Neurosecretion

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Neurosecretion is the release of extracellular vesicles and particles from neurons, astrocytes, microglial and other cells of the central nervous system. These neurohormones, produced by neurosecretory cells, are normally secreted from nerve cells in the brain that then circulate into the blood. These neurohormones are similar to nonneural endocrine cells and glands in that they also regulate both endocrine and nonendocrine cells. Neurosecretion cells synthesize and package their product in vesicles and exocytose them at axon endings just as normal neurons do, but release their product farther from their target than normal neurons (which release their neurotransmitters short distances at synapses), typically releasing their neurohormones into the circulatory system to reach their distant targets. [1] [2]

Contents

Discovery

In 1928, Ernst Scharrer hypothesized that neurosecretory neurons in the hypothalamus of teleost fish, Phoxinus laevis, had secretory activity similar to that of endocrine gland cells. [3] As more became known about neurosecretory cells, the difference between the actions of nerve communication and endocrine hormone release become less clear. Like the average neuron, these cells conduct electrical impulses along the axon but unlike these neurons, neurosecretion produces neurohormones that are released into the body’s circulation. Combining the properties of the nervous and endocrine, these cells have the capacity to affect nerves through chemical messengers. [4] Neurosecretion is a broad area of study and must be further observed to be better understood.

Insects

Insects play a large role in what is known about neurosecretion. In simpler organisms neurosecretion mechanisms regulate the heart, the process of metamorphosis, and directly influences the development of the gonadal function. In more advanced organisms the gonadal function is manipulated by the intermediary endocrine processes. [5] Axons from neurosecretory cells trace to corpora cardiaca and corpora allata and produce and secrete a brain hormone which insect physiologists suspect is bound to a large carrier protein. Although the function is unknown, there are a multitude of these cells found in the ventral ganglia of the nerve cord. Neurosecretory cells, found in clusters in the medial and lateral parts of the brain, control corpora allata activity by producing juvenile hormone during the larval or nymphal instars, [6] the phase between periods of molting in insects. [7]

The production of this hormone inhibits the insect during the conversion to maturity and reactivating once the fully-grown adult is prepared for reproduction. The 3rd International Symposium on Neurosecretion at the University of Bristol discussed the intracellular structure of the neurosecretory cells and the migration path to the target organs or vascular fluid areas by neurosecretory granules. More is being discovered on the identification of granules in hormones and the linking of their development with the organism’s physiologic state. [5] Neurosecretion in Tasar Silkworm, Antheraea mylitta Drury was investigated by Tripathi, P N et al.,(1997)and they suggested the presence of multilobed corpora allata in this lepidopteran insect.

Related Research Articles

<span class="mw-page-title-main">Endocrinology</span> Branch of medicine dealing the endocrine system

Endocrinology is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. It is also concerned with the integration of developmental events proliferation, growth, and differentiation, and the psychological or behavioral activities of metabolism, growth and development, tissue function, sleep, digestion, respiration, excretion, mood, stress, lactation, movement, reproduction, and sensory perception caused by hormones. Specializations include behavioral endocrinology and comparative endocrinology.

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

The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems.

<span class="mw-page-title-main">Hormone</span> Biological signalling molecule

A hormone is a class of signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physiology and behavior. Hormones are required for the correct development of animals, plants and fungi. Due to the broad definition of a hormone, numerous kinds of molecules can be classified as hormones. Among the substances that can be considered hormones, are eicosanoids, steroids, amino acid derivatives, protein or peptides, and gases.

Tropic hormones are hormones that have other endocrine glands as their target. Most tropic hormones are produced and secreted by the anterior pituitary. The hypothalamus secretes tropic hormones that target the anterior pituitary, and the thyroid gland secretes thyroxine, which targets the hypothalamus and therefore can be considered a tropic hormone.

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

The anterior pituitary is a major organ of the endocrine system. The anterior pituitary is the glandular, anterior lobe that together with the makes up the pituitary gland (hypophysis) which, in humans, is located at the base of the brain, protruding off the bottom of the hypothalamus.

Juvenile hormones (JHs) are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. The first discovery of a JH was by Vincent Wigglesworth. JHs regulate development, reproduction, diapause, and polyphenisms.

<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">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 of hypothalamus is a nucleus in the hypothalamus, that lies next to the third ventricle. Many of its neurons project to the posterior pituitary where they secrete oxytocin, and a smaller amount of vasopressin. Other secretions are corticotropin-releasing hormone (CRH) and thyrotropin-releasing hormone (TRH). CRH and TRH are secreted into the hypophyseal portal system, and target different neurons in the anterior pituitary. Dysfunctions of the PVN can cause hypersomnia in mice. In humans, the dysfunction of the PVN and the other nuclei around it can lead to drowsiness for up to 20 hours per day. The PVN is thought to mediate many diverse functions through different hormones, including osmoregulation, appetite, wakefulness, 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 (hypothalamus)</span> Neuron cluster in the hypothalamus

The arcuate nucleus of the hypothalamus (ARH), or ARC, is also known as the infundibular nucleus to distinguish it from the arcuate nucleus of the medulla oblongata in the brainstem. The arcuate nucleus 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.

<span class="mw-page-title-main">Endocrine gland</span> Glands of the endocrine system that secrete hormones to blood

The endocrine system is a network of glands and organs located throughout the body. It is similar to the nervous system in that it plays a vital role in controlling and regulating many of the body's functions. Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testicles, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. The hypothalamus and pituitary glands are neuroendocrine organs.

A neurohormone is any hormone produced and released by neuroendocrine cells into the blood. 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.

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 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">Berta Scharrer</span> German-born American neuroendocrinologist

Berta Vogel Scharrer was an American scientist who helped to found the scientific discipline now known as neuroendocrinology.

Insect physiology includes the physiology and biochemistry of insect organ systems.

In insect physiology and anatomy, the corpus allatum is an endocrine gland that generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata can cause an immature larva to pupate at its next molt, resulting in a miniature adult. Similarly, transplantation of corpora allata from a young larva to a fully mature larva can greatly extend the larval stage, resulting in an equivalent to gigantism.

James "Jim" William Truman is an American chronobiologist known for his seminal research on circadian rhythms in silkmoth (Saturniidae) eclosion, particularly the restoration of rhythm and phase following brain transplantation. He is a professor emeritus at the University of Washington and a former senior fellow at Howard Hughes Medical Institution Janelia Research Campus.

References

  1. ↑ "Neurosecretion". Access Science from McGraw-Hill. Archived from the original on 17 June 2011. Retrieved 5 November 2010.
  2. ↑ "Neurosecretion". Biology-Online. Archived from the original on 19 July 2009. Retrieved 5 November 2010.
  3. ↑ Scharrer B (1977). "An Evolutionary Interpretation of the Phenomenon of Neurosecretion". Forty-seventh James Arthur Lecture on the Evolution of the Human Brain.
  4. ↑ Klowden MJ (July 2003). "Contributions of insect research toward our understanding of neurosecretion". Archives of Insect Biochemistry and Physiology. 53 (3): 101–114. doi:10.1002/arch.10093. PMID   12811763.
  5. 1 2 Forbes AP (1963). "Neurosecretions; proceedings of the third International Symposium on Neurosecretion, held in the University of Bristol, September, 1961. Memoirs of the Society for Endocrinology No 12". JAMA: The Journal of the American Medical Association. 184: 82. doi:10.1001/jama.1963.03700140138036.
  6. ↑ Meyer J. "Insect Physiology: The Endocrine System". General Entomology NC State University.
  7. ↑ "Oxford Dictionary". Instar: Definition of Instar in Oxford Dictionary (American English.
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