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Hannah R. Joo, Beth B. Peterson, Toni J. Haun, Dennis D. Dacey; A Novel Large-Field Cone Bipolar Cell Type In The Primate Retina: Evidence For Selective Cone Connections. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4119.
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© ARVO (1962-2015); The Authors (2016-present)
In the primate, diffuse cone bipolar cells contact multiple cone types non-specifically, midget bipolars contact primarily single L or M cones and blue cone bipolars selectively contact S cones. Cone bipolars with very large dendritic fields have been observed previously but their identity, morphology and cone connectivity is unknown. Here we provide a description of a novel ‘giant’ bipolar cell and its cone connections in the macaque monkey retina.
The axonal field area and stratification, and the dendritic field area and branchpoint number were measured in 69 giant bipolar cells observed in Golgi-stained retinal wholemount and vertical sections. Cone inner segment position was used to estimate the number of cone pedicles contacted by individual giant cells.
Giant bipolar cells have very large, sparse dendritic trees and large axonal arbors that co-stratify with a diffuse bipolar, the DB4, near the center of the inner plexiform layer (mean % IPL depth ± SD = 57±2.6%; n = 27). The giant bipolar cells were thus distinguished from the two other bipolar types with large dendritic arbors, the DB6 and blue cone bipolar whose axons stratify at the inner border of the IPL. Critically, the giant cells contact only a subset of cones within their dendritic field (mean % of cones contacted ± SD = 52±18%; range = 27-82%; n = 6) and were observed to contact the same cones (presumed L or M) as invaginating midget bipolar cells while bypassing S cone pedicles being contacted by neighboring blue cone bipolar cells. Multiple dendrites from single or neighboring giant cells often extend over some distance, bypassing many pedicles before converging and terminating onto the same cone.
Axonal stratification and dendritic and axonal morphology distinguish the giant cells from all previously recognized bipolar cell types. Giant bipolar cells only contact on average half the cones in their dendritic field. The range of percentage of cones contacted along with dendritic convergence onto the same cone indicate giant cells may selectively target the locally patchy L or M cone submosaic.
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