Hippocampal levels of GluR1 and GluR2 complexes are modulated by training in the multiple T-Maze in C57BL/6J mice

A series of studies has shown the importance of AMPA-type glutamate receptors (AMPARs) for memory formation. The aim of the current study was to show whether GluR1 and GluR2 complexes rather than subunits in mouse hippocampus were involved in training in the multiple T-Maze (MTM). C57BL/6J mice were trained in the MTM and compared to yoked controls. 6 h following the completion of the fourth day training, mice were euthanized, hippocampi were taken and proteins extracted, run on blue native gels with subsequent immunoblotting with antibodies against mouse GluR1 and GluR2. On blue-native western blotting, GluR1 protein was represented by a single band at the apparent molecular weight of about 480 kDa probably indicating a tetrameric assembly. GluR2 protein was represented by a single band between apparent molecular weights of 480 and 720 kDa indicating a homo- or heteropolymer probably with other AMPAR or regulatory subunits. In mice trained in the MTM, protein levels for GluR1 were significantly increased while GluR2 levels were significantly decreased. On two-dimensional (2D) gel electrophoresis, the presence of GluR1 and GluR2 were identified by mass spectrometry, and 2D immunoblotting revealed several expression forms of these receptor subunits. Findings unequivocally show that GluR1 and GluR2 complexes are linked to training in the MTM in C57BL/6J mice. These results may not only form the basis for studying receptor complexes rather than receptor subunits in memory formation or mechanisms of potential cognitive enhancers but represent a tool for investigations into pharmacological studies including the use of glutamate receptor agonists and antagonists.