Behavioral activity increases neuronal activity in the circadian clock of diurnal Arvicanthis ansorgei

2.The central circadian clock, located in the suprachiasmatic nucleus (SCN) within the brain, regulates daily patterns of activity and physiology. Many studies indicate that exercise at specific times throughout the day can help maintain proper circadian rhythms. In nocturnal animals, even moderate levels of physical activity suppress the neuronal discharge rate of the SCN. Given that such a mechanism would likely be counter-effective in diurnal animals, we measured the firing rate of SCN neurons in freely moving diurnal Arvicanthis ansorgei using implanted microelectrodes. We found that SCN firing was acutely increased rather than decreased both during brief (seconds) and long (hours) bouts of activity, and returned to baseline levels after behavioral activity ceased. We also found that daytime activity increases the strength of the SCN rhythm, as expected for day-active animals. To determine whether the acute increases in firing are produced within the SCN or in response to input from outside the SCN, we performed ex vivo recordings in which afferent inputs are severed. We found no intrinsic increment occurring in the isolated SCN. These findings suggest that the excitatory effect on the SCNs neuronal firing rate comes from areas that lie outside the SCN, presumably those that are affected by the animals activity. We conclude that exercise has opposite effects on the clock between nocturnal and diurnal rodents, and identified how exercise strengthens the neuronal discharge rhythm in the clock of a diurnal animal. 3. Significance statementOur biological clock controls behavioral activity rhythms by generating a 24-pattern of electrical activity. The electrical activity serves as output of the clock and is high during the day and low during the night. Physical activity, being under strong control of the clock, acts vice versa, and affects the electrical activity of the clock. In nocturnal animals, behavioral activity inhibits the clocks firing rate. Here, we examined the effect of behavioral activity on the brains clock in the diurnal rodent, Arvicanthis. When the animal is active, the clocks electrical activity is enhanced, rather than decreased. Thus, a diurnal animal can increase the strength of its own clock, by being active during the day. Preprint ServersThe manuscript was deposited as a preprint in bioRxiv preprint doi: https://doi.org/10.1101/2022.05.31.493966; this version posted June 1, 2022. The copyright holder for this preprintin bioRxiv, made available under aCC-BY-NC-ND 4.0 International license (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. ClassificationBiological Sciences, Physiology