GABAA receptor beta 2 and beta 3 subunits mRNA in the hippocampal formation of aged human brain with Alzheimer-related neuropathology.

Our work on the role of glutamate in Alzheimer's disease (AD)-related neuronal vulnerability and death provided significant insight into the potential contribution of the gamma-aminobutyric acid (GABA) neurotransmitter system as it participates in countering the neurotoxic effects of excessive glutamate receptor stimulation. Our previous studies demonstrate that beta2/3 GABAA receptor subunit immunoreactivity is relatively well preserved in hippocampi with AD pathology. To further elucidate the molecular basis for this observation, we employed in situ hybridization histochemistry to examine the levels of beta2 and beta3 receptor subunit mRNAs in the hippocampus of 19 elderly subjects presenting with a broad range of pathologic severity (i.e., Braak stage I-VI). Semi-quantitative analysis with film autoradiograms revealed that beta2 mRNA signal was highest in the granule cell layer, CA2 and CA1 subfields, while beta3 mRNA hybridization was highest in the granule cell layer, followed by CA2>/=CA3>/=CA1 regions. No significant difference in beta2 mRNA expression was detected among the pathologically mild, moderate or severe groups. In contrast, levels of beta3 mRNA in the pathologically severe group was significantly decreased compared to the mild group within all subregions examined except CA4. Our data suggest that alterations in the expression of GABAA receptor subunits in the AD hippocampus differ between specific receptor subunits with the amount of beta2 mRNA being relatively well-preserved, while beta3 mRNA levels were decreased.