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S. Yazulla, K.M. Studholme; Novel Neurons in Rat and Monkey Retina Stained by Antibodies Against the Vanilloid Receptor-Like Protein: Cajal's Centrifugal Bipolar Cell? . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4135.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Endocannabinoids are ligands for cannabinoid CB1 and vanilloid receptors. As CB1 receptors are present in mammalian retinas (Straiker et al, 1999; Yazulla et al., 1999), we investigated the distribution of vanilloid receptor 1 (VR1) and vanilloid receptor like-1 (VRL1) antigens in rat and macaque retinas. VR1 and VRL1 form ligand-gated non-selective cation channels with high Ca2+ permiability. Methods: Standard LM immunofluorescence on cryostat sections of rat and macaque retinas was performed with anti-VR1 and anti-VRL1. Double labelings with anti-TOH, GAD, PKC and synaptic vesicle protein 2 (SV2) were performed to identify the immunoreactive (IR) structures. Results: No labeling was observed with anti-VR1 in rat or human retinas. However, two similar cell populations were VRL1-IR in the rat and monkey retinas. The major difference was the near lack of VRL1-IR somas in monkey. The first type was characterized by a thin process that extended from the INL to the OPL to end in a loose tuft that were clustered sporadically and did not form a continuous layer in the OPL. The appearance was similar to isolated tree roses, hence our term, arbor rosa cells. VRL1-IR did not co-localize with PKC-IR, TOH-IR or GAD-IR, demonstrating that these were not dopamine or GABA interplexiform cells (IPC). The only structures that appear to resemble VRL1-IR cells are the centrifugal bipolar cells described by Cajal in dog and Polyak in primate. The second cell type, in rat only, was a large, rare amacrine cell with processes in layer 1 of the IPL and lighter label in layers 3 and 5. VRL1-IR and TOR-IR boutons encircled and intertwined around the same amacrine cell bodies but did not co-localize. The same relation was observed with VRL1-IR and TOH-IR processes in monkey retina. VRL1-IR processes in transit through the INL were not SV2-IR, while those surrounding amacrine cell bodies were. Conclusions: VRL1-IR processes, along with dopaminergic cells, form a complimentary plexus of axosomatic contacts on a subpopulation of amacrine cells. VRL1-IR arbor rosa cells are not dopamine- or GABA-IPCs but may be the first non-Golgi description of centrifugal bipolar cells described by Cajal in the dog retina and Polyak in the macaque. The narrow projection and scattered distribution of processes in the OPL suggests a modulatory, paracrine function rather than a role in precise visual coding for the arbor rosa cells. The function of VRL1 channel proteins in these retinal cells is not clear. A mouse orthologue of VRL1 is regulated by insulin-like growth factor 1, hinting at a special role for these neurons in cell signalling.
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