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P. R. Jusuf, S. C. S. Lee, E. S. Terenyi, K. S. Cheong, J. Hannibal, U. Grunert; Immunohistochemical Analysis of Melanopsin Containing Ganglion Cells in Marmoset Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2807.
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© ARVO (1962-2015); The Authors (2016-present)
To analyse the distribution and synaptic connectivity of melanopsin immunoreactive ganglion cells in the retina of the common marmoset (Callithrix jacchus).
Marmoset retinas were processed with antibodies against melanopsin, C-terminal binding protein 2 (CtBP2 to identify synaptic ribbons), gephyrin (to identify inhibitory synapses), or CD15 (diffuse bipolar DB6 cells). High resolution fluorescent deconvolution light microscopy was used for the analysis.
Melanopsin immunoreactive ganglion cells in marmoset retina are large, sparse wide-field cells comparable to those described in human and macaque. They are present across the retina with a peak density of 54 cells/mm2 in central and less than 2 cells/mm2 in peripheral retina. The dendritic field diameter increases with eccentricity (200 µm to 756 µm). Approximately 55% of the somas are displaced to the inner nuclear layer. The dendrites of most (88%) melanopsin cells stratify close to the inner nuclear layer. The remainder stratify close to the ganglion cell layer. The input from bipolar cells was estimated for 10 cells by counting the number of CtBP2 immunoreactive puncta that were colocalised with labelled ganglion cell dendrites. The input from amacrine cells was estimated for two cells by counting the number of colocalised gephyrin immunoreactive puncta. Presumed bipolar input was on average 3 ± 1.4 puncta/100 µm of dendrite and presumed amacrine input was on average 9 ± 3.8 puncta/100 µm. The total number of colocalised puncta per cell ranged from 43 to 285 for CtBP2 and from 267 to 540 for gephyrin. For one melanopsin immunoreactive cell, we found 365 presumed contacts with DB6 axon terminals.
Melanopsin containing ganglion cells receive input from bipolar and amacrine cells, with DB6 possibly providing the bipolar input to inner stratifying cells as suggested for macaque (Dacey et al., 2006, ARVO E-abstract 3111). Thus, melanopsin containing cells are likely involved in retinal circuits arising from cone or rod photoreceptors in addition to their intrinsic photosensitive response.
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