OBJECTIVE: Determine whether in the hippocampus and the supramammillary nucleus (SuM) the same neurons are reactivated when mice are exposed 1 week apart to two periods of wakefulness (W-W), paradoxical sleep rebound (PSR-PSR) or a period of W followed by a period of PSR (W-PSR).
METHODS: We combined the innovative TRAP2 mice method in which neurons expressing cFos permanently express tdTomato after tamoxifen injection with cFos immunohistochemistry.
RESULTS: We found out that a large number of tdTomato+ and cFos+ cells are localized in the dentate gyrus (DG) after PSR and W while CA1 and CA3 contained both types of neurons only after W. The number of cFos+ cells in the infrapyramidal but not the suprapyramidal blade of the DG was positively correlated with the amount of PS. In addition, we did not find double-labeled cells in the DG whatever the group of mice. In contrast, a high percentage of CA1 neurons were double-labeled in W-W mice. Finally, in the supramammillary nucleus, a large number of cells were double-labeled in W-W, PSR-PSR but not in W-PSR mice.
CONCLUSIONS: Altogether, our results are the first to show that different neurons are activated during W and PS in the supramammillary nucleus and the hippocampus. Further, we showed for the first time that granule cells of the infrapyramidal blade of the DG are activated during PS but not during W. Further experiments are now needed to determine whether these granule cells belong to memory engrams inducing memory reactivation during PS.

Water temperature is one of the most important environmental factors affecting the growth and survival of fish. Increased water temperature became a global problem and it is estimated that there will be an increase in water temperature due to global climate change. The physiological mechanism for the effects of high water temperature on the fish brain is not fully known. In the present study, fish were exposed to different temperatures (10 °C/15 °C/20 °C/25°) and brain tissues were sampled 2 h-4h-6h-8h per hour respectively and then we investigated transcriptional changes of BDNF, cFOS, apoptotic genes (caspase 3, Bax, Bcl2), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1) and oxidative stress genes (CAT, SOD, and GPx) and also immunoflourescence changes of BDNF and cFOSin rainbow trout brain. The results indicated that high temperature stress lead to physiological changes in the fish brain by causing a decrease in mRNA expression levels of CAT, SOD, GPx and Bcl2 and by causing an increase in mRNA expression of BDNF, cFOS, apoptotic genes (caspase 3, Bax), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1). This study will provide important information to elucidate the physiological mechanisms related to the effects of high water temperature on the fish brain.