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Felix Weltzien, Stefano Di Marco, Dario Protti, Teresa Daraio, Paul Martin, Ulrike Grunert; Immunohistochemical identification and characterization of a wide-field amacrine cell type in marmoset retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2511.
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© ARVO (1962-2015); The Authors (2016-present)
Amacrine cells are the most diverse class of retinal neurons. In primates more than 25 different types of amacrine cell have been described. Here, we analysed the morphology, density and distribution pattern of a subset of amacrine cells that express the Ca2+ binding protein secretagogin in the marmoset (Callithrix jacchus) retina.
Retinas were either subjected to standard immunohistochemistry or pre-labelled with an antibody specific for secretagogin and subsequently immunopositive cells were injected with DiI. A total of 75 DiI labeled amacrine cells was analysed.
Secretagogin immunoreactivity was present in wide-field amacrine cells with somata in the inner nuclear layer (79%), as well as displaced amacrine cells with somata in the ganglion cell layer (21%). The cell bodies of regular and displaced amacrine cells together form a regular mosaic suggesting that they form a single population. Secretagogin positive amacrine cells have a peak density of 585 cells/mm2 in central retina, which decreases to 55 cells/mm2 in peripheral retina. We estimate that in the inner nuclear layer secretagogin positive amacrine cells make up 0.3% of the total amacrine cell population in marmoset retina. Co-immunostaining with antibodies against glutamic acid decarboxylase indicate that secretagogin immunopositive cells use GABA as their neurotransmitter. The processes of secretagogin positive amacrine cells were broadly stratified in the middle two thirds of the inner plexiform layer between the dendritic strata formed by cholinergic amacrine cells. DiI injection of individual cells revealed that these cells have dendritic trees, which are decorated with small spines and large varicosities.
Our results suggest that secretagogin positive cells form a subpopulation of GABAergic amacrine cells, which reveal a close resemblance to the “spiny” amacrine cell described in macaque by Mariani (1990).
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