Modulation of brain aging correlates by long-term alterations of adrenal steroids and neurally-active peptides

Many mammalian cell systems deteriorate or cease functioning in vivo before the deterioration is necessitated by intrinsic cellular processes. There are circulating factors in plasma that can modulate the rate of age-dependent cellular deterioration of some systems. Some factor(s) essential to normal function may be lacking in plasma of aging animals or, alternatively, some factor(s) that accelerates age-related deterioration may become more effective in plasma of aged animals. Although the study of the long-term effects of adrenal steroids and neuropeptides is new, increasing evidence indicates that chronic exposure to steroid and peptide hormones can alter adult brain structure and function, or can modify the effects of aging on the brain. There is evidence that at least some of these effects may be receptor-mediated, or mediated by effects of neural activity. However, a substantial amount of additional research is required to elucidate the cellular mechanisms of the hormonal actions on brain structure and function.