Effects of sleep deprivation on the cell cycle of neural precursor cells: modulation by caffeine and consequences on memory

Abstract

Sleep deprivation (SD) for long periods has several consequences for the organism, among them the reduction of hippocampal neurogenesis (HN). Animal models show that new neurons formed in the hippocampus play an important role in cognitive functions and mood. During the process of neurogenesis the cells go through several phases, a phenomenon known as cell cycle, and the rate of progression through this cycle is determinant for the fate of the cells formed. Although several studies have investigated the effect of SD on HN, little is known about the effect of prolonged periods of SD on cell cycle progression and rhythm. Therefore, the main objective of this work is to evaluate the impact of SD on the cell cycle of neuronal precursor cells of the hippocampus. Considering the role of HN for memory formation and the memory impairment caused by SD, it is also necessary to investigate a possible correlation between the changes observed in the cell cycle and the performance in a memory task. Another goal of this project is to seek a mediator for the effects of SD on the cell cycle. Adenosine is an important regulator of the sleep-wake cycle whose levels increase during SD, and the involvement of this neuromodulator in the memory impairment caused by SD has already been shown, including by studies developed by this research group. In view of this, we propose to test the involvement of adenosine, as well as two enzymes that participate in intracellular signaling pathways controlled by it, in the effects of SD on the cell cycle and memory. To accomplish these goals, we propose to submit adult Wistar rats to PS through the modified multiple platform method. During this time the animals will receive daily intraperitoneal injections of saline or caffeine, an adenosine receptor antagonist. At the end of SD half of the animals will be euthanized for collection of material, the other half will undergo the task of contextual fear conditioning (CFC) before euthanasia and tissue collection. Neural stem cells isolated via cell sorting flow cytometry will be used to compare levels of the major proteins involved in cell cycle regulation (cyclins and CDKs) and the phosphorylation of two distinct signaling pathway kinases (ERK and mTOR) via western blotting. Tissue isolated from other animals will be used to measure proliferation of the dentate gyrus cells by immunofluorescence using the TissueFAXS system. Finally, animals submitted to the same SD protocol, administration of caffeine and CFC will be euthanized 21 days after the end of SD or the CFC task. The material will be used to perform immunofluorescence in order to evaluate cell differentiation. With this we hope to identify the effect of SD on the cell cycle of the neural precursors of the hippocampus and to relate the alterations found with the alterations in HN and memory impairment, in addition to a better understanding of the role of adenosine in these phenomena. (AU)