GRUMPY old people may be bad-tempered because their brains react differently to chronic stress. At least that鈥檚 what happens to elderly rats.
Elderly humans are more vulnerable to stress than their youthful counterparts. 鈥淭here is more low-level anxiety and depression,鈥� says of the University of Queensland in Brisbane, Australia.
To investigate why, Hirotaka Shoji of the in Obu, Japan, put 3-month-old and 24-month-old rats under stress by placing them inside a wire-mesh container for 1 hour every day for two weeks. Before this treatment began, the two sets of rats had similar levels of the stress hormone, corticosterone. All the rats had higher levels of the hormone after two weeks, but the old rats had significantly more. The old rats also showed increased activity in areas of the brain associated with anxiety and decreased activity in regions linked with controlling emotions (Behavioural Brain Research, ).
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Shoji suggests that ageing may reduce the brain鈥檚 ability to damp down the release of corticosterone in response to repeated stress. When another group of rats were put in the cage just once, for an hour, stress hormone levels were similar in old and young rats, suggesting that ageing increases vulnerability to repeated stress rather than one-off episodes.
鈥淭he brain鈥檚 ability to damp down the release of stress hormones may be reduced with age鈥�
of the Auckland University of Technology, New Zealand, says it is difficult to compare lab rats with humans. Physical and mental exercise can protect the human brain, but lab rats don鈥檛 have equivalent stimuli, he says.
