Frontal EEG alterations induced by hippocampal amyloid pathology in rats

Purpose

In this study, it was aimed to determine the dose-dependent effects of hippocampal amyloid beta (Aβ) on frontal EEG activity and to elucidate the possible non-invasive biomarkers by recording spontaneous EEG in free-moving rats.

Material and methods

Male albino Wistar rats aged 3 months were randomly divided into 4 groups (n ​= ​8 for each group), obtained by intrahippocampal injection of saline or different doses of Aβ_1-42 i.e. 0.01 ​μg/μl, 0.1 ​μg/μl, and 1 ​μg/μl. After two weeks of recovery period, spontaneous EEG recordings were obtained from frontal regions and spectral power analyses were performed.

Results

We detected a general slowdown in the brain activity two weeks after Aβ_1-42 injection.

We observed significant increases in frontal alpha power (p ​= ​0.0021) and significant decreases in frontal beta power (p ​= ​0.0003) between the Sh and Aβ_1-42-injected groups. More specifically, the ratio of the frontal EEG beta and alpha power (rFBA) was significantly affected by the intrahippocampal injection of Aβ_1-42 (p ​< ​0.0001). Also, we observed that rFBA was negatively and strongly correlated with hippocampal Aβ_1-42 peptide levels (r ​= ​−0.781, p ​< ​0.0001).

Conclusion

Our findings indicate that spontaneous frontal EEG beta and alpha activity were significantly affected by the intrahippocampal injection of Aβ_1-42. However, the results suggest that the power ratios of these bands are more sensitive to the hippocampal amyloid pathology. As such, it is proposed that the rFBA may be a more effective biomarker for diagnosing hippocampal pathology induced by Aβ_1-42.