Abstract
BACKGROUND: Depression involves abnormal neural oscillations. Photobiomodulation (PBM) modulates such oscillations but lacks behavioral electrophysiological mechanistic studies. We explored PBM's effects on hippocampal CA1 oscillations and phase-amplitude coupling (PAC) in a depression model. METHODS: Male C57BL/6J mice were randomly divided into saline, LPS (2 mg/kg i.p.), and LPS + PBM groups (n = 10/group for behavioral tests, n = 8/group for electrophysiology). LPS groups received lipopolysaccharide to induce neuroinflammation. The LPS + PBM group underwent 810 nm PBM (20 mW/cm², 12 min/day × 4 days) starting day 4 post-injection. Anxiety- and depression-like behaviors were assessed via open field, elevated plus-maze, and tail suspension tests. Wireless electrophysiology recorded CA1 local field potentials (LFP) during rest and behaviors. Oscillations and PAC were analyzed. Data are presented as mean ± SD; group differences were evaluated by one-way ANOVA with Bonferroni post-hoc correction and ɳ² effect sizes, with two-tailed p < 0.05 taken as statistically significant. RESULTS: PBM (20 mW/cm(2)) alleviated LPS-induced anxiety and depressive behaviors. Electrophysiologically, PBM restored resting-state δ power (LPS + PBM: 0.0499 ± 0.0282, LPS: 0.1491 ± 0.0887; p < 0.01) and enhanced δ-γ coupling (LPS + PBM: 2.049 ± 0.447, LPS: 0.230 ± 0.298; p < 0.05). During anxiety tasks, PBM suppressed γ power (LPS + PBM: 0.3709 ± 0.1569, LPS: 0.5165 ± 0.06896; p < 0.05) and strengthened δ-γ PAC (LPS + PBM: 0.741 ± 0.508 vs. LPS: 0.217 ± 0.218, p < 0.05). In depression tests, PBM normalized δ power (LPS + PBM: 0.0261 ± 0.0182, LPS: 0.1315 ± 0.0619; p < 0.001) and reduced γ power (LPS + PBM: 0.2848 ± 0.0921, LPS: 0.4067 ± 0.0892; p < 0.05). No significant PAC changes was observed during depression tasks. CONCLUSION: PBM therapy ameliorates LPS-induced depression and anxiety behaviors while normalizing hippocampal CA1 oscillations and cross-frequency coupling. Its effects are state-dependent, modulating distinct frequency bands and PAC across rest and behavioral contexts, revealing potential electrophysiological therapeutic mechanisms.