Subregional analysis of GABA(A) receptor subunit mRNAs in the hippocampus of older persons with and without cognitive impairment.

We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal mRNA expression of GABA(A) receptor subunits alpha1 and alpha5 in human subjects with progressing cognitive impairment. Included in this study were 17 participants of the Religious Order Study (ROS), who were categorized into three groups based upon degree of cognitive impairment: no cognitive impairment (n = 6); moderate cognitive impairment (n = 5); and probable Alzheimer's disease (AD) (n = 6). While the levels of each specific subunit mRNA were relatively homogeneously distributed throughout the five hippocampal subregions analyzed (CA1-4, and the granule cell layer of the dentate gyrus), mRNA expression of the alpha1 receptor subunit was found to be 20% reduced in the moderate cognitive impairment group as compared to the no cognitive impairment group. In addition, alpha1 mRNA expression was 25% reduced in the probable Alzheimer's disease group compared to the group with no cognitive impairment. Similarly, alpha5 subunit mRNA was reduced 32% between no cognitive impairment and moderate cognitive impairment groups, and 35% between no cognitive impairment and probable Alzheimer's disease groups. No significant reductions were found between moderate cognitive impairment and probable Alzheimer's disease groups for either subunit. Collectively, our data provide evidence for modest reductions in GABA(A) receptor subunit mRNAs, and suggest these changes occur very early in the progression of Alzheimer's disease cognitive impairment.