The hypothalamus is composed of numerous nerve cells, which are arranged into six nuclear groups:
1. The preoptic region lies above and anterior to the optic chiasm and below the anterior commissure. It contains the medial and lateral preoptic areas.
2. The anterior group of nuclei, or rostral or supraoptic middle region, lies above the optic chiasm and is continuous anteriorly with the preoptic region.
3. The middle group, or tuberal or infundibular middle region, occupies the middle portion of the tuber cinereum. It is composed of the dorsomedial hypothalamic nucleus, the ventromedial hypothalamic nucleus, the dorsal hypothalamic area, the posterior hypothalamic area, and the perifornical area.
4. The lateral group, or region, occupies the lateral part of the tuber cinereum and includes both the lateral hypothalamic area and the nuclei tuberis lateralis.
5. The posterior group, or caudal or mammillary region, includes the premammillary area, the supramammillary area, and the mammillary bodies, containing the medial and lateral mammillary nuclei and the nucleus intercalatus.
6. The periventricular region contains many cellular masses that form the substantia grisea centralis. Included in this area are the nucleus periventricularis preopticus and the nucleus periventricularis arcuatus.
Under control of the hypothalamus are body temperature regulation; basal metabolism; water, glucose, and fat metabolism; cardiovascular regulation including adjustment of the blood pressure and circulation; control of respiration; regulation of bladder functions; influence over sexual activity; and endocrine correlation in general. Vasopressin and oxytonin originate in the neurohypophysis, the supraoptic and paraventricular nuclei. Corticotropin releasing factor originates mainly from the paraventricular nucleus. Gonadotropin-releasing hormone is produced in the arcuate nucleus, as is prolactin-releasing factor. Growth hormone releasing factor and somatostatin (inhibits release of growth hormone) are synthesized in the posterior arcuate, ventromedian, premammillary, periventricular, and paraventricular parts of the hypothalamus. Thyrotropin-releasing factor is produced by many hypothalamic nuclei, except for those in its posterior portion.