Abstract
The ubiquitous distribution of the classic endocannabinoid system (cannabinoid receptors CB1 and CB2) has been demonstrated within the monkey nervous system, including the retina. Transient receptor potential vanilloid type 1 (TRPV1) is a cannabinoid-like non-selective cation channel receptor that is present in the retina and binds to endovannilloids and endocannabinoids, like anandamide, 2-arachidonoylglycerol and N-arachidonoyl dopamine. Retinal expression patterns of TRPV1 are available for rodents and data in higher mammals like humans and monkeys are scarce. We therefore thoroughly examined the expression and localization of TRPV1 in the retina, at various eccentricities, of the vervet (Chlorocebus sabeus) monkey, using Western blots and immunohistochemistry. Our results demonstrate that TRPV1 is found mainly in the outer and inner plexiform layers, and in the retinal ganglion cell (RGC) layer with a higher density in the periphery. Co-immunolabeling of TRPV1 with parvalbumin, a primate horizontal cell marker, revealed a clear overlap of expression throughout the entire cell structure with most prominent staining in the cell body membrane and synaptic terminals. Furthermore, double labeling of TRPV1 and syntaxin was found throughout amacrine cells in the inner plexiform layer. Finally, double staining of TRPV1 and Brn3a allowed us to confirm its previously reported expression in the cell bodies and dendrites of RGCs. The presence of TRPV1 in the horizontal pathway suggests a function of this receptor in lateral inhibition between photoreceptors through the horizontal cells, and between bipolar cells through amacrine cells.
Highlights
The ubiquitous distribution of the classic endocannabinoid system has been demonstrated within the monkey nervous system, including the retina
Our results demonstrated that TRPV1 was mainly expressed in the horizontal system of the retina that adds to the previously reported data by our laboratory on the endocannabinoid receptor expression in the vertical retinal system
We propose a model regarding the putative role of TRPV1 in a two-stage lateral inhibition, one at the receptor level through horizontal cells and the other at the bipolar cells’ level through amacrine cells, that might contribute to perceptual contrast enhancement
Summary
The ubiquitous distribution of the classic endocannabinoid system (cannabinoid receptors CB1 and CB2) has been demonstrated within the monkey nervous system, including the retina. As for the primate retina, only one study has located TRPV1 receptor in the GCL, but the exact retinal locus was not reported, neither the complete specific retinal cell types expressing it. This receptor was found in the RGC dendrites, with diffuse labeling in the soma. Our results demonstrated that TRPV1 was mainly expressed in the horizontal system of the retina (horizontal and amacrine cells) that adds to the previously reported data by our laboratory on the endocannabinoid receptor expression in the vertical retinal system (from photoreceptors to ganglion cells). We propose a model regarding the putative role of TRPV1 in a two-stage lateral inhibition, one at the receptor level through horizontal cells and the other at the bipolar cells’ level through amacrine cells, that might contribute to perceptual contrast enhancement
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