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Seventy years ago, C. M. McCay et al. discovered that reducing the amount of calories fed to rodents nearly doubled their life spans. The life extension varied for each species, but on average there was a 30–40% increase in life span in both mice and rats.[50] CR preserves a range of structural and functional parameters in aging rodents. For example, studies in female mice have shown that estrogen receptor-alpha declines in the aging pre-optic hypothalamus. The female mice that were given a calorically restricted diet during the majority of their lives maintained higher levels of ERα in the pre-optic hypothalamus than did their non–calorically restricted counterparts.[51] Studies in female mice have shown that both the Supraoptic nucleus (SON) and Paraventricular nucleus (PVN) lose about one-third of IGF-1R immunoreactivity with normal aging. Old calorically restricted mice lose higher numbers of IGF-1R non-immunoreactive cells while maintaining similar counts of IGF-1R immunoreactive cells in comparison to Old-Al mice. Consequently, Old-CR mice show a higher percentage of IGF-1R immunoreactive cells, reflecting increased hypothalamic sensitivity to IGF-1, in comparison to normally aging mice.[52][53] |
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