NEUROENDOCRINE CORRELATES OF THE AGING BRAIN IN HUMANS

Physiological brain aging is characterized by important biochemical an d structural changes and by the unbalance among the different neurotra nsmitters and neuromodulators. The study of the circadian organization of neuroendocrine functions may be considered a clinically reliable t ool to investigate the changes of the CNS and particularly of the limb ic-hypothalamic system occurring in aged people. The circadian rhythms of plasma melatonin, ACTH and cortisol and of oral temperature were s tudied in 16 clinically healthy women aged 66-90 years and in II young controls aged 20-30. In addition, the effect of dexamethasone on the plasma cortisol circadian rhythm and the cortisol response to Synacthe n pulse intravenous injection were evaluated. Ah subjects were studied as inpatients, with the same synchronization to the hospital life sch edule. When compared with young controls, elderly subjects exhibited a reduction of the mean level and of the amplitude of the circadian rhy thm of oral temperature, an increase of the mean level of ACTH and cor tisol rhythms and a selective impairment of melatonin nocturnal secret ion. Furthermore, elderly subjects showed a reduced sensitivity to the dexamethasone suppression test, by comparison to young controls. Thes e changes were age-related and they may depend either on CNS modificat ion or on alterations of the hormonal metabolic clearance.