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a physiologically active substance that is produced by special neurons—the neurosecretory cells.
Like a mediator substance (chemical transmitter), a neurohormone is released by nerve endings, but in contrast to the first, a neurohormone is secreted into the blood or tissue fluid. Such secretion into the body fluids is characteristic of hormones. Neurohormones, for example, vasopressin, oxytocin, and the adenohypophysiotropic hormones, have been discovered in many vertebrates and in many invertebrates, including mollusks, worms, and arthropods. Chemically, the majority of neurohormones are peptides; some are catecholamines. Biosynthesis of peptide neurohormones occurs in the endoplasmic reticulum of the cell body of the neuron, The peptides are packaged in the Golgi complex and are subsequently transported along the axon to the nerve endings. In the mammalian brain the neurosecretory cells of the hypothalamus are a source of neurohormones. Neurohormones regulate the activity of the cells of some endocrine glands and influence the cells of other organs.