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H Wassle, S Haverkamp, EL Fletcher, U Grünert; Synaptic Distribution of Ionotropic Glutamate Receptors in the Inner Plexiform Layer of the Primate Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):892.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The synaptic transmission from bipolar cells onto amacrine and ganglion cells is mediated by glutamate. Depending on the type of glutamate receptor (GluR) expressed, the light responses of the postsynaptic cells differ. The synaptic distribution of ionotropic GluR subunits was studied in the inner plexiform layer (IPL) of the primate retina. Methods: Shortly fixed tissue (2% paraformaldehyde, 15-30 min) was processed for immunofluorescence double-labeling and preembedding electron microscopy using antibodies against the GluR1, GluR2, GluR2/3, GluR4, NR1C2', NR2A, GluR6/7 and Delta1/2 subunits. Results: A punctate immunofluorescence pattern was observed in the IPL for all subunits tested, and electron microscopy confirmed that the immunoreactive puncta represent clustering of the GluRs at sites postsynaptic to bipolar cell ribbon synapses (dyads). Usually only one of the two postsynaptic processes at the dyads expressed a given subunit. Immunoreactive GluR2, GluR2/3 and GluR4 puncta were found at high density throughout the IPL and are probably expressed at every dyad. The GluR1 subunit was expressed at lower density. The N-methyl-D-aspartate (NMDA) receptor subunits NR2A and NR1C2' were restricted to synapses localized in two broad bands in the center of the IPL. They were often colocalized with GluR2/3 and GluR4 subunits. The orphan receptor subunits Delta1/2 predominated in three horizontal bands. The kainate receptor subunits GluR6/7 were clustered in large postsynaptic densities adjacent to bipolar cell axon terminals, but lacking a synaptic ribbon on the presynaptic side. This might represent a conventional synapse made by a bipolar axon terminal. Conclusion: GluR2/3 and GluR4, together with NMDA receptors, are preferentially expressed on ganglion cell dendrites, while kainate receptors and the Delta1/2 subunits are mostly localized on amacrine cell processes.
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