Influence of environmental enrichment on steady-state mRNA levels for EAAC1, AMPA1 and NMDA2A receptor subunits in rat hippocampus.

Interaction with the environment has a key role in refining the neuronal circuitry required for normal brain function throughout life. Profound effects of enriched environment have been shown on neuronal structure and chemistry in experimental animals. Epidemiological studies imply that this is true also in man, thus cognitive stimulation has a protective effect on neurodegeneration, e.g., in Alzheimer's disease. Glutamatergic pathways are imperative for cognitive functions, such as memory, learning and long-term potentiation, and relies on the AMPA and NMDA glutamate receptors and the hippocampus, with its specific subregions, is an important anatomical substrate in this. The glutamate signalling is also dependent on a fine-tuned transport system, in the hippocampus primarily achieved by the glutamate transporter EAAC1. In this study we show how environmental enrichment modulates these parts of the glutamatergic system using quantitative in situ hybridisation. This work demonstrates for the first time that environmental enrichment modulates the mRNA expression of EAAC1 which is significantly and region specifically decreased in the hippocampus. We also provide evidence for regional and hemisphere-specific upregulation of NMDA mRNA in the hippocampus after environmental enrichment. The current work also shows that AMPA mRNA of the hippocampus is not per se changed by environmental enrichment in adult animals. Taken together, our results extend the knowledge of the glutamatergic system of specific regions of the hippocampus and its modulation by environmental enrichment and could contribute to the development of strategies aimed at limiting pathological changes associated with glutamatergic dysfunctions.