Coexpression patterns of mGLuR mRNAs in rat retinal ganglion cells: a single-cell RT-PCR study

Eight different subunits of metabotropic glutamate receptors (mGluRs) are known to date. mGluRs have been linked to an extensive list of neuromodulatory effects, depending on which intracellular or membrane-bound effector system is activated. Activation of mGluRs can influence neuronal activity and can result in changes of intracellular Ca2+ homeostasis-that is, changes in factors that are known to be crucial for cellular differentiation and cell death. Because mGluRs are known in modulating both intracellular and intercellular activities, this study was designed to determine which types of mGluRs are coexpressed in a neuron and whether distinct coexpression patterns can be found that reflect the different physiological requirements of a neuron at different stages of development and to learn whether neuronal injury results in adaptive changes of mGluR expression.

Juvenile and adult rat retinal ganglion cells (RGCs) and adult RGCs after axotomy were analyzed for their gene expression pattern of mGluRs by single-cell reverse transcription-polymerase chain reaction (RT-PCR).

Adult RGCs predominantly expressed one or two different mGluR mRNAs, whereas juvenile RGCs coexpressed two and more. mGluR3, -5, and -7 mRNAs were found more frequently in juvenile than in adult RGCs. mGluR6 was detected in juvenile RGCs in low abundance but never in adult RGCs. However, mGluR6 was expressed in adult RGCs after axotomy. mGluR1 and -7 were also found more frequently in axotomized RGCs than in the adult control group.

All types of mGluR mRNAs are expressed in RGCs. This is in contrast with previous in situ hybridization and immunohistochemical studies in which expression of mGluR3, -5, and -6 was not reported. The expression of some mGluR mRNAs seems to be developmental, although no distinct copatterns were found.