Physical exercise leads to rapid adaptations in hippocampal vasculature: Temporal dynamics and relationship to cell proliferation and neurogenesis

Strategies to promote differentiation of newborn neurons into mature functional cells in Alzheimer brain

Adult neurogenesis occurs in the subgranular zone (SGZ) and subventricular zone (SVZ). New SGZ neurons migrate into the granule cell layer of the dentate gyrus (DG). New SVZ neurons seem to enter the association neocortex and entorhinal cortex besides the olfactory bulb. Alzheimer disease (AD) is characterized by neuron loss in the hippocampus (DG and CA1 field), entorhinal cortex, and association neocortex, which underlies the learning and memory deficits. We hypothesized that, if the AD brain can support neurogenesis, strategies to stimulate the neurogenesis process could have therapeutic value in AD. We reviewed the literature on: (a) the functional significance of adult-born neurons; (b) the occurrence of endogenous neurogenesis in AD; and (c) strategies to stimulate the adult neurogenesis process. We found that: (a) new neurons in the adult DG contribute to memory function; (b) new neurons are generated in the SGZ and SVZ of AD brains, but they fail to differentiate into mature neurons in the target regions; and (c) numerous strategies (Lithium, Glatiramer Acetate, nerve growth factor, environmental enrichment) can enhance adult neurogenesis and promote maturation of newly generated neurons. Such strategies might help to compensate for the loss of neurons and improve the memory function in AD.

The effects of exercise on adolescent hippocampal neurogenesis in a rat model of binge alcohol exposure during the brain growth spurt

Exposure to alcohol during the brain growth spurt results in impaired cognition and learning in adulthood. This impairment is accompanied by permanent structural changes in the hippocampal formation. Exercise improves performance on hippocampal-dependent learning and memory tasks and increases adult neurogenesis in the rat hippocampal dentate gyrus. The present study examined the effects of wheel running during adolescence on dentate gyrus cell proliferation and neurogenesis after postnatal binge-like alcohol exposure. On postnatal days (PD) 4-9, pups were either intubated with alcohol in a binge-like manner, sham intubated, or reared normally. On PD30-42, all animals were randomly assigned to two adolescent conditions: wheel running or inactive control. Animals were injected with BrdU every day between PD32 and PD42 and perfused on PD42 or PD72. In inactive control animals at both PD42 and PD72, cell proliferation and neurogenesis did not differ between postnatal treatment groups. Wheel running significantly increased the number of BrdU-labeled cells on PD42 in all three postnatal treatments. On PD72, only the normal controls showed significant increases in survival of newly generated cells resulting from the wheel running. These results indicate that adolescent wheel running can induce comparable increases in cell proliferation and neurogenesis in alcohol-exposed and control rats, but the long-term survival of those newly generated cells is impaired relative normal controls. Exercise may provide a means to stimulate neurogenesis, with implications for amelioration of hippocampal-dependent learning impairments associated with alcohol exposure. However, benefits requiring long-lasting survival of the newly generated cells will depend on identifying ways to promote survival.

Chronic but not acute foot-shock stress leads to temporary suppression of cell proliferation in rat hippocampus

Stressful experiences, especially when prolonged and severe are associated with psychopathology and impaired neuronal plasticity. Among other effects on the brain, stress has been shown to negatively regulate hippocampal neurogenesis, and this effect is considered to be exerted via glucocorticoids. Here, we sought to determine the temporal dynamics of changes in hippocampal neurogenesis after acute and chronic exposure to foot-shock stress. Rats subjected to a foot-shock procedure showed strong activation of the hypothalamic-pituitary-adrenal (HPA) axis, even after exposure to daily stress for 3 weeks. Despite a robust release of corticosterone, acute foot-shock stress did not affect the rate of hippocampal cell proliferation. In contrast, exposure to foot-shock stress daily for 3 weeks led to reduced cell proliferation 2 hours after the stress procedure. Interestingly, this stress-induced effect did not persist and was no longer detected 24 hours later. Also, while chronic foot-shock stress had no impact on survival of hippocampal cells that were born before the stress procedure, it led to a decreased number of doublecortin-positive granule neurons that were born during the chronic stress period. Thus, whereas a strong activation of the HPA axis during acute foot-shock stress is not sufficient to reduce hippocampal cell proliferation, repeated exposure to stressful stimuli for prolonged period of time ultimately results in dysregulated neurogenesis. In sum, this study supports the notion that chronic stress may lead to cumulative changes in the brain that are not seen after acute stress. Such changes may indicate compromised brain plasticity and increased vulnerability to neuropathology.