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J.H. Brandstatter, H. Wegmeyer, K. Reim, N. Brose; Synapse-Specific Expression of Complexins in the Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1063.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Complexins are a family of small, soluble proteins that bind to the assembled exocytotic core complex, and are involved in the regulated release of neurotransmitter at synapses. To date, four Complexins are known, Complexin I to IV (CPX I to IV). We examined whether different types of chemical synapses in the retina, glutamatergic, glycinergic and GABAergic, express different Complexins. Methods: Using single and double-labeling immunocytochemistry and confocal laser scanning microscopy, we analysed the cellular and synaptic expression of CPX I to CPX IV in the mouse retina. Results: CPX I/II: labeling is found in the inner plexiform layer (IPL) with several strata of higher and lower immunoreactivity. In addition, CPX I/II is found in horizontal cell processes in the outer plexiform layer (OPL) and in somata of amacrine and ganglion cells in the inner nuclear layer (INL) and the ganglion cell layer. Double-labeling experiments suggest a selective expression of CPX I/II at GABAergic synapses and an absence at glutamatergic synapses. CPX III: labeling is found in both synaptic layers of the retina and in the INL. In the OPL, the glutamatergic terminals of rods and cones, and in the IPL the glutamatergic terminals of bipolar cells and the processes of amacrine cells stain for CPX III. Mainly glycinergic amacrine cells express CPX III at their synapses. CPX IV: of the four Complexins, CPX IV is found only in the retina and nowhere else in the brain. Furthermore, CPX IV is expressed at glutamatergic synapses only. In the OPL, CPX IV is present in the synaptic terminals of rods but not cones, and in the IPL it is found in the terminals of a subpopulation of ON-cone bipolar cells. Conclusions: All four known Complexins are present in the retina, and they are selectively expressed among the glutamatergic, glycinergic and GABAergic synapses. The differential and synapse-specific expression of the Complexins is likely to reflect differences in the presynaptic molecular machinery, responsible for the different modes of neurotransmitter release found at retinal synapses.
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