and the scotopic flash electroretinograms (ERG) recorded. To assay whether the antisense oligonucleotides caused a reduction in the expression or the activity of GLAST, we have developed a novel assay, whereby the retinas are exposed to D-aspartate, a non-endogenous substrate of glutamate transporters, then immunolabelled with specific antibodies for D-aspartate. Results. We demonstrate that antisense oligonucleotides markedly suppress the b-wave of the ERG whereas the sense oligonucleotide has little effect. Preliminary results suggest that there is a marked reduction in the uptake of D-aspartate into Müller cells in the retinas which have been exposed to the antisense oligonucleotides. Conclusion. Since suppression of glutamate uptake into Müller cells is likely to cause a rise in extracellular glutamate, this result may indicate either a subsequent excitotoxic effect of glutamate on retinal neurones or may reflect a direct perturbation of glutamatergic signalling. To verify whether this reduction in uptake of D-aspartate is due to a decline in expression of GLAST or to decreased transporter activity of GLAST, we are currently generating antibodies against each of the glutamate transporters (GLAST, GLT-1 and EAAC1). Using this multifactorial approach it should be possible to accurately ascribe physiological roles of these, and other transporters, in the mammalian retina.
|Investigative Ophthalmology and Visual Science
|Published - 1 Dec 1997