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R.G. Pourcho, D.V. Pow, B. Fyk-Kolodziej; Localization of Glutamate Transporters GLT1-B and EAAC1 in the Cat Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5165.
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Purpose: To determine the cellular and subcellular distribution of the GLT1-B and EAAC1 transporters in the cat retina. Methods: Pre-embedding immunocytochemical techniques were used to localize the transporters by both light and electron microscopy in the cat retina. Results: Staining for GLT1-B was observed in the somas and axon terminals of cone photoreceptors as well as in numerous bipolar cells and some ganglion cells. Prominent among the bipolar cells was a subpopulation of OFF-cone bipolar cells which make flat contacts not only with cone pedicles but also with rod spherules. Such contacts have not been visualized previously in the cat but have been reported in the rodent retina (Hack et al., 1999). In the cat, as in the rat, these dendrites express the AMPA-type glutamate receptor GluR1. Other GLT1-B positive bipolar cells included both OFF- and ON-type cone bipolars as well as rod bipolar cells. The staining in rod bipolar cells was concentrated in their somas and initial portions of their axons but was not evident in the dendrites or axon terminals. In contrast to GLT1-B, staining for EAAC1 was observed in both A- and B-type horizontal cells as well as in a number of amacrine cells and ganglion cells. Staining in the IPL was dominated by the processes of large alpha and beta type ganglion cells. These processes were often seen as the single stained element at cone bipolar dyad synapses where the other post-synaptic process was unstained. Conclusions: These findings demonstrate the high level of specificity of glutamatergic pathways which includes the discrete localizations not only of receptor molecules but also of transporters. In addition, the visualization of direct contacts between rod photoreceptors and GLT1-B positive cone bipolar cells provides a morphological basis for the mixing of rod and cone signals in the cat retina.
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