Perturbation of Circadian Neuronal Oscillators with Low-Intensity Magnetic Stimulation

Abstract

Circadian neuronal oscillatory dynamics are perturbed substantially in numerous neuropsychiatric diseases, such as Alzheimer's, Parkinson's, and depression. Moreover, desynchronization of neuronal oscillators complicates or hinders an effective treatment to many brain disorders. In humans, the roughly 20,000 neurons in the suprachiasmatic nucleus (SCN) are circadian oscillators that control daily oscillations in hormone secretion, maintenance of body temperature, blood pressure, cell division, and the sleep-wake cycle. Abnormal dynamics in neuronal networks can be re-organized or perturbed towards normal activity by magnetic stimulation. Repetitive transcranial magnetic stimulation (rTMS) is a non-pharmacological and non-invasive method of activating different brain regions to alleviate neurological disorders. Our present research sought to restore abnormal circadian neuronal oscillatory dynamics by exposing the SCN to our custom-built low-intensity rTMS (Li-rTMS) at different circadian times. We utilized Li-rTMS parameters (25 Hz, B=15 mT, and E=2.0 V/m) in vivo and in vitro to determine if stimulation re-organized abnormal SCN output toward normalcy. Li-rTMS was applied to wild-type (WT) mice with normal SCN output and compared with abnormal Tat-transgenic mice output via evaluation of c-Fos protein expression to delineate and confirm the activated brain regions. Additionally, we stimulated SCN tissues from WT and Tat mice in vitro and measured the neuronal electrical activity to assess perturbations in clock output oscillation patterns. Further, we evaluated the effect of Li-rTMS (nicknamed Li-MS during our in vitro SCN explant work) on clock proteins by stimulating SCN tissue explants from PERIOD2::LUCIFERASE (PER2::LUC) transgenic mice and measured the bioluminescence of PER2 clock protein. Our result from c-Fos protein expression analysis showed that Li-rTMS could activate neurons in the SCN and this activation was dependent on the phase of the circadian oscillatory activity. Recording of spontaneous firing rate from SCN slices also showed that samples exposed to Li-rTMS had a significant change in amplitude, phase, and period, compared to unexposed samples. Furthermore, molecular clock results demonstrated that Li-rTMS could significantly modulate the phase and amplitude of PER2::LUC oscillation. Our findings imply that LirTMS might be used to reset biological clocks, and thus, could be instrumental in remedying insomnia, neurological, and mental disorders.