Neurohormone

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A neurohormone is any hormone produced and released by neuroendocrine cells (also called neurosecretory cells) into the blood. [1] [2] By definition of being hormones, they are secreted into the circulation for systemic effect, but they can also have a role of neurotransmitter or other roles such as autocrine (self) or paracrine (local) messenger. [3]

Contents

The hypothalamus releasing hormones are neurohypophysial hormones in specialized hypothalamic neurons which extend to the median eminence and posterior pituitary. The adrenal medulla produces adrenomedullary hormones in chromaffin cells, cells which are very similar in structure to post-synaptic sympathetic neurons, even though they are not neurons they are derivatives of the neural crest. [4]

Enterochromaffin and enterochromaffin-like cells, both being enteroendocrine cells, are also considered neuroendocrine cells due to their structural and functional similarity to chromaffin cells, although they are not derivatives of the neural crest. [5] Other neuroendocrine cells are scattered throughout the body. Neurohormone are released by neurosecretory cells

Releasing hormones

Releasing hormones also known as hypophysiotropic or hypothalamic hormones are synthesized by different kinds of specialized neurons in the hypothalamus. They are then transported along neuronal axons to their axon terminals forming the bulk of the median eminence, where they are stored and released into the hypophyseal portal system. They then rapidly reach the anterior pituitary where they exert their hormonal action. The residual hormones pass into the systemic circulation where they are diluted, degraded and have comparatively little effects. The synthesis, control, and release of those hormones is co-regulated by hormonal, local and synaptic signals (neurotransmitters). [6] [7] The neurons secreting various hormones have been found to discharge impulses in burst, causing a pulsatile release which is more efficient than a continuous release. [8] Hypophysiotropic hormones include:

Neurohypophysial hormones

Neurohypophysial hormones are synthesized in the magnocellular secretory neurons of the hypothalamus. They are then transported along neuronal axons within the infundibular stalk to their axon terminals forming the pars nervosa of the posterior pituitary, where they are stored and released into the systemic circulation. The synthesis, control, and release of those hormones is co-regulated by hormonal, local and synaptic signals. [9] Neurohypophysial hormones include:

This is through this pathway that the vast majority of oxytocin and vasopressin hormones reach the systemic circulation.

Adrenomedullary hormones

Adrenomedullary hormones are catecholamines secreted from the adrenal medulla by chromaffin cells, neurosecretory cells connected to the central nervous system. [10] The synthesis, storage (in chromaffin cells) and release of catecholamines is co-regulated by synaptic input from their respective pre-synaptic sympathetic neurons, as well as hormonal and local inputs. [11] [12] The adrenomedullary hormones are:

Enteric neurohormones

Enterochromaffin cells in the epithelia lining the lumen of the digestive tract secrete serotonin, while enterochromaffin-like cells at the stomach glands secrete histamine. Their synthesis, storage, and release of hormones is co-regulated by hormonal, local and nervous inputs. [13] [14] [15] [16] [17]

See also

Related Research Articles

<span class="mw-page-title-main">Adrenal gland</span> Endocrine gland

The adrenal glands are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which produces steroid hormones and an inner medulla. The adrenal cortex itself is divided into three main zones: the zona glomerulosa, the zona fasciculata and the zona reticularis.

<span class="mw-page-title-main">Endocrine system</span> Hormone-producing glands of a body

The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems. In humans, the major endocrine glands are the thyroid gland, parathyroid gland, pituitary gland, pineal gland, the testes (male), ovaries (female), and the adrenal glands. The hypothalamus, pancreas, and thymus also function as endocrine glands, among other functions. Other organs, such as the kidneys, also have roles within the endocrine system by secreting certain hormones. The study of the endocrine system and its disorders is known as endocrinology.

<span class="mw-page-title-main">Pituitary gland</span> Endocrine gland at the base of the brain

In vertebrate anatomy, the pituitary gland is an endocrine gland. In humans, it is about the size of a chickpea and weighs, on average, 0.5 grams (0.018 oz). It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypophysis rests upon the hypophyseal fossa of the sphenoid bone in the center of the middle cranial fossa and is surrounded by a small bony cavity covered by a dural fold.

<span class="mw-page-title-main">Hypothalamus</span> Area of the brain below the thalamus

The hypothalamus is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus is located below the thalamus and is part of the limbic system. In the terminology of neuroanatomy, it forms the ventral part of the diencephalon. All vertebrate brains contain a hypothalamus. In humans, it is the size of an almond.

<span class="mw-page-title-main">Catecholamine</span> Class of chemical compounds

A catecholamine is a monoamine neurotransmitter, an organic compound that has a catechol and a side-chain amine.

<span class="mw-page-title-main">Adrenal medulla</span> Central part of the adrenal gland

The adrenal medulla is part of the adrenal gland. It is located at the center of the gland, being surrounded by the adrenal cortex. It is the innermost part of the adrenal gland, consisting of chromaffin cells that secrete catecholamines, including epinephrine (adrenaline), norepinephrine (noradrenaline), and a small amount of dopamine, in response to stimulation by sympathetic preganglionic neurons.

<span class="mw-page-title-main">Somatostatin</span> Peptide hormone that regulates the endocrine system

Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones. Somatostatin inhibits insulin and glucagon secretion.

<span class="mw-page-title-main">Posterior pituitary</span> Posterior lobe of the pituitary gland

The posterior pituitary is the posterior lobe of the pituitary gland which is part of the endocrine system. The posterior pituitary is not glandular as is the anterior pituitary. Instead, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary, and serve as a site for the secretion of neurohypophysial hormones directly into the blood. The hypothalamic–neurohypophyseal system is composed of the hypothalamus, posterior pituitary, and these axonal projections.

<span class="mw-page-title-main">Chromaffin cell</span> Neuroendocrine cells found in adrenal medulla in mammals

Chromaffin cells, also called pheochromocytes, are neuroendocrine cells found mostly in the medulla of the adrenal glands in mammals. These cells serve a variety of functions such as serving as a response to stress, monitoring carbon dioxide and oxygen concentrations in the body, maintenance of respiration and the regulation of blood pressure. They are in close proximity to pre-synaptic sympathetic ganglia of the sympathetic nervous system, with which they communicate, and structurally they are similar to post-synaptic sympathetic neurons. In order to activate chromaffin cells, the splanchnic nerve of the sympathetic nervous system releases acetylcholine, which then binds to nicotinic acetylcholine receptors on the adrenal medulla. This causes the release of catecholamines. The chromaffin cells release catecholamines: ~80% of adrenaline (epinephrine) and ~20% of noradrenaline (norepinephrine) into systemic circulation for systemic effects on multiple organs, and can also send paracrine signals. Hence they are called neuroendocrine cells.

<span class="mw-page-title-main">Supraoptic nucleus</span> ADH secreting nucleus of the hypothalamus.

The supraoptic nucleus (SON) is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, the SON contains about 3,000 neurons.

<span class="mw-page-title-main">Paraventricular nucleus of hypothalamus</span>

The paraventricular nucleus is a nucleus in the hypothalamus. Anatomically, it is adjacent to the third ventricle and many of its neurons project to the posterior pituitary. These projecting neurons secrete oxytocin and a smaller amount of vasopressin, otherwise the nucleus also secretes corticotropin-releasing hormone (CRH) and thyrotropin-releasing hormone (TRH). CRH and TRH are secreted into the hypophyseal portal system and act on different targets neurons in the anterior pituitary. PVN is thought to mediate many diverse functions through these different hormones, including osmoregulation, appetite, and the response of the body to stress.

Magnocellular neurosecretory cells are large neuroendocrine cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus. They are also found in smaller numbers in accessory cell groups between these two nuclei, the largest one being the circular nucleus. There are two types of magnocellular neurosecretory cells, oxytocin-producing cells and vasopressin-producing cells, but a small number can produce both hormones. These cells are neuroendocrine neurons, are electrically excitable, and generate action potentials in response to afferent stimulation. Vasopressin is produced from the vasopressin-producing cells via the AVP gene, a molecular output of circadian pathways.

<span class="mw-page-title-main">Arcuate nucleus</span>

The arcuate nucleus of the hypothalamus is an aggregation of neurons in the mediobasal hypothalamus, adjacent to the third ventricle and the median eminence. The arcuate nucleus includes several important and diverse populations of neurons that help mediate different neuroendocrine and physiological functions, including neuroendocrine neurons, centrally projecting neurons, and astrocytes. The populations of neurons found in the arcuate nucleus are based on the hormones they secrete or interact with and are responsible for hypothalamic function, such as regulating hormones released from the pituitary gland or secreting their own hormones. Neurons in this region are also responsible for integrating information and providing inputs to other nuclei in the hypothalamus or inputs to areas outside this region of the brain. These neurons, generated from the ventral part of the periventricular epithelium during embryonic development, locate dorsally in the hypothalamus, becoming part of the ventromedial hypothalamic region. The function of the arcuate nucleus relies on its diversity of neurons, but its central role is involved in homeostasis. The arcuate nucleus provides many physiological roles involved in feeding, metabolism, fertility, and cardiovascular regulation.

Neuroendocrine cells are cells that receive neuronal input and, as a consequence of this input, release messenger molecules (hormones) into the blood. In this way they bring about an integration between the nervous system and the endocrine system, a process known as neuroendocrine integration. An example of a neuroendocrine cell is a cell of the adrenal medulla, which releases adrenaline to the blood. The adrenal medullary cells are controlled by the sympathetic division of the autonomic nervous system. These cells are modified postganglionic neurons. Autonomic nerve fibers lead directly to them from the central nervous system. The adrenal medullary hormones are kept in vesicles much in the same way neurotransmitters are kept in neuronal vesicles. Hormonal effects can last up to ten times longer than those of neurotransmitters. Sympathetic nerve fiber impulses stimulate the release of adrenal medullary hormones. In this way the sympathetic division of the autonomic nervous system and the medullary secretions function together.

<span class="mw-page-title-main">Enterochromaffin-like cell</span>

Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell found in the gastric glands of the gastric mucosa beneath the epithelium, in particular in the vicinity of parietal cells, that aid in the production of gastric acid via the release of histamine. They are also considered a type of enteroendocrine cell.

<span class="mw-page-title-main">Enterochromaffin cell</span> Cell type

Enterochromaffin (EC) cells are a type of enteroendocrine cell, and neuroendocrine cell. They reside alongside the epithelium lining the lumen of the digestive tract and play a crucial role in gastrointestinal regulation, particularly intestinal motility and secretion. They were discovered by Nikolai Kulchitsky.

Neuroendocrinology is the branch of biology which studies the interaction between the nervous system and the endocrine system; i.e. how the brain regulates the hormonal activity in the body. The nervous and endocrine systems often act together in a process called neuroendocrine integration, to regulate the physiological processes of the human body. Neuroendocrinology arose from the recognition that the brain, especially the hypothalamus, controls secretion of pituitary gland hormones, and has subsequently expanded to investigate numerous interconnections of the endocrine and nervous systems.

<span class="mw-page-title-main">Paraganglion</span>

A paraganglion is a group of non-neuronal cells derived of the neural crest. They are named for being generally in close proximity to sympathetic ganglia. They are essentially of two types: (1) chromaffin or sympathetic paraganglia made of chromaffin cells and (2) nonchromaffin or parasympathetic ganglia made of glomus cells. They are neuroendocrine cells, the former with primary endocrine functions and the latter with primary chemoreceptor functions.

<span class="mw-page-title-main">Neurophysin II</span>

Neurophysin II is a carrier protein with a size of 19,687.3 Da and is made up of a dimer of two virtually identical chains of amino acids. Neurophysin II is a cleavage product of the AVP gene. It is a neurohypophysial hormone that is transported in vesicles with vasopressin, the other cleavage product, along axons, from magnocellular neurons of the hypothalamus to the posterior lobe of the pituitary. Although it is stored in neurosecretory granules with vasopressin and released with vasopressin into the bloodstream, its biological action is unclear. Neurophysin II is also known as a stimulator of prolactin secretion.

Parvocellular neurosecretory cells are small neurons that produce hypothalamic releasing and inhibiting hormones. The cell bodies of these neurons are located in various nuclei of the hypothalamus or in closely related areas of the basal brain, mainly in the medial zone of the hypothalamus. All or most of the axons of the parvocellular neurosecretory cells project to the median eminence, at the base of the brain, where their nerve terminals release the hypothalamic hormones. These hormones are then immediately absorbed into the blood vessels of the hypothalamo-pituitary portal system, which carry them to the anterior pituitary gland, where they regulate the secretion of hormones into the systemic circulation.

References

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  2. ↑ Nelson. 2005 An Introduction To Behavioral Endocrinology, Third Edition
  3. ↑ Purves et al. p. 714.
  4. ↑ Unsicker K, Huber K, Schütz G, Kalcheim C (Jun–Jul 2005). "The chromaffin cell and its development". Neurochemical Research. 30 (6–7): 921–5. doi:10.1007/s11064-005-6966-5. PMID   16187226.
  5. ↑ Andrew A (June 1974). "Further evidence that enterochromaffin cells are not derived from the neural crest". Journal of Embryology and Experimental Morphology. 31 (3): 589–98. PMID   4448939.
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  7. ↑ Nillni EA (April 2010). "Regulation of the hypothalamic thyrotropin releasing hormone (TRH) neuron by neuronal and peripheral inputs". Frontiers in Neuroendocrinology. 31 (2): 134–56. doi:10.1016/j.yfrne.2010.01.001. PMC   2849853 . PMID   20074584.
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  9. ↑ Burbach JP, Luckman SM, Murphy D, Gainer H (July 2001). "Gene regulation in the magnocellular hypothalamo-neurohypophysial system". Physiological Reviews. 81 (3): 1197–267. doi:10.1152/physrev.2001.81.3.1197. PMID   11427695.
  10. ↑ Chung KF, Sicard F, Vukicevic V, Hermann A, Storch A, Huttner WB, Bornstein SR, Ehrhart-Bornstein M (October 2009). "Isolation of neural crest derived chromaffin progenitors from adult adrenal medulla". Stem Cells. 27 (10): 2602–13. doi: 10.1002/stem.180 . PMID   19609938.
  11. ↑ Gasman S, Chasserot-Golaz S, Bader MF, Vitale N (October 2003). "Regulation of exocytosis in adrenal chromaffin cells: focus on ARF and Rho GTPases". Cellular Signalling. 15 (10): 893–9. doi:10.1016/S0898-6568(03)00052-4. PMID   12873702.
  12. ↑ Bornstein SR, Ehrhart-Bornstein M (December 1992). "Ultrastructural evidence for a paracrine regulation of the rat adrenal cortex mediated by the local release of catecholamines from chromaffin cells". Endocrinology. 131 (6): 3126–8. doi:10.1210/endo.131.6.1446648. PMID   1446648.
  13. ↑ Prinz C, Zanner R, Gerhard M, Mahr S, Neumayer N, Höhne-Zell B, Gratzl M (November 1999). "The mechanism of histamine secretion from gastric enterochromaffin-like cells". The American Journal of Physiology. 277 (5 Pt 1): C845-55. PMID   10564076.
  14. ↑ Rhee SH, Pothoulakis C, Mayer EA (May 2009). "Principles and clinical implications of the brain-gut-enteric microbiota axis". Nature Reviews. Gastroenterology & Hepatology. 6 (5): 306–14. doi:10.1038/nrgastro.2009.35. PMC   3817714 . PMID   19404271.
  15. ↑ Haas HL, Sergeeva OA, Selbach O (July 2008). "Histamine in the nervous system". Physiological Reviews. 88 (3): 1183–241. doi:10.1152/physrev.00043.2007. PMID   18626069.
  16. ↑ Rodriguez-Diaz R, Dando R, Jacques-Silva MC, Fachado A, Molina J, Abdulreda MH, Ricordi C, Roper SD, Berggren PO, Caicedo A (June 2011). "Alpha cells secrete acetylcholine as a non-neuronal paracrine signal priming beta cell function in humans". Nature Medicine. 17 (7): 888–92. doi:10.1038/nm.2371. PMC   3132226 . PMID   21685896.
  17. ↑ Sandor A, Kidd M, Lawton GP, Miu K, Tang LH, Modlin IM (April 1996). "Neurohormonal modulation of rat enterochromaffin-like cell histamine secretion". Gastroenterology. 110 (4): 1084–92. doi: 10.1053/gast.1996.v110.pm8612997 . PMID   8612997.
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