Activation and degeneration during aging: A morphometric study of the human hypothalamus

During the course of aging both activation and degenerative changes are fou nd in the human hypothalamus. Degeneration may start around middle-age in s ome neurotransmitter- or neuromodulator-containing neurons. For instance, a decreased number of vasoactive intestinal polypeptide (VIP) neurons was ob served in the suprachiasmatic nucleus (SCN) of middle-aged males. The norma l circadian fluctuations seen in the number of vasopressin (AVP) neurons in the SCN of young subjects diminished in subjects older than 50 years. More over, a sharp decline in cell number was found in the sexually dimorphic nu cleus (SDN) after 50 years in males. On the other hand, many hypothalamic s ystems remain perfectly intact during aging like the oxytocin (OXT) neurons in the paraventricular nucleus (PVN). The AVP neurons in the PVN are activ ated during aging as appears from their increasing cell number. Also the co rticotrophin-releasing hormone (CRH) neurons of the PVN are activated in th e course of aging, as indicated by their increased number and their increas ed AVP coexpression. Part of the infundibular nucleus, the subventricular n ucleus, contains hypertrophic neurokinin B neurons in postmenopausal women. It can be concluded that a multitude of changes in the various hypothalami c nuclei may be the biological basis for many functional changes in aging, i.e., both endocrine and central alterations, and that only a minority of t he possible human hypothalamic changes have so far been studied. (C) 1999 W iley-Liss, Inc.