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F. Pan, M. Stephen; Dye Coupling of Horizontal Cells in the Primate Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3046.
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In the monkey retina, there are two kinds of horizontal cells, H1 and H2. We filled both types with Neurobiotin to examine their fine structure and dye-coupling properties.
Horizontal cell somas of the macaque retina were targeted by prelabeling with DAPI. H1, H2 and H1 axon terminals were injected with Neurobiotin. Tissues were then fixed, stained with streptavidin and incubated with antibodies against mGluR6, cone arrestin or Ribeye. The material was analyzed by multi-channel confocal microscopy.
After filling H1 cells, a large coupled mosaic of H1 cells was recovered. Multiple axons ran from the central heavily stained somas for distances in excess of 1mm but the axon terminals could not be observed. The dendritic terminals of H1 cells contacted red/green cone pedicles with occasional sparse contacts with blue cone pedicles. At the cone pedicle, H1 terminals were interspersed with mGluR6 puncta associated with ON cone bipolar cells. H2 cells were also dye-coupled. They had larger dendritic fields and a lower density. The dendritic terminals of H2 cells preferentially contacted blue cone pedicles but there were additional contacts with all cones within the dendritic field. These observations confirmed previous work on primate horizontal cells (Dacey et al., 1996; Goodchild, Chan and Grünert, 1996). Because the length of H1 axons prevented the recovery of H1 axon terminals, we filled them directly at a distal level in the OPL. When a single axon terminal was filled, we observed a faint mosaic of coupled dendrites which appeared to contact every rod spherule. This indicates that H1 axon terminals in the primate retina are independently coupled.
In the primate retina, there are three independently coupled horizontal networks in the OPL; H1, H2 and H1 axon terminals. We have not yet observed the axons of H2 horizontal cells.
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