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Maria M. Aldape, Magaly M. Escamilla, Jorge A. Perez-Leon; Iprgc Expressing Gaba, Glycine And Glutamate Receptors. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4351.
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© ARVO (1962-2015); The Authors (2016-present)
IpRGCs are the photoreceptor most recently described in vertebrate retina and unlike to rods and cones, ipRGC's express the opsin melanopsin (OPN4). These cells project at the suprachiasmatic and the olivary pretectal nuclei, therefore are implicated in circadian photoentrainment and pupillar responses to light. These functions, make them different from the other types of retinal ganglion cells (RGC), suggest that their neurotransmitter receptor set can be distinct from the rest of the RGC. Because the intraretinal synaptic network of the ipRGCs are not completely clear we aimed to determine the neurotransmitter receptors present on these cells.
We performed immunfluorescence studies on localized ipRGCs in rat retina. Double labeling experiments using a polyclonal rabbit antibody directed to OPN4 with antibodies recognizing several neurotransmitter receptors and synaptic proteins were done in vertical sections from the retinae of rats aged 2-2 1/2 months. The standard double labeling technique was used, however was modified for the use of two primary antibodies raised in rabbit. The slides were analysed by normal epifluorescence microscopy.
OPN4 cells were found with features alike to those already described in rat and mouse retinae. Nonetheless, we also found a scarce but consistent labeling for OPN4 in cells allocated at the inner nuclear layer, these cells were positive for calretinin. The synaptic proteins PSD95 and the vesicular Glutamate transporter 2 were not found on OPN4 cells. The vesicular acetylcholine transporter and the gephyrin antibodies did not labeled the cells positive for OPN4. We never found colocalization of OPN4 signal with that of the rod bipolar cell marker PKC.An antibody recognizing the AMPA receptor subunits 2,3 labeled the OPN4 cells, whereas an antibody directed to the NMDAr1 did not. The α1 GABAa receptor subunit was found in all the OPN4 cells, in the somata and the dendritic processes. The pan antibody to the postsynaptic glycine receptor labeled some of the OPN4 cells, and the α1 GlyR did not colocalize.
Our data show that the ipRGC express a restricted set of neurotransmitter receptors and synapse associated proteins. This could be related to their low spontaneous synaptic activity. Also, it looks that OPN4 is present on some other retinal neurons aside the RGC.
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