Expression of the mRNA of Seven Metabotropic Glutamate Receptors (mGluR1 to 7) in the Rat Retina. An In Situ Hybridization Study on Tissue Sections and Isolated Cells

Abstract

We have studied the expression of mRNAs for seven metabotropic glutamate receptors (mGluR1-7) in the retina of the adult rat by in situ hybridization with tissue sections and isolated cells using [alpha 35S]dATP-labelled oligonucleotide probes. Hybridization revealed the expression of six of the metabotropic receptor mRNAs, mGluR1, 2 and 4-7, in the retina, while mGluR3 was not detected. Each of the expressed receptor mRNAs showed a distinct pattern of expression. In the outer nuclear layer, corresponding to photoreceptor somata, no labelling was detected. In the outer part of the inner nuclear layer, putative horizontal cells were labelled for mGluR5. More proximal in this layer, corresponding to the position of bipolar cell somata, there was strong labelling for mGluR6. A small number of bipolar cells were also labelled for mGluR5 and mGluR7. In situ hybridization with isolated cells showed that mGluR6 was expressed by rod bipolar cells. Subsets of amacrine cells, with cell bodies along the border between the inner nuclear layer and the inner plexiform layer, were positive for mGluR1, 2, 4 and 7, suggesting considerable heterogeneity of these receptors among amacrine cells. None of the seven metabotropic receptor mRNAs was expressed in isolated Müller glial cells. In the ganglion cell layer, virtually every ganglion cell and displaced amacrine cell was labelled for mGluR1 and mGluR4. Some cells in this layer (approximately 20% of the total), most likely both ganglion cells and displaced amacrine cells, were also labelled for mGluR2 and mGluR7. These findings suggest that metabotropic glutamate receptors are considerably more widespread among neurons in the retina than indicated by previous physiological and pharmacological investigations.

Phylogeny and expression divergence of metabotropic glutamate receptor genes in the brain of zebrafish (Danio rerio)

“…However, as mGluR3 is -in contrast to our data -not (Joselevitch et al, 2007;Cai and Pourcho, 1999), and as we could not find mglur2b-positive labeling in the larval fish retina, this function seems to be exclusively mediated by zebrafish mGluR2a. In addition, the expression of mglur2 mRNA in rat amacrine and ganglion cells (Hartveit et al, 1995) agrees well with the expression of mglur2a in the proximal INL and GCL.…”

“…Other interesting differences in expression exist for the mglur6 paralogs: Vertebrate mGluR6 is known to be involved in the ON-bipolar cell signaling being exclusively expressed in ON-bipolar cell dendrites (Hartveit et al, 1995;Masu et al, 1995;Nomura et al, 1994;Ueda et al, 1997;Vardi et al, 2000;Vardi and Morigiwa, 1997). We only found expression of mglur6b in the medial INL, where bipolar cell bodies are located, whereas mglur6a is not expressed in this layer at larval stages.…”

Immunohistological Studies of Metabotropic Glutamate Receptor Subtype 6-Deficient Mice Show No Abnormality of Retinal Cell Organization and Ganglion Cell Maturation

“…Of eight different mGluR subtypes known presently, all but mGluR3 have been shown to be expressed and distinctly localized in different cell types of the rat retina (Shigemoto et al, 1992;Nakajima et al, 1993;Ohishi et al, 1993;Akazawa et al, 1994;Nomura et al, 1994;Duvoisin et al, 1995;Hartveit et al, 1995;Brandstätter et al, 1996;Koulen et al, 1996Koulen et al, , 1997. It has been reported that ablation of a specific gene alters expression patterns of closely related genes (Hummler et al, 1994;Blendy et al, 1996).…”

Optic nerve and neuroprotection strategies

“…23 This is explained by the fact that ionotropic glutamate receptors are primarily associated with ganglion cells and subsets of amacrine cells. 24 Role of toxic mediators in ganglion cell death Present evidence suggests that retinal astrocytes and microglia may become activated as a result of optic nerve injury and ischaemia, and can release toxic substances (eg glutamate, D-serine, nitric oxide, tumour necrosis factors a and b) into the extracellular space. These factors may contribute to the damage in ganglion cells.…”