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

Abstract

AbstractThe 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 certain times of the day is beneficial for maintaining circadian health; however, the underlying mechanisms in diurnal species such as humans are poorly understood. We therefore investigated the effect of behavioral activity on SCN neuronal firing rate in the diurnal rodent Arvicanthis ansorgei by performing in vivo electrophysiological recordings in freely moving animals. We found that SCN firing was acutely increased at the onset of behavioral activity; the firing rate remained elevated during episodes of behavioral activity ranging from seconds to hours, and then returned to baseline levels after behavioral activity ceased. We also found that diurnal behavioral input increases SCN rhythm amplitude, while crepuscular activity results in a bimodal rhythm in the SCN. To confirm that behavioral activity affects the SCN via activation of extra-SCN areas, we performed ex vivo recordings and found that SCN firing in both fully diurnal and crepuscular animals has a unimodal rhythm, with a single peak occurring at midday. Together, these data indicate that exercise increases the SCN’s rhythm in diurnal Arvicanthis and does so via an excitatory effect on the SCN’s neuronal firing rate. Thus the electrical activity rhythm that is generated at a molecular level is increased by behavioral activity.