The<unk>  <unk>  is an ovoid, densely packed cluster of large cells located in the medial preoptic area (POA) of the hypothalamus which is believed to be related to sexual behavior in animals. Thus far, for all species of mammals investigated, the<unk>  has been repeatedly found to be considerably larger in males than in females. In humans, the volume of the<unk>  has been found to be 2.2 times as large in males as in females and to contain 2.1 times as many cells. The human<unk>  is elongated in females and more spherical in males. No sex differences have been observed in the human<unk>  in either cell density or mean diameter of the cell nuclei. The volume and cell number of the human<unk>  considerably decreases with age, although the decrease in cell number is both sex and age-specific. In males, a substantial decrease in the cell number of the human<unk>  was observed between the age of 50–60 years. Cell death was more common in females than males, especially among those older than 70 years of age. The<unk>  cell number in females can drop to 10-15% of that found in early childhood.<unk>  and its homologues exist widely in human, mammal, and some other animal brains, including: * the third interstitial nucleus of the anterior hypothalamus (INAH3) in humans; * ovine<unk>  (oSDN) in the medial preoptic area/anterior hypothalamus (MPOA/AH) in sheep; *<unk>  in the preoptic area <unk> -POA) in rats; * anterior hypothalamic nucleus (AHdc) in macaques; * specific area in medial preoptic nucleus (POM) in quails; etc.
Sexually dimorphic nucleus
Preoptic anterior hypothalamus
Allothalamus
Isothalamus
Olfactory trigone
Ciliospinal center
Gigantocellular reticular nucleus
Reticulotegmental nucleus