Investigação do papel das sharp wave-ripples durante o sono em processos de formação de memória espacial

Abstract

The process of forming declarative memories seems to involve two stages. Initially, information is transiently encoded in the hippocampus and then distributed to associative regions of the cortex, where it is stabilized, integrated and becomes available for long-term access. Sharp wave-ripples (SWRs), high-frequency oscillatory events recorded in the hippocampus, seem to facilitate the communication of hippocampus-cortical networks, promoting the consolidation of memories during sleep. Several studies have reported impaired consolidation when SWRs are suppressed during post-learning sleep. In addition, other studies suggest that SWRs act in synchrony with other cortical oscillatory activities (i.e. delta and spindles). In this context, we propose the hypothesis that selective disruption of the neural activities that make up such dialog, both in the hippocampus and the prefrontal cortex, results in impaired memory consolidation. The objectives of this work were: 1) to develop a software module for online detection of SWRs; 2) to investigate the effects of SWR disturbance during post-learning sleep on episodic memory consolidation; 3) to advance in the establishment of an experimental infrastructure that allows closed-loop cortical disturbance experiments to be carried out with optogenetics. The Part I of this work presents the development and validation of a software module (plugin) for the Open Ephys platform dedicated to detect SWRs in real time. The motion detection mechanism integrated to the plugin was able to concentrate the stimulation system’s functioning in the sleep periods. In Part II, Wistar rats were subjected to ripple disruption during sleep after learning in the Barnes maze. Memory was assessed 24 hours and 12 days after the end of the training stage. Compared to the control group, there was a reduction in the search for holes and in the time spent in the target quadrant after 12 days, but not after 24 hours. The results indicate that only remote memory was affected, suggesting the selective participation of SWRs in the consolidation mechanisms. Part III presents the standardization of methods for carrying out future cortical manipulation experiments following the detection of SWRs. To this end, two animals were transfused with an inhibitory opsin (ArchT) and implanted with an optical fiber for the inhibition of the prefrontal cortex. The developed implant, unlike the traditional ones, favors optogenetic manipulation over long periods and in contexts in which the animal moves more often. Fluorescence analyses confirm ArchT expression, but future work is still needed to validate the inhibition. The results of this work contribute to: 1) establish an experimental infrastructure that makes it possible to test the causal role of oscillatory activities in memory consolidation; 2) elucidate the consolidation processes mediated by SWRs.