Glutamate receptor subunit and calmodulin kinase II expression, with and without T maze training, in the rat hippocampus following bilateral vestibular deafferentation

Abstract

Many previous studies have shown that lesions of the peripheral vestibular system result in spatial memory deficits and electrophysiological dysfunction in the hippocampus. Given the importance of glutamate as a neurotransmitter in the hippocampus, it was predicted that bilateral vestibular deafferentation (BVD) would alter the expression of NMDA and AMPA receptors in this area of the brain.

Methods: The expression of the NR1, NR2A, NR2B, GluR1, GluR2, GluR3 and GluR 4 glutamate receptor subunits, as well as calmodulin kinase IIα (CaMKIIα) and phosphorylated CaMKIIα (pCaMKIIα), was measured in the rat CA1, CA2/3 and dentate gyrus (DG) subregions of the hippocampus, at 24 h, 72 h, 1 week, 1 month and 6 months following BVD, using western blotting. In the 6 month group, half of the animals underwent spatial forced alternating training in a T-maze.

Results and discussion: For the 24 h, 72 h, 1 week and 1 month data, there was no significant effect of surgery for any hippocampal subregion. However, for the 6 month data set, T maze training had a significant effect independently of surgery. The results of these experiments suggest that BVD is not associated with large changes in glutamate receptor subunit or CaMKIIα expression in the rat hippocampus, at least in terms of both the intra-cytoplasmic and membrane receptor subunits together, that western blotting can measure. However, spatial training-associated increases in glutamate receptor and CaMKIIα expression can be induced in BVD rats with impaired spatial performance. Therefore, the neurophysiological changes underlying BVD-induced spatial learning and memory deficits are more likely to be due to up and down regulation or changes in affinity/efficacy of glutamate receptors at the membrane level than changes in subunit transcription and transduction at the intra-cytoplasmic level.

Figure 1. Mean normalized density of expression of NR1, NR2A, NR2B, GluR1, GluR2, GluR3, GluR4, CaMKIIα and pCaMKIIα in the CA1, CA2/3 and DG regions of the hippocampus at 24 h, 72 h and 1 week following BVD or sham surgery.

Error bars represent 95% confidence intervals for the mean.

Figure 2. Mean normalized density of expression of NR1, NR2B, GluR1, GluR2, GluR3, CaMKIIα and pCaMKIIα in the CA1, CA2/3 and DG regions of the hippocampus at 6 months following BVD or sham surgery for animals trained in a T maze or not trained in a T maze.

Error bars represent 95% confidence intervals for the mean.

Figure 3. Example of western blots for CamKIIα and pCaMKIIα in CA2/3 for the BVD (‘B’) and sham (‘S’) animals that received T maze training or no T maze training at 6 months post-op.

‘IS’ is the internal standard and β-actin (‘Actin’) is also shown.

Figure 4. Cluster analysis, using the correlation coefficient distance and Ward’s minimal variance algorithm, on the neurochemical data at 6 months post-op. for the CA1, CA2/3 and the DG data together, showing the relationship between the different neurochemical variables as z scores (zCaMKII etc) for the sham (A) and BVD (B) animals.

Note that there is no difference between the clusters for the sham and BVD animals.

Figure 5. Cluster analysis, using the correlation coefficient distance and Ward’s minimal variance algorithm, on the neurochemical data at 6 months post-op. in CA2/3, showing individual animals according to training (T maze or no T maze).

Note that the neurochemical data for CA2/3 can completely distinguish the trained from the non-trained animals.