Region-specific decline in the expression of metabotropic glutamate receptor 7 mRNA in rat brain during aging

Age-dependent changes in the expression of group III metabotropic glutamate receptors (mGluR4 and mGluR7) were studied by quantitative in situ hybridi zation using male Fisher 344 rats 3, 12 and 25 months of age. Results indic ate an early decrease in mGluR7 mRNA level in several cortical areas includ ing the frontal, parietal and temporal cortices. In the hippocampus, mGluR7 mRNA levels decreased in the CA1 region and the lower blade of the dentate gyrus. Moreover, significant decrease was found in the laterodorsal thalam ic nucleus at 12 months of age. Other regions such as the caudate putamen a nd nucleus accumbens showed no age-related changes in mGluR7 mRNA levels. A nalysis of emulsion autoradiograms revealed a 36% decrease of mGluR7 mRNA i n Purkinje neurons in the 12-month-old group and a 48% decline in the 25-mo nth-old group as compared to the 3-month-old group. A substantial decrease in mGluR4 mRNA level was found in the granule cell layer of the cerebellum during aging. The difference between the young and aged groups exceeded 35% . These region-specific decreases may have important implication in some of the age-related changes in cognitive, motor and/or sensory functions. (C) 2000 Elsevier Science B.V. All rights reserved.