Fig 1: Schematic illustration of the hypothetical mechanism of action of TRPV1 in horizontal cells of the monkey retina following stimulation of a cone. The different steps are highlighted by numbers. (1) When a cone is stimulated (C1), endocannabinoids (eCBs), particularly AEA and 2-AG, are produced in the synaptic cleft. (2) TRPV1 receptors are activated by eCBs in horizontal cells. (3) The calcium influx through the membrane causes depolarization of the horizontal cell. (4) GABA release in the synaptic cleft. (5) GABA binds to GABA receptors on the presynaptic neighboring cone pedicle (5). This mechanism of lateral inhibition could also potentially modulate the information transmitted to the bipolar cells and retinal ganglion cells. S spot stimulus, C1 stimulated cone 1, C2 adjacent cone 2, H horizontal cell, eCB endocannabinoid, GABAr Gamma-amino-butyric acid receptors, TRPV1 Transient receptor potential vanilloid type 1.
Fig 2: Characterization of the TRPV1 antibody in the monkey retina. Western blot analysis of total protein samples from a vervet monkey retina, showing detection of the expected protein band at 100 kDa (A). The band was not detected when the antibody was pre-incubated with its corresponding TRPV1 blocking peptide (BP) at the ratio 1:10 (A). All lanes contained 10 μg of total protein. Immunohistochemistry on vervet retinal tissue with the antibody raised against TRPV1 revealed a unique staining profile (B). When the TRPV1 antibody was pre-incubated with its corresponding BP, it revealed an absence of staining in the vervet retinas (C). Quantitative analysis of the TRPV1 fluorescent signal through the six different retinal layers reveals a relatively higher signal intensity in the OPL and the GCL layers compared to the photoreceptor (PRL) and the outer nuclear (ONL) layers (P < 0.05) (D). TRPV1 transient receptor potential vanilloid type 1, BP blocking peptide, LC loading control, PRL photoreceptor layer, ONL outer nuclear layer, OPL outer plexiform layer, INL inner nuclear layer, IPL inner plexiform layer, GCL ganglion cell layer. Scale bar = 75 μm. Mean optical density ratios ± standard error of the mean (SEM) are depicted.
Fig 3: Double-label immunofluorescence showing no signal for TRPV1 in rod bipolar cells and Müller cells. TRPV1 is neither expressed in the cell bodies (small arrows in the upper INL) of bipolar cells nor their synaptic terminals at the edge of the OPL (arrowheads). Each protein expression is presented alone in grayscale: PKC (A) and TRPV1 (B); then, the two are presented merged (C), PKC in green and TRPV1 in red. Long arrows show specifically that the Müller cell bodies do not express TRPV1. Each protein expression is presented alone in grayscale: glutamine synthetase (D) and TRPV1 (E); then, the two are presented merged (F), glutamine synthetase in green and TRPV1 in red. Scale = 75 µm for (A–F).
Fig 4: Double-label immunofluorescence illustrating immunolabeling of TRPV1 in ganglion cells, horizontal cells, and amacrine cells. (A-C) The antibody against Brn3a labels the nucleus of ganglion cells in the monkey retina, and these cells were strongly TRPV1 immunoreactive. Arrows indicate Brn3a-positive ganglion cells that are TRPV1 immunoreactive. Each protein expression is presented alone in grayscale: Brn3a (A) and TRPV1 (B); then, the two are presented merged (C), Brn3a in green and TRPV1 in red). (D-I) TRPV1 is expressed in horizontal cell synaptic terminals (arrows in OPL) and cell bodies (arrowheads in the INL). Each expression is presented alone in grayscale: PV (D,G), TRPV1 (E,H); then, the two are presented merged (F,J). (J–L) Arrows show the expression of TRPV1 in the amacrine cell bodies (INL). Each expression is presented alone in grayscale: syntaxin-positive amacrine cells (J) and TRPV1 (K); then, the two are presented merged (L). INL inner nuclear layer, IPL inner plexiform layer, OPL outer plexiform layer, GCL ganglion cell layer. Scale = 75 µm for (A–C) and (J–L), 30 µm for (D–F) and 10 µm for (G–I).
Fig 5: Mapping of the receptors CB1R, CB2R, GPR55, and TRPV1 in the monkey retina. These receptors are differently expressed in the retina of monkeys. These results are compiled from several published articles26,31,35. CB1R is represented in green, CB2R in magenta, GPR55 in blue, and TRPV1 in red. OS, photoreceptors outer segments; IS, photoreceptors inner segments; ONL, outer nuclear layer; ONL, outer plexiform layer; INL, inner nuclear layer; IPL, inner plexiform layer; GCL, ganglion cell layer.
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