| Abstrakt: |
Background: Hyperexcitability and glutamate excitotoxicity are the primary contributors towards synapse loss in Alzheimer's disease (AD). The goal of this project is to examine how other neurotransmitter systems, such as the inhibitory GABAergic system, are responding to hyperexcitability in AD. Therefore, we examined the role of metabotropic GABAB receptors (GABABRs) towards synapse loss. Methods: Primary hippocampal neurons were cultured from both wildtype (WT) and transgenic APP/PS1 mice. In addition, treatment of non‐transgenic hippocampal neurons with Aβ oligomers (500nM) were used as another model of AD‐related pathology. Immunocytochemistry was used to determine the dendric expression of GABAB1R and GABAB2R, the two principal subunits of GABABRs. To examine changes in GABABR function, a calcium imaging protocol was utilized to quantify changes in calcium florescence following GABABR activation with baclofen (50μM). To understand whether GABABR activation is protective against synaptic loss in AD, APP/PS1 hippocampal neurons were treated with 50μM baclofen (GABABR agonist), 100μM CGP35348 (GABABR antagonist), or vehicle. This study used both colocalization of presynaptic (Synapsin‐1) and postsynaptic (PSD95) markers as well as a novel method, DetectSyn, to quantify changes in synaptic density. Results: Dendritic GABAB1R and GABAB2R expression is upregulated in APP/PS1 hippocampal neurons as compared to WT. Non‐transgenic neurons treated with Aβ‐oligomers also show upregulations in GABAB2R, with no changes in GABAB1R. Treating WT neurons with baclofen resulted in an approximate 10% decrease in calcium florescence. The same treatment applied to APP/PS1 neurons resulted in a significantly greater decrease (∼40%) in calcium florescence. Activating GABABRs in APP/PS1 neurons increased synaptic density as compared to vehicle treated neurons. This was indicated by a greater Pearson's coefficient between Synapsin‐1 and PSD95, as well as a greater number of DetectSyn‐PLA puncta. Antagonizing GABABRs in APP/PS1 neurons failed to rescue synaptic density (no changes in Pearson's coefficient/DetectSyn‐PLA puncta) when compared to vehicle treated neurons. Conclusions: Under pathological conditions, upregulation and activation of GABABRs serves as a potential mechanism to combat against hyperexcitability, therefore preventing hippocampal synaptic loss in AD. [ABSTRACT FROM AUTHOR] |
