Region-Dependent Increase of Cerebral Blood Flow During Electrically Induced Contraction of the Hindlimbs in Rats

Abstract

Elevation of cerebral blood flow (CBF) may contribute to the cerebral benefits of the regular practice of physical exercise. Surprisingly, while electrically induced contraction of a large muscular mass is a potential substitute for physical exercise to improve cognition, its effect on CBF remains to be investigated. Therefore, the present study investigated CBF in the cortical area representing the hindlimb, the hippocampus and the prefrontal cortex in the same anesthetized rats subjected to either acute (30 min) or chronic (30 min for 7 days) electrically induced bilateral hindlimb contraction. While CBF in the cortical area representing the hindlimb was assessed from both laser doppler flowmetry (LDFCBF) and changes in p-eNOSSer1177 levels (p-eNOSCBF), CBF was evaluated only from changes in p-eNOSSer1177 levels in the hippocampus and the prefrontal cortex. The contribution of increased cardiac output and increased neuronal activity to CBF changes were examined. Stimulation was associated with tachycardia and no change in arterial blood pressure. It increased LDFCBF with a time- and intensity-dependent manner as well as p-eNOSCBF in the area representing the hindlimb. By contrast, p-eNOSCBF was unchanged in the two other regions. The augmentation of LDFCBF was partially reduced by atenolol (a ß1 receptor antagonist) and not reproduced by the administration of dobutamine (a ß1 receptor agonist). Levels of c-fos as a marker of neuronal activation selectively increased in the area representing the hindlimb. In conclusion, electrically induced bilateral hindlimb contraction selectively increased CBF in the cortical area representing the stimulated muscles as a result of neuronal hyperactivity and increased cardiac output. The absence of CBF changes in cognition-related brain regions does not support flow-dependent neuroplasticity in the pro-cognitive effect of electrically induced contraction of a large muscular mass.

Cerebral Benefits Induced by Electrical Muscle Stimulation: Evidence from a Human and Rat Study

“…We first investigated neuronal activity and cerebral blood flow increases, since the activation of these two pathways has been extensively demonstrated after classical EX [5,47,55]. Using c-fos as an indicator of neuronal response [56] and the phosphorylated form of eNOS at serin 1177 as a marker of increased cerebral blood flow [57], we were unable to report an effect of EMS on these two pathways, since no variation in the expression of these markers could be found either 4 or 24 h after EMS. Furthermore, although we did not assess this aspect in our human study, neuroimaging approaches reported an activation of the sensorimotor cortex in response to EMS [58,59], without referencing any activation in regions associated with cognition such as the hippocampus, while in contrast, EX was shown to lead to the activation of the hippocampal region up to 20 min after its completion in humans [60].…”

Acute to long-term characteristics of impedance recordings during neurostimulation in humans

“…The observation likely reflects the previously reported phenomena where voltage applied to the microelectrodes reduces the impedance by 'cleaning' the electrode of biological material. The impedance may be further effected by elevated blood flow, as neuronal hyperactivity due to stimulation may increase blood perfusion around the electrodes [38]. Therefore, impedance recovery during the stimulation gaps may be facilitated by decreased metabolic demands and blood perfusion in brain tissue.…”