In addition, an “early” SASP, such as p38, and a “late” SASP, such as NF-κB, both markers of microglial senescence, were increased after 14 and 28 days, respectively.40 Studies on animal models subjected to depression showed that in the hippocampus, but not in other brain regions, there was an initial activation of microglia followed by an apoptotic decline of these cells and a reduction in activity, caused by a reduction in the cell number, about 5 weeks later. The gene discussed is NFKB1; the disease is major depressive disorder.