Sunday, March 2, 2008

Exercise and estrogen

Lady rats discovered that exercise plus estrogen was the magic formula for keeping their memory for maze-running intact. This interaction of estrogen and physical activity on the cells of the hippocampus which is the memory center of the brain may be important for humans as well.

Brain-derived neurotrophic factor (BDNF) is a molecule recognized by neuroscientists for its role in nerve cell growth and repair. In particular, BDNF promotes the growth of dendrites or those little tree-branch-like projections off a nerve cell body that hook that cell up with its neighbors. The more those neurons connect one to another, the easier the flow of important information such as the next word and the next word in the sentence that you are speaking.

Animal studies suggest that in the presence of estrogen, happy neurons bristle with dendrites. And lots of dendrites in the hippocampus and the frontal lobe of your brain promotes, perhaps, the fluent flow of speech. Without estrogen, dendrites drop off neurons like the broken teeth of an old comb. Those left out of estrogen and low on dendrites may be left dazed and confused in the kitchen, wondering for what they came.

Back to our California rats. While physical activity increased their hippocampal BDNF, this exercise effect was reduced by a loss of estrogen in a time-dependent fashion. In other words, the longer the rats went without estrogen, the less brain benefits were derived from working out on the old exercise wheel. By the seventh estrogen-free week, exercise affected BDNF levels not at all. What's even worse, voluntary activity levels dropped off as well; those rats who were out of estrogen were disinclined to bustle about their cages for the sheer joy of mousy bustling.

Estrogen replacement then restored the rodents' BDNF back to normal levels. And hopping back on the workout wheel, in combination with long-term estrogen use, increased BDNF the most of all.

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