neurosecretion

neurosecretion [¦nu̇r·ō·si′krē·shən]

(neuroscience)

The synthesis and release of hormones by nerve cells.

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Neurosecretion

The synthesis and release of hormones by neurons. Such neurons are called neurosecretory cells, and their products are often called neurohormones. Like conventional (that is, nonglandular or ordinary) neurons, neurosecretory cells are able to receive signals from other neurons. But unlike ordinary neurons that have cell-to-cell communication over short distances at synapses, neurosecretory cells release their product into an extracellular space that may be at some distance from the target cells. In an organism with a circulatory system, the neurohormones are typically sent by the vascular route to their target, whereas in lower invertebrates that lack an organized circulatory system the neurohormones apparently simply diffuse from the release site to the target. It is now clear that the nervous and endocrine systems interact in many ways, as in the suckling reflex of mammals (where the hormone oxytocin, a neurohormone, elicits milk ejection and is reflexly released in response to nerve impulses generated by stimulation of the nipples), and neurosecretory cells form a major link between them. See Endocrine system (invertebrate), Endocrine system (vertebrate)

It has been shown that peptides or low-molecular-weight proteins as well as amines, such as octopamine and dopamine, are released from neurosecretory cells into the circulatory systems of various animals, where they function as neurohormones. In classical neurosecretory cells, the secreted material is synthesized in the cell body by the rough-surfaced endoplasmic reticulum and subsequently packaged in the form of membrane-bounded granules by the Golgi apparatus, and is then typically transported along the axon to the axonal terminals, where it is stored until released. The release of neurohormones from axonal terminals into an extracellular space is triggered when the electrical activity (action potential) that is propagated by the axon enters the neurosecretory terminals. Calcium ions are essential for neurohormone release. See Biopotentials and ionic currents, Endoplasmic reticulum, Golgi apparatus

Neurohormones have a wide variety of functions. The role of the vertebrate hypothalamo-neurohypophysial system has been especially well elucidated. The pars nervosa is the site of release of vasopressin (also called the antidiuretic hormone) and oxytocin, and the median eminence is the release site for several hypothalamic neurohormones that regulate the adenohypophysis, the nonneural portion of the pituitary gland. See Adenohypophysis hormone, Nervous system (vertebrate), Neurohypophysis hormone, Pituitary gland