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The Journal of Neuroscience, April 12, 2006, 26(15):3908-3917; doi:10.1523/JNEUROSCI.4891-05.2006

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Cellular/Molecular
Random Wiring in the Midget Pathway of Primate Retina

Patricia R. Jusuf, Paul R. Martin, and Ulrike Grünert

National Vision Research Institute of Australia and Department of Optometry and Vision Sciences, The University of Melbourne, Carlton, Victoria 3053, Australia

Correspondence should be addressed to Ulrike Grünert, National Vision Research Institute of Australia, Corner of Keppel and Cardigan Streets, Carlton Victoria 3053, Australia. Email: ugrunert{at}optometry.unimelb.edu.au

The present study addresses the questions of how topographically organized neuronal populations are connected, and whether there is anatomical evidence for color-selective wiring in retinal pathways for red–green color vision. The connectivity of OFF midget bipolar and OFF midget ganglion cells was studied in the peripheral retina of dichromatic ("red–green color blind") and trichromatic ("color normal") marmosets (Callithrix jacchus). Midget bipolar cells were identified immunohistochemically. Midget ganglion cells were retrogradely labeled 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. Nearly all bipolar terminals investigated show regions of colocalization (areas of presumed synaptic contacts) with ganglion cell dendrites. This contact area makes up 14% of the axon surface area for a typical midget bipolar cell. The output from individual midget bipolar axons is often shared between midget ganglion cells so that, on average, <70% of the axon terminal area of a midget bipolar cell shows overlap with the dendritic field of a given midget ganglion cell. We conclude that there is no morphological evidence of red–green color selectivity in the connections between midget bipolar and midget ganglion cell mosaics. Furthermore, the results suggest that convergence is based on local interactions between axons and dendrites rather than cell-by-cell recognition between members of each mosaic.

Key words: color vision; parvocellular pathway; color selectivity; midget bipolar cells; midget ganglion cells; New World monkey

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Received Nov. 15, 2005; revised Feb. 6, 2006; accepted March 2, 2006.

Correspondence should be addressed to Ulrike Grünert, National Vision Research Institute of Australia, Corner of Keppel and Cardigan Streets, Carlton Victoria 3053, Australia. Email: ugrunert{at}optometry.unimelb.edu.au

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				P. Buzas, E. M. Blessing, B. A. Szmajda, and P. R. Martin Specificity of M and L Cone Inputs to Receptive Fields in the Parvocellular Pathway: Random Wiring with Functional Bias J. Neurosci., October 25, 2006; 26(43): 11148 - 11161. [Abstract] [Full Text] [PDF]

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