Molecular Mechanisms of NMDA Receptor-Mediated β Oscillations in the Subthalamic Nucleus During Exhaustive Exercise

Objective: To investigate the changes in NMDA/GABAA receptor expression in the subthalamic nucleus (STN) under exercise-induced exhaustion and its molecular mechanisms mediating β oscillations (12～30 Hz) in the cortico-basal ganglia pathway of rats. Methods: A modified Bedford incremental load training protocol was used to create an exercise-induced exhaustion model in rats. Immunoblotting was employed to detect changes in NMDA and GABAA receptor expression in the STN of rats after different durations of exhaustive exercise. In combination with pharmacological targeting interventions and in vivo multi-channel neural signal recording techniques, the effects of NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid(APV) and artificial cerebrospinal fluid (aCSF) injections into the STN were compared on the duration, distance, and local field potentials (LFPs) in the cortico-basal ganglia during an exhaustive exercise. Power spectral density (PSD) analysis was conducted to examine the changes in synchronized oscillatory activity across different frequency bands of various nuclei during exhaustive exercise. Synchronization likelihood (SL) analysis was used to explore the functional connectivity changes in the cortico-basal ganglia network. Results: 1) Immunoblotting results showed that, compared to the resting group, the expression of the NMDA receptor GluN2B subunit in the STN significantly increased with prolonged exercise duration (day 7: P＜0.01), while the GABAA receptor α1 subunit showed no significant change (P＞0.05), resulting in an imbalance in the NMDA/GABAA receptor ratio (P＜0.05); 2) after pharmacological intervention in the STN, analysis of the rats’ motor performance revealed that, compared to the aCSF group, the NMDA receptor antagonist APV intervention group exhibited significant increases in Load increase phase & autonomous movement phase and early fatigue phase（P＜0.05), while no significant differences were observed in the exhaustion phase. PSD analysis revealed a significant reduction in the PSD values in the β frequency band only in the primary motor cortex (M1), external globus pallidus (GPe), and STN (P＜0.05). SL analysis showed a significant decrease in the average SL coefficients of the indirect pathway (Str-GPe, GPe-STN, GPe-SNr, STN-SNr) and hyperdirect pathway (M1-STN) in the β frequency band (P＜0.05), while no significant differences were observed in the direct pathway (Str-SNr) (P＞0.05). Conclusions: In an exhausted state, excessive NMDA receptor expression in the STN disrupts the excitation-inhibition balance in the GPe-STN microcircuit, thereby inducing β synchronized oscillations in the cortico-basal ganglia pathway. This occurs through the selective enhancement of functional connectivity in the hyperdirect and indirect pathways, inhibiting motor output. The upregulation of NMDA receptors in the STN may be a key molecular mechanism underlying β oscillation generation. This study provides new experimental evidence for understanding the molecular-circuit mechanisms of exercise-induced exhaustion and offers potential targets for the development of related intervention strategies.