Developmental profile of metabotropic glutamate receptor mRNA in rat brain

We have studied the expression of metabotropic glutamate receptor (mGluR) mRNA by Northern blot analysis with a specific cDNA probe (the pmGR1 probe). In 1-day-old rats, the steady state levels of mRNA were higher in the hypothalamus and olfactory bulb, with intermediate levels in the cerebellum and low levels in the hippocampus and cerebral cortex. In the olfactory bulb, hypothalamus, and cerebral cortex, the expression of mGluR mRNA remained constant at 8 and 30 days of postnatal life. In contrast, in the cerebellum and hippocampus, mRNA levels increased progressively with age. There was no correlation between levels of mGluR mRNA and stimulation of polyphosphoinositide hydrolysis by 1-aminocyclopentane-1S,3R-dicarboxylic acid (trans-ACPD), which was much greater in brain slices from 8-day-old rats and was nearly absent in the adult cerebellum and olfactory bulb, where we have found the highest levels of mRNA. In addition, mGluR mRNA was detectable in cultured cerebellar granule cells but not in cultured neurons from cerebral hemispheres or in cultured astrocytes, which responded to trans-ACPD with an increased formation of [³H]inositol monophosphate. The discrepancies between levels of mGluR mRNA detected with the pmGR1 probe and trans-ACPD-stimulated polyphosphoinositide hydrolysis suggest either that different subtypes of mGluRs exist or that mRNA levels are not critical for the dynamic changes in the activity of mGluRs during development.