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D. W. Marshak, C. Rangel, J. O' Brien; Gap Junctions Between AII Amacrine Cells and Blue Cone Bipolar Cells in Macaque Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1630.
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The goal of these experiments was to identify the source of rod input to blue cone bipolar cells and their postsynaptic targets in primate retina.
Macaque retinas were fixed with 4% paraformaldehyde, and 50-70 µm vertical sections were cut with a vibratome. The sections were incubated in goat anti-calretinin, an AII amacrine cell marker, rabbit anti G6-gly, a blue cone bipolar cell marker and mouse monoclonal antibody to connexin 36, the gap junction protein expressed in AII cells. The tissue was then incubated in affinity-purified secondary antibodies raised in donkeys, each with a different fluorophore. The images were acquired using a confocal laser scanning microscope.
Antibodies to the glycine-extended gastrin-cholecystokinin precursor, G6-gly, labeled blue cone bipolar cells. They had long dendrites that contacted a subset of cone pedicles and axons that descended to stratum 5 (S5) of the inner plexiform layer (IPL). They could readily be distinguished from labeled amacrine cell processes in S4 based on their depth of stratification. Antibodies to calretinin labeled AII amacrine cells, which had distinctive, lobular dendrites in the distal half of the IPL and a dense plexus of dendrites in the proximal half. Puncta labeled with antibody to connexin 36 were distributed in the IPL as described previously in other mammals. In S5, there were appositions between S cone bipolar cell axons and dendrites of AII amacrine cells, and puncta containing immunoreactive connexin 36 were found at these sites. These contacts were followed through single optical sections to rule out the possibility that they resulted from superposition.
Contacts were observed between AII amacrine cell dendrites and axon terminals of blue cone bipolar cells in macaque retina. Because these were associated with puncta containing immunoreactive connexin 36, these are likely sites of gap junctions. These findings suggest that blue cone bipolar cells receive highly sensitive, sign-conserving input via the primary rod pathway.
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