Stress typically indicates a demand to adapt to challenges found in everyday life. However, when the stress is uncontrollable, unpredictable, and chronic it can increase the brain's vulnerability to disease.
Dagyte et al. over at the University of Groningen investigated the effects of acute and chronic foot-shock stress on neural plasticity by using hippocampal cell proliferation and neurogenesis data collected from rats. They found that repeated, but not acute exposure to foot-shock stress caused a temporary suppression of Ki-67-positive cell proliferation in the dentate gyrus and a reduction in DCX expression.
The authors suggest that a long-term accumulation of the stressors effects on hippocampal cell proliferation may ultimately compromise hippocampal circuitry. So make sure to stay away from chronic stress if you love your hippocampus and all the important things it does for you.
Dagyte G, Van der Zee EA, Postema F, Luiten PG, Den Boer JA, Trentani A, & Meerlo P (2009). Chronic but not acute foot-shock stress leads to temporary suppression of cell proliferation in rat hippocampus. Neuroscience, 162 (4), 904-13 PMID: 19482059