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T. Puthussery, L. Foster, E.L. Fletcher; Synaptic Localisation of P2X7 Receptors in the Mammalian Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5167.
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Purpose: The extracellular purine, adenosine 5’triphophate (ATP) is known to mediate neurotransmission and neuromodulation in various parts of the central nervous system. There are two major receptor classes that are sensitive to extracellular ATP; the ionotropic P2X receptors (P2X1-7) and the metabotropic P2Y receptors (P2Y1-11). The aim of this study was to examine the localisation of the homomeric P2X7 receptor subunit in the retina. Methods: Retinae of adult white rabbits and adult Spraque Dawley rats were lightly fixed and processed for indirect immunofluorescence immunocytochemistry and preembedding immunoelectron microscopy. Sections were immunolabelled with an anti-P2X7 antibody (Chemicon) and double labelled with various cell markers including protein kinase C (PKC), Calbindin (CalB) and post synaptic density protein 95 (PSD-95). Results:Light microscopical analysis revealed punctate immunolabelling of the P2X7 subunit in the plexiform layers, indicative of synaptic clustering. In the rat retina, outer plexiform layer puncta were colocalised with CalB positive horizontal cells. In the inner plexiform layer of both the rat and rabbit, a diffuse punctate pattern of labelling was observed. Puncta localised to the "ON" sublamina of the inner plexiform layer were colocalised with the rod bipolar cell marker, PKC. Interestingly, no immunolabelling of Müller cells with P2X7 was observed. Ultrastructural investigation confirmed the presence of the P2X7 subunit on horizontal cell terminals and also revealed P2X7 subunit labelling presynaptically at the rod photoreceptor ribbon synapse. Amacrine cells postsynaptic to the rod bipolar cell terminal were also P2X7 immunoreactive. Conclusions: This data suggests that postsynaptic P2X7 receptors may be involved in signal transmission in the rod pathway as well as in modulation of horizontal cell signalling. In addition, presynaptic P2X7 receptors may influence rod photoreceptor signalling.
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