Neurohormone

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A neurohormone is a hormone that is released from neurons to the surrounding tissue and reaches its target cells in the hemolymph or bloodstream . The nerve cell secreting the messenger substance is also called the neurosecretory cell and is understood as an element of a neurohormonal system .

Neurohormones, for example, in humans of neurons in several key areas of the hypothalamus formed into vesicles packed, to the ends of their neurites transported , there kept on hand and on certain signals via exocytosis released. The hormones oxytocin and vasopressin get into the blood from endings in the neurohypophysis (posterior pituitary lobe, HHL) as a neurohemal organ .

In addition, it has been known since 1969 that neurites of other hypothalamic neurons end in the eminentia mediana , where they release neurohormones into the blood of venous portal vessels of the pituitary stalk . In this way, they quickly reach target cells in the adenohypophysis (anterior pituitary lobes, HVL) and can influence the release of various other (sometimes glandotropic ) hormones there. These neurohormones from the hypothalamus include thyrotropin-RH (TRH), corticotropin-RH (CRH), gonadotropin-RH (GnRH) and somatotropin-RH (SRH) as releasing hormones (RH) or liberins with a promoting effect ; as inhibiting hormones (IH) or statins with an inhibitory effect, somatostatin (SIH) and prolactostatin (PIH) are included. The latter is the biogenic amine dopamine , the rest are peptide hormones .

The hormone melatonin , which is formed in the epiphysis ( pineal gland ) of the epithalamus , is also commonly counted among the neurohormones. In 1975 another group of neurohormonal messenger substances was found, the enkephalins .

Like classic hormones, neurohormones can reach their target cells via circulating hemolymph or blood fluid transported in the body by nerve cells. In this case, the neurosecretory cells are often addressed as neuroendocrinically active neurons. In addition, messenger substances that are secreted into the tissue fluid by a nerve cell and thus reach target cells in the vicinity are also referred to as paracrine acting neurohormones .

In both cases, the term neurohormone is used for a situation of signal transmission that differs from that of excitation transmission at chemical synapses , where a nerve cell releases a messenger substance as a neurotransmitter or neuromodulator into the synaptic gap , to a postsynaptically assigned cell. The decisive factor for the use of the term is not the type of messenger substance, but where it is delivered.

There are therefore also messenger substances in the body that are used both as neurohormones and in other functions. Norepinephrine, for example, is excreted by both the adrenal gland (glandular hormone) and sympathetic nerves (neurohormone). There are also substances that function both as neurohormones and as neurotransmitters, for example dopamine or somatostatin.

See also

Individual evidence

  1. ^ A b Berta Scharrer : Neurohumors and Neurohormones: Definitions and Terminology. In: Journal of Neuro-Visceral Relations. Supplementum IX. Springer-Verlag, Vienna 1969, pp. 1 and 2 , ff. Here online
  2. ^ A b c d Josef Dudel, Randolf Menzel, Robert F. Schmidt (ed.): Neuroscience: From Molecule to Cognition. 2nd Edition. Springer-Verlag, 2013, ISBN 978-3-642-56497-0 , p. 243 ff; here online
  3. ↑ a b c Stefan Silbernagl , Agamemnon Despopoulos : Pocket Atlas Physiology. 8th edition. Thieme Verlag, 2012, ISBN 978-3-13-567708-8 , pp. 284 and 294, online here
  4. ↑ a b Entry Neurohormones in Encyclopædia Britannica Online Version. Retrieved June 4, 2014.
  5. ↑ Josef Köhrle: Basics of the paracrine, autocrine and intracrine regulation of endocrine organs. In Ganten / Ruckpaul (ed.): Molecular medical principles of paracrine and autocrine regulation disorders. Springer 2006, p. 6f ; here as PDF
  6. ^ A b Robert F. Schmidt, Gerhard Thews: Physiologie des Menschen. 23rd edition. Springer-Verlag, 2013, ISBN 978-3-662-09340-5 , pp. 393 and 727, online here
  7. ^ Henryk Nowakowski: Tissue and neurohormones: Physiology of the melanophoric hormone. Springer-Verlag, 1962, ISBN 978-3-642-86860-3 , p. 14, online here
  8. ↑ Peter Karlson, Detlef Doenecke (Ed.): Biochemistry and Pathobiochemistry. 15th edition. Thieme Verlag, 2005, ISBN 978-3-133-57815-8 , p. 539, online here