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S Zimov, S Yazulla; Immunolocalization of the Vanilloid (Capsaicin) Receptor 1 Polyclonal Antibody in the Goldfish Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3760.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The Vanilloid (Capsaicin) receptor (VR1) is present in the brain and has homology to the Drosophila retinal transient release potential (TRP) protein (Mezey et al., '00; Caterina et al., '97). Endogenous cannabinoids stimulate metabotropic CB1 receptors and possibly ionotropic VR1 receptors. As CB1 receptor localization and function have been reported in goldfish cones, we examined the localization of the VR1 antibody in relation to antibodies with known anatomical distributions in the outer retina. Methods: Goldfish retinas were fixed in 4% paraformaldehyde and incubated in a guinea pig polyclonal anti-VR1 and one of the following antibodies: rabbit polyclonal anti-CB1, anti-GLUR4, anti-GABAAα3, mouse monoclonal anti-GLUR2, anti-PKC or anti-ZPR1. LM immunohistofluorescence was used to localize immunoreactivity (IR). Results: VR1-IR was restricted to the OPL and gave the appearance of a medium caliber dendrite sectioned in different plains; there was no evidence for somatic staining. VR1-IR was associated with cones, but not rods; it was located at the base of double cone terminals, as visualized with ZPR1-IR, and appeared to be within the pedicle complex. Glur2-IR, which labels the tips of cone horizontal cell dendrites, was distal to the VR1-IR regions. However, Glur4-IR, which labels OFF bipolar cell dendrites, was just proximal to the VR1-IR regions. VR1-IR was in the same layer as the ON and OFF mixed rod/cone and cone bipolar cell dendrites, as visualized by PKC-IR and GABAAα3-IR, respectively. VR1-IR appeared interspersed among these bipolar cell processes, but did not co-localize with them. Finally, CBR1-IR, which was localized to the membrane of cone pedicles, was in the same region as VR1-IR and also appeared to be interspersed with VR1-IR. Conclusion: VR1-IR labels a structure in the goldfish OPL with a novel immunocytochemical signature. Based on exclusion with double labels, we suggest that VR1-IR labels dendrites of the cone horizontal cells at the base of and within the cone pedicle, but distant from the ribbon, unlike Glur2-IR that labels the dendritic tips. Endocannabinoids may exert both pre and postsynaptic modulation in the outer retina.
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