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S. Yazulla, S. Zimov; Fatty Acid Amide Hydrolase (FAAH) and Vanilloid Receptor 1 (TRPV1/VR1) Colocalization in Goldfish Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5960.
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© ARVO (1962-2015); The Authors (2016-present)
The lipophilic endocannabinoid, anandamide (AEA) but not 2-arachydonoyl glycerol (2-AG), is an endogenous ligand for both the metabotropic cannabinoid (CB1) and ionotropic TRPV1 receptors. The major hydrolyzing enzyme for AEA metabolism is fatty acid amide hydrolase (FAAH). Previous work in this lab has established the presence and function of the endocannabinoid system in rat and goldfish retina. The relationship between TRPV1 and the endocannabinoids is of great interest regarding nociception and inflammatory responses. Despite extensive data in the CNS, far less is known about TRPV1 in the retina.
Goldfish retinas were fixed in 4% paraformaldehyde and incubated in combinations of primary antibodies: rabbit anti-FAAH or anti-GAD67, guinea pig anti-TRPV1, rat anti-SubP, mouse anti-SRIF. Also, goldfish eyes were removed and crystals of tetramethylrhodamine dextran were placed on the cut optic nerve. Whole eyes were incubated in an excess of a HEPES-buffered DMEM/F12 culture media for 4-6 days at 10°C. Retinas were fixed in 4% paraformaldehyde and processed as above for immunocytochemistry using a rabbit polyclonal anti-rhodamine. LM immunohistofluorescence was used to localize immunoreactivity (IR).
TRPV1-IR labeled a subpopulation of FAAH-IR cells and processes in the inner plexiform layer of goldfish retina. These cells were rare and constituted subpopulations of amacrine cells and ganglion cells including ovoid, pyriform, and giant amacrine cells and giant ganglion cells. The giant amacrine cells had large caliber dendrites that were diffusely stratified in the IPL. These appear to correspond to large ON-OFF 'fnd' cells reported by Teranishi et al '85,87). The giant ganglion cells had their major projection to the distal IPL and are similar to the giant OFF Type 1 alpha ganglion cells (Kock & Reuter, '78; Vallerga & Djamgoz, '91). TRPV1-IR amacrine cells were not labeled with somatostatin or substance P. Large pyriform amacrine cells labeled with GAD-IR and constituted a subpopulation of GABAergic amacrine cells. The giant TRPV1/FAAH amacrine cells appeared to constitute a separate neurochemical class, which was neither GABAergic nor glycinergic.
The presence of TRPV1 and FAAH in the same neurons is indicative of an autoregulatory function for anandamide. Due to the rarity of these cells, the TRPV1 vanilloid amacrine cells may participate with endocannabinoids and CB1 receptors in the modulation of wide field effects, for example, sampling of ambient light conditions and maintaining retinal sensitivity.
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