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U. Grunert, P.R. Jusuf, P.R. Martin; Random Wiring in the Midget Pathway of Primate Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2308.
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To study determine whether there is anatomical evidence for color selective wiring in retinal pathways for red–green color vision.
The connectivity of midget bipolar and midget ganglion cells was studied in peripheral retina of dichromatic (red–green color blind) and trichromatic (color normal) marmosets (Callithrix jacchus). Midget bipolar cells (n = 453) were identified immunohistochemically. Midget ganglion cells (n = 38) were retrogradely labelled from the lateral geniculate nucleus and photofilled.
Comparable results were obtained from all retinas studied. Between 3 and 16 bipolar terminals converge onto each ganglion cell. The terminals of most bipolar cells (91%) show regions of colocalisation (areas of presumed synaptic contacts) with ganglion cell dendrites. This contact area makes up about 14% of the axon surface area for a typical midget bipolar cell (14.6 ± 6.7% SD in dichromat; 13.3 ± 8.0% SD in trichromat). The output from individual midget bipolar axons is often shared between midget ganglion cells, so that on average, less than 70% of the axon terminal area of a midget bipolar cell shows overlap with the dendritic field of a given midget ganglion cell (mean 63.8 ± 35% SD in dichromat; 69.5 ± 32.7 % SD in trichromat).
There is no morphological evidence of red–green color selectivity in the connections between midget bipolar and midget ganglion cell mosaics. These results suggest that convergence is based on local interactions between axons and dendrites rather than cell–by–cell recognition between members of each mosaic.
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