AMPA RECEPTOR PROPERTIES IN ADULT-RAT HIPPOCAMPUS FOLLOWING ENVIRONMENTAL ENRICHMENT

In adult rats, environmental enrichment has been shown to selectively increase H-3-AMPA binding in the hippocampus but the molecular mechani sms underlying this effect remain unknown. We used in situ hybridizati on with antisense oligonucleotides to determine possible changes in th e hippocampal expression of messenger RNAs for different subunits of A MPA receptors in adult rats following exposure to an enriched environm ent. Quantitative analysis revealed that mRNA levels for three subtype s of AMPA glutamate receptors (GluR1-3; Flip and Flop variants) were n ot modified in any hippocampal region after environmental enrichment. In addition, no differences were detected in the levels of GluR1 and G luR2/3 proteins in Western blots of hippocampal membranes from enriche d rats. Nevertheless, quantitative ligand binding autoradiography indi cated that environmental enrichment evoked a significant and uniform d ecrease in the capacity of calcium or phosphatidylserine (PS) to up-re gulate H-3-AMPA binding in various hippocampal regions but not in the cerebral cortex. These findings support previous observations suggesti ng that post-translational changes in AMPA receptor properties, as a r esult of the activation of calcium-dependent processes, may represent an important mechanism underlying long-term modifications of synaptic efficacy in the rat hippocampus. (C) 1998 Published by Elsevier Scienc e B.V. All rights reserved.