Generation and characterization of a specific polyclonal antibody against the mouse serotonin receptor 1A: A state-of-the-art recommendation on how to characterize antibody specificity

Different expression of membrane-bound and cytosolic hippocampal steroid receptor complexes during spatial training in young male rats

Brain steroid receptors are involved in mediating stress responses and cognitive processes throughfast non-genomic signaling of membrane-bound receptors or through the slower genomic actions of cytosolic receptors. Although the contribution of these different pathways in the formation and maintenance of memories has been widely discussed, little is known about the regulation of membrane versus cytosolic receptors during a learning task. Besides the relatively well studied corticosterone-binding glucocorticoid (GR) and mineralocorticoid (MR) receptors, sex steroid hormone receptors, such as the androgen and estrogen (ERα and ERβ) receptors, have also been shown to be involved in the regulation of stress and cognition. Moreover, the latter receptors are known to be functional in both sexes. Therefore, we studied the expression of hippocampal receptors in both cellular fractions during spatial learning in male rats. Membrane and cytosolic GR were shown to be downregulated after memory acquisition and unaffected after consolidation, whereas membrane MR was upregulated after both learning phases and unaffected in the cytosol. Cytosolic ERα was downregulated after both phases and unaffected in the membrane. The remaining receptors were not regulated. The data suggest a specific role of MR and ERα during training as fast and slow mediators, respectively.

A hippocampal nicotinic acetylcholine alpha 7-containing receptor complex is linked to memory retrieval in the multiple-T-maze in C57BL/6j mice

The link between the cholinergic and serotonergic system in cognitive function is well-documented. There is, however, limited information on spatial memory and this formed the rationale to carry out a study with the aim to show a specific link between nicotinic and serotonergic receptor complexes rather than the corresponding subunits, to spatial memory retrieval in a land maze. A total of 46 mice were used and divided into two groups, trained and untrained (yoked) in the multiple-T-Maze (MTM) and following training during the first four days, probe trials for memory retrieval were performed on days 8, 16 and 30. Six hours following scarification, hippocampi were taken for the analysis of native receptor complex levels using blue-native gels followed by immunoblotting with specific antibodies. 5-HT1A-, 5-HT7-, nAChα4- and nACh-α7-containing receptor complexes were observed and were paralleling memory retrievals and receptor complex levels were shown to be significantly different between trained and yoked animals. Only levels of a nicotinic acetylcholine α7 receptor-containing complex at an apparent molecular weight of approximately 480kDa were shown to be linked to memory retrieval on day 8 but not to retrievals on days 16 and 30 when memory extinction has taken place. Correlation between nAChα4-, 5-HT1A- and 5-HT7-containing receptors and latencies on day 16 may point to a probable link in extinction mechanisms. A series of the abovementioned receptor complexes were correlating among each other probably indicating a serotonergic/cholinergic network paralleling spatial memory formation.

Hippocampal glutamate transporter 1 (GLT-1) complex levels are paralleling memory training in the Multiple T-maze in C57BL/6J mice

The glutamate transporter 1 (GLT-1) is essential for glutamate uptake in the brain and associated with various psychiatric and neurological disorders. Pharmacological inhibition of GLT-1 results in memory deficits, but no study linking native GLT-1 complexes was published so far. It was therefore the aim of the study to associate this highly hydrophobic, eight transmembrane spanning domains containing transporter to memory training in the Multiple T-maze (MTM). C57BL/6J mice were used for the spatial memory training experiments, and trained mice were compared to untrained (yoked) animals. Mouse hippocampi were dissected out 6 h after training on day 4, and a total enriched membrane fraction was prepared by ultracentrifugation. Membrane proteins were separated by blue native polyacrylamide gel electrophoresis (BN-PAGE) with subsequent Western blotting against GLT-1 on these native gels. Moreover, GLT-1 complexes were identified by mass spectrometry (nano-LC-ESI-MS/MS). Animals learned the MTM task and multiple GLT-1 complexes were detected at apparent molecular weights of 242, 480 and 720 kDa on BN-PAGE Western blotting. GLT-1 complex levels were significantly higher in the trained group as compared to yoked controls, and antibody specificity was verified by immunoblotting on multidimensional gels. Hippocampal GLT-1 was unambiguously identified by mass spectrometry with high sequence coverage, and glycosylation was observed. It is revealed that increased GLT-1 complex levels are paralleling and are linked to spatial memory training. We provide evidence that signal termination, represented by the excitatory amino acid transporter GLT-1 complexes, is involved in spatial memory mechanisms.

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.