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NL Ransom, NG Tahzib, HA Reitsamer, SJ McKinnon; TrkB Expression in Photoreceptor Mitochondria in Normal Baboon Retinas . Invest. Ophthalmol. Vis. Sci. 2002;43(13):734.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Brain derived neurotrophic factor (BDNF) has been shown to rescue photoreceptors in animal models of retinal degeneration. The purpose of the present study was to determine the distribution of the high affinity BDNF receptor tyrosine kinase trkB in normal baboon retina. Methods: An adult baboon eye was enucleated and fixed with 4% paraformaldehyde and 0.1% gluteraldehyde in 0.1M PO4, pH 7.4, for 1 hour. After fixation the retina with attached pigment epithelium was embedded in LR Gold resin (Polysciences, Inc. Warrington, PA) at 4°C. Ultra-thin sections were labeled with three separate antibodies. Two polyclonal antibodies specifically recognize trkB (goat anti-trkB, Santa Cruz, Burlingame, CA; rabbit anti-trkB, gift of David Kaplan, Univ. of Montreal) and one mouse monoclonal recognizes all trk isoforms (Zymed, San Francisco, CA). Sections were imaged on Philips transmission electron microscopes. Controls included blocking peptide (Santa Cruz antibody), rabbit pre-immune serum (Kaplan antibody), no primary antibody and species-specific IgG . Results: Immunocytochemical labeling of baboon photoreceptors with two separate anti-trkB-specific antibodies showed expression localized to inner segment mitochondria and cytosol. Labeling was also seen in the nerve fiber layer, ganglion cells, Müller cells, and the cytoplasm of inner and outer nuclear layers. There was no difference in expression patterns between cones and rods. The mouse monoclonal pan-trkB antibody displayed a similar expression pattern. All control sections showed negligible labeling. Conclusions: TrkB appears to be robustly expressed in inner segment mitochondria of baboon cone and rod photoreceptors. Although in previous studies trkB activity has not been demonstrated in photoreceptors, our findings suggest a possible functional or storage role of trkB in primate rods and cones.
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