An urge to explain the incomprehensible: Geoffrey Harris and the discovery of the neural control of the pituitary gland.

Geoffrey Harris is responsible for our view that the brain controls the endocrine system by an exquisitely regulated pattern of synthesis and release of individual members of a family of peptide hormones. These hormones are carried through a portal vascular system that passes from the hypothalamus to the pituitary gland, where they selectively regulate the secretion of the six anterior pituitary hormones. This family of hypothalamic hormones is highly conserved in all vertebrates, including humans. They are essential for all aspects of reproduction--courtship, mating, pregnancy and young rearing--and they are responsible for the seasonal regulation of breeding. The hypothalamic control mechanism for reproduction is sexually dimorphic, with a basic female pattern that becomes masculinized under the influence of specific steroid hormones acting during development. Other members of the hypothalamic hormone family specifically regulate the secretion of pituitary growth hormone and the anterior pituitary hormones controlling the functions of the thyroid and adrenal glands. The secretion of the hypothalamic hormones is itself regulated by the feedback of the target gland hormones (such as estrogen and progesterone), which concurrently act on the brain to elicit appropriate behavior patterns. The hypothalamo-hypophysial axis plays a crucial role in the struggle for the survival of the species. By bringing the endocrine system under the control of the brain, it allows access to external environmental inputs, learned behavior patterns, and the whole of the central integrative machinery needed for the bodily functions to be sensitively and optimally adapted to the ever-changing challenges and opportunities in the outside world.