Effects Of Glucose Deprivation And Creatine Supply On Cortical Neurons Excitability

Objective: The exercise-induced central fatigue leads to shortage of brain energy and decrease of motor cortex excitability. Large-conductance Ca²⁺- and voltage-activated K⁺(BK_Ca) channels are widely expressed in the central nervous system and play important roles in controlling action potential duration, firing frequency and spike frequency adaptation. This study aims to investigate the function of BK_Ca channels on neuronal excitability during glucose deprivation and the neuro-protection of creatine supply when glucose is withdrawn.Methods :（1） Multi-channel recording system was used to record local field potentials（LFPs） and neuronal excitability in primary motor cortex（M1） during exhausting exercise.（2） Patch-clamp technology was applied to observe the excitability changes of Betz cell in M1 brain slice of adult rats.（3） We also used primary cultured rat cortical neurons to test BK_Ca currents and Ca²⁺ concentration withapplication of exogenous creatine in glucose-free solution.Results:（1） Compared to rest condition, the total power of LFPs significantly decreased（P < 0.05）when the rats get exhausted. And the δ and θ wave increased but β wave decreased（P < 0.01）.Meanwhile the firing frequency of pyramidal neurons reduced（P < 0.01）.（2） Removal of bath glucose（0.5h-1h） lowered the excitability of Betz cell in M1.Both Threshold and Rheobase decreased, while the peak amplitude offast After-Hyperpolarizing Potential（f AHP） increased（P < 0.01）.（3） The current density of BK_Ca channels significantly increased after glucose deprivation for 1h- 2h but decreased after 4h（P < 0.01） compared to their Control groups. The concentration of Ca²⁺ increased over time（1h-5h, P < 0.01）.（4） Compared with glucose deprivation brain slices, Only pre-incubation with creatine for 30 min followed by glucose removal could increased（ P < 0.01） the Betz cell excitability significantly,while,adding creatine in glucose-free solution at the same time wouldn’t have the same effect. What’s more, after 24 h treatment with creatine, the current density of BK_Ca channels and Ca²⁺ were much lower（P < 0.01）than no-creatine treatment groups in the same time interval when glucose was depredated.Conclusion: The data indicates that（1） One-time exhaustive swimming will reduce the neuronal excitability of M1.（2） Glucose deprivation for 1h- 2h can excessively trigger calcium overload together with the over-activation of BK_Ca channels in cortical pyramidal neurons, which will result in the rapid hyperpolarization and the reduction of excitability.（3） Creatine pretreatment can lessen BK_Ca currents and influx of extracellular calcium during glucose deprivation, protecting neurons from injury induced by glucose deprivation.