Localization of NMDA receptor subunits and mapping NMDA drive within the mammalian retina

Abstract

Glutamate is a major neurotransmitter in the retina and other parts of the central nervous system, exerting its influence through ionotropic and metabotropic receptors. One ionotropic receptor, the N-methyl-D-aspartate(NMDA) receptor, is central to neural shaping, but also plays a major role during neuronal development and in disease processes. We studied the distribution pattern of different subunits of the NMDA receptor within the rat retina including quantifying the pattern of labelling for all the NRI splice variants, the NR2A and NR2B subunits. The labelling pattern for the subunits was confined predominantly in the outer two-thirds of the inner plexiform layer. We also wanted to probe NMDA receptor function using an organic cation, agmatine (AGB); a marker for cation channel activity. Although there was an NMDA concentration-dependent increase in AGB labelling of amacrine cells and ganglion cells, we found no evidence of functional NMDA receptors on horizontal cells in the peripheral rabbit retina, nor in the visual streak where the type A horizontal cell was identified by GABA labelling. Basal AGB labelling within depolarizing bipolar cells was also noted. This basal bipolar cell AGB labelling was not modulated by NMDA and was completely abolished by the use of L-2-amino-4-phosphono-butyric acid,which is known to hyperpolarize retinal depolarizing bipolar cells. AGB is therefore not only useful as a probe of ligand-gated drive, but can also identify neurons that have constitutively open cationic channels. In combination,the NMDA receptor subunit distribution pattern and the AGB gating experiments strongly suggests that this ionotropic glutamate receptor is functional in the cone-driven pathway of the inner retina.

Distinct perisynaptic and synaptic localization of NMDA and AMPA receptors on ganglion cells in rat retina

“…IR at the LM level was similar to previous reports in rat retina (Fletcher et al, 2000;Kalloniatis et al, 2004). Intense, punctate labeling was evident in the IPL and OPL, in addition to somatic labeling in the GCL and INL ( Figure 3A, C).…”

Functional and neurochemical development in the normal and degenerating mouse retina

“…All amino acid antibodies were tested for crossreactivity by dot immunoassays (Marc et al, 1990(Marc et al, , 2005Marc, 1999) and demonstrate specificity for the relevant amino acid coupled antigen (Signature Immunologics data sheets at http://www.immunologics.com/ products.html: L-glutamate E100; glycine G100; L-glutamine Q100; GABA YY100: the relevant Millipore Chemicon and Abcam data sheets contain similar data). Amino acid antibodies have been used in numerous other retinal studies and show an identical labeling pattern (Marc et al, 1990(Marc et al, , 1995(Marc et al, , 2007Kalloniatis and Fletcher, 1993;Marc, 1999;Marc and Jones, 2002;Kalloniatis et al, 2002Kalloniatis et al, , 2004. There was no measurable glutaraldehydefixed tissue crossreactivity against the other amino acids used in this study.…”

Disinhibition Combines with Excitation to Extend the Operating Range of the OFF Visual Pathway in Daylight

“…Virtually every circuit, from photoreceptors to amacrine or ganglion cells in the inner retina, requires at least one synapse mediated by an iGluR (Marc, 1999a,b;Kalloniatis et al, 2004;Dumitrescu et al, 2006). The one known exception is the following circuit: cone 3 ON cone bipolar cell 3 AII amacrine cell 3 OFF ganglion cell (see Introduction); rods could also drive this circuit through their gap junctions with cones.…”