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J. Verweij, E.P. Hornstein, P.H. Li, J.L. Schnapf; Gap Junctional Coupling Between Rods in the Primate Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4629.
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Purpose: Rod photoreceptors are electrically coupled through gap junctions in a variety of cold–blooded vertebrates. Gap junctions have also been observed between rods in electron micrographs of mouse and guinea pig retina, but not primate retina. Are primate rods electrically coupled to each other through gap junctions as well, or are they the exception to the rule? Methods: Whole–cell recordings were made from individual rods in isolated retina of macaque and squirrel monkeys. Photovoltage was measured in response to 50–150 flashes of dim diffuse light. Statistical fluctuations in response amplitudes were analyzed. Single rods were filled with Neurobiotin to examine dye coupling. Results: The distribution of response amplitudes in most rods could be accounted for by the Poisson statistics of photoisomerization in uncoupled rods. In 20% of rods however, the response amplitude distributions were inconsistent with the expected number of photoisomerizations in single rod outer segments. The distribution instead was consistent with the pooling of signals from 5–7 rods. Of the 38 rods injected with Neurobiotin, 60% were dye–coupled to neighboring rods. The average number of dye–filled rods in a coupled pool was 4 (range 2–8). Conclusions: Some rods in primate retina are dye–coupled and share photon signals with neighboring rods. Coupling presumably occurs via rod–rod gap junctions, although none have been observed so far either with electron microscopy or with connexin immunohistochemistry. Further anatomical and physiological studies are needed to determine the strength and relevance of rod–rod coupling under various physiological conditions.
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