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Arnold Szabo, Akos Lukats, Klaudia Szabo, Anna Enzsoly, Agoston Szel; Immunocytochemical and Functional Analysis of TrkB Expression in the Developing Cones of the Rat Retina. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3945.
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© ARVO (1962-2015); The Authors (2016-present)
There is only controversial data in literature if photoreceptors express the TrkB neurotrophin receptor. Some results indicate that the receptor is present in M-cones of the adult rat retina. The aim of the study was to examine whether cones express TrkB receptor during development and to test if BDNF and NT-4 are involved in cone differentiation.
Retinas of Sprague-Dawley rats were collected in different developmental ages and analyzed by immunocytochemistry using cone- and TrkB-specific antibodies. For the functional studies, organotypic retina cultures allowing M-cone development were prepared from P2 rats. In order to neutralize the endogenous neurotrophins acting via the TrkB receptor, cultures were treated with BDNF- or NT-4-specific antibodies continuously for 19 days. The cultures were then processed histologically, and the M-cone densities of treated and non-treated control retinas have been compared.
The first M-opsin positive signals were detected at P10 in dual cones expressing both the S- and M-opsin. The expression of TrkB receptor started at P10, at the same time when the M-opsin appeared. In contrast to the adult, in which only the mature M-cones expressed the receptor, in the developing retinas TrkB receptor expression was detected in every cone that expressed M-opsin. Although the majority of S-opsin positive cells were colocalized with the TrkB receptor during development, some cones showed single S-opsin expression. The overall retinal architecture was well preserved both in control and anti-NT-4 treated cultures. Every retinal layer was well developed and no major differences were found. Although the photoreceptor layer was comparable to that of the control and anti-NT-4 treated retinas, anti-BDNF treatment resulted in a remarkable thinning of the inner retina. The average M-cone density in the control cultures was ~4450 ±870 cell/mm3. Neither the anti-BDNF nor the anti-NT-4 treatment effected M-cone density; similar values with no significant differences were calculated in both treated groups.
The TrkB receptor is expressed in the developing, and later, in the mature M-cones as well. Our results indicate that neurotrophins may be involved in M-cone development and function, however, their role in the regulation of M-opsin expression is unlikely.
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