Estudo do potencial de campo local do hipocampo de ratos associado a corrida em esteira e ao efeito do exercício sobre o sono REM

Abstract

In this thesis, we aim to study how instantaneous velocity and acceleration during treadmill running modulate hippocampal theta oscillations. Additionally, we investigate the effects of a training protocol on REM sleep and its tonic and phasic subdivisions. In the first chapter of this thesis we present a manuscript in preparation in which we examine the effect of treadmill locomotion speed on the frequency and power of the hippocampal theta rhythm. This work contributes to an ongoing debate regarding the relationship between hippocampal theta power and frequency with acceleration and instantaneous velocity, as discussed in previous studies such as Kropff et al. (2021) and Kennedy et al. (2022). To this end, bilateral electrode arrays were implanted in five adult male Wistar rats, allowing the recording of local field potentials (LFP) in the dorsal hippocampus during running at three different acceleration rates and three distinct speeds. In this chapter, we conclude that the transition from a stationary state to ambulatory movement leads to a sustained increase in power and a transient increase in the frequency of the hippocampal theta rhythm. Furthermore, we found that instantaneous velocity, rather than acceleration, determines the frequency of the hippocampal theta rhythm. In the second chapter, we evaluate the effects of treadmill running training on hippocampal theta and gamma rhythms during REM sleep. We used electrode arrays to record LFP in the hippocampus and left frontal cortex of eight Wistar rats during sleep over a 12-hour light phase, both before and after a 28-day exercise protocol. We observed that the exercise protocol resulted in a significant reduction in total REM sleep time and in the global LFP power (0-110 Hz) in the CA1 region of the hippocampus during phasic REM sleep. To date, we have not identified previous studies addressing the effects of physical exercise on hippocampal oscillatory rhythms during tonic (4-10 Hz) or phasic (6-12 Hz) REM sleep. Additionally, we found that theta power during phasic REM sleep showed significant correlations with total phasic REM sleep time, as well as with the number and average duration of phasic REM sleep events, but only after the 28-day training period. Together, our results demonstrate the impact of velocity and acceleration on the spectral characteristics of the theta rhythm, as well as the effects of intense physical exercise on theta rhythm during REM sleep and its tonic and phasic subdivisions. These findings support previous studies linking hippocampal theta rhythm to locomotion speed and expand our understanding of the influence of physical exercise on theta rhythm during REM sleep.