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Thus the brain, and indeed the entire central nervous system, consists of an extraordinary network of neurons interconnected by neurotransmitters. The secretion of specific neurotransmitters, modified by neuromodulators, lends an organized, directed function to the overall system. These neural connections extend upward from the hypothalamus into other key areas, including the cerebral cortex. The result is that intellectual and functional activities as well as external influences, including stresses, can be funneled into the hypothalamus and thence to the endocrine system, from which they may exert effects on the body.

In addition to secreting neurotransmitters and neuromodulators, the hypothalamus synthesizes and secretes a number of neurohormones. The neurons secreting neurohormones are true endocrine (neurohemal) cells in the classical sense since secretory granules containing neurohormones travel from the cell body through the axon to be extruded, where they enter directly a capillary network, thence to be transported through the hypophyseal-portal circulation to the anterior pituitary gland.

Finally, the neurohypophysis, or posterior lobe of the pituitary gland, provides the classical example of neurohormonal activity. The secretory products, mainly vasopressin and oxytocin, are extruded into a capillary network, which feeds directly into the general circulation.

The existence of hormones of the hypothalamus was predicted well before they were detected and chemically characterized, and they have been studied intensively by many investigators. Two groups of American investigators, led by Andrew Schally and Roger Guillemin, respectively, shared the Nobel Prize for Physiology or Medicine for 1977 for their research on pituitary hormones.

These neurohormones are known as releasing hormones because the major function generally is to stimulate the secretion of hormones originating in the anterior pituitary gland. They consist of simple peptides (chains of amino acids) ranging in size from only three amino acids (thyrotropin-releasing hormone) to 44 amino acids (growth hormone-releasing hormone).
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