Hormetic effects of repeated exposures to cold at young age on longevity, aging and resistance to heat or cold shocks in Drosophila melanogaster

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Abstract
Exposing young flies to hypergravity has hormetic effects on aging, longevity and resistance to heat stress. The present experiments tested whether cold shocks at young age could also have hormetic effects. Flies were cold-shocked at 0°C daily for 60 min during two periods of 5 days separated by 2 days, starting at 5 days of age. This cold stress increased longevity, resistance to a lethal heat stress or to cold up to 6 weeks of age, resistance to a non-lethal heat stress at middle age, and delayed behavioral aging. Cold and hypergravity exposure at young age have thus similar effects, excepting on resistance to cold stress, which is not increased after exposure to hypergravity. Mild heat stress has also been shown to slightly increase longevity and resistance to a lethal heat stress, but not to delay behavioral aging. Since there are thus at least two mild stresses with large hormetic effects at old age in flies, i.e. cold and hypergravity, hormetic effects in flies are not stress-specific. Therefore, it could be hypothetized that hormetic effects of mild stress on aging and longevity are a general phenomenon and that they could also be observed in other species such as rodents.