Neuroendocrinology

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Neuroendocrinology is the branch of

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.

The

.

Neuroendocrine system

Hypothalamus

Hypothalamic interaction with the posterior and anterior pituitary glands. The hypothalamus produces the hormones oxytocin and vasopressin in its endocrine cells (left). These are released at nerve endings in the posterior pituitary gland and then secreted into the systemic circulation. The hypothalamus releases tropic hormones into the hypophyseal portal system to the anterior pituitary (right). The anterior pituitary then secretes trophic hormones into the circulation which elicit different responses from various target tissues. These responses then signal back to the hypothalamus and anterior pituitary to either stop producing or continue to produce their precursor signals.

The hypothalamus is commonly known as the relay center of the brain because of its role in integrating inputs from all areas of the brain and producing a specific response. In the neuroendocrine system, the hypothalamus receives electrical signals from different parts of the brain and translates those electrical signals into chemical signals in the form of hormones or releasing factors. These chemicals are then transported to the pituitary gland and from there to the systemic circulation.[2]

Pituitary gland

The pituitary gland is divided into three lobes: the anterior pituitary, the intermediate pituitary lobe, and the posterior pituitary. The hypothalamus controls the anterior pituitary's hormone secretion by sending releasing factors, called tropic hormones, down the hypothalamo-hypophysial portal system.[3] For example, thyrotropin-releasing hormone released by the hypothalamus in to the portal system stimulates the secretion of thyroid-stimulating hormone by the anterior pituitary.[citation needed]

The posterior pituitary is directly innervated by the hypothalamus; the hormones

systemic circulation by the hypothalamic neurons.[3]

Major neuroendocrine axes

paraventricular nucleus and supraoptic nucleus of the hypothalamus, respectively,[2] and the electrical activity of these neurons is regulated by afferent synaptic inputs from other brain regions.[4]

By contrast, the hormones of the

adrenocorticotrophic hormone, luteinizing hormone, follicle-stimulating hormone, thyroid-stimulating hormone, prolactin, and growth hormone) remains under the control of the hypothalamus. The hypothalamus controls the anterior pituitary gland via releasing factors and release-inhibiting factors; these are substances released by hypothalamic neurons into blood vessels at the base of the brain, at the median eminence.[5] These vessels, the hypothalamo-hypophysial portal vessels, carry the hypothalamic factors to the anterior pituitary, where they bind to specific receptors on the surface of the hormone-producing cells.[3]

For example, the secretion of growth hormone is controlled by two neuroendocrine systems: the

peptides into portal blood vessels for transport to the anterior pituitary. Growth hormone is secreted in pulses, which arise from alternating episodes of GHRH release and somatostatin release, which may reflect neuronal interactions between the GHRH and somatostatin cells, and negative feedback from growth hormone.[6]

Functions

The neuroendocrine systems control reproduction

parturition, lactation, and maternal behaviour. They control the body's response to stress[8] and infection.[9] They regulate the body's metabolism, influencing eating and drinking behaviour, and influence how energy intake is utilised, that is, how fat is metabolised.[10] They influence and regulate mood,[11] body fluid and electrolyte homeostasis,[12] and blood pressure.[13]

The neurons of the neuroendocrine system are large; they are mini factories for producing secretory products; their nerve terminals are large and organised in coherent terminal fields; their output can often be measured easily in the blood; and what these neurons do and what stimuli they respond to are readily open to hypothesis and experiment. Hence, neuroendocrine neurons are good "model systems" for studying general questions, like "how does a neuron regulate the synthesis, packaging, and secretion of its product?" and "how is information encoded in electrical activity?"[citation needed][It appears that this is a primary source observation.]

History

Pioneers

Walter Lee Gaines noted the activity of the pituitary in the lactation of cows in 1915.[14] He also noted that anaesthesia could block lactation and response to the suckling reflex.[15]

Ernst and

University of Munich the Albert Einstein College of Medicine are credited as co-founders the field of neuroendocrinology with their initial observations and proposals in 1945 concerning neuropeptides
.

systemic circulation directly from the nerve endings of hypothalamic neurons. This seminal work was done in collaboration with Dora Jacobsohn of Lund University.[18]

The first of these factors to be identified are thyrotropin-releasing hormone (TRH) and gonadotropin-releasing hormone (GnRH). TRH is a small peptide that stimulates the secretion of thyroid-stimulating hormone; GnRH (also called luteinizing hormone-releasing hormone) stimulates the secretion of luteinizing hormone and follicle-stimulating hormone.

Andrew W. Schally of Tulane University isolated these factors from the hypothalamus of sheep and pigs, and then identified their structures. Guillemin and Schally were awarded the Nobel Prize in Physiology and Medicine in 1977 for their contributions to understanding "the peptide hormone production of the brain".[citation needed
]

In 1952,

Andor Szentivanyi, of the University of South Florida, and Geza Filipp wrote the world's first research paper showing how neural control of immunity takes place through the hypothalamus.[20]

Modern scope

Today, neuroendocrinology embraces a wide range of topics that arose directly or indirectly from the core concept of neuroendocrine neurons. Neuroendocrine neurons control the

noradrenaline proved to have properties between endocrine cells and neurons, and proved to be outstanding model systems for instance for the study of the molecular mechanisms of exocytosis
. And these, too, have become, by extension, neuroendocrine systems.

Neuroendocrine systems have been important to our understanding of many basic principles in neuroscience and physiology, for instance, our understanding of stimulus-secretion coupling.[21] The origins and significance of patterning in neuroendocrine secretion are still dominant themes in neuroendocrinology today.

Neuroendocrinology is also used as an integral part of understanding and treating

neurobiological brain disorders. One example is the augmentation of the treatment of mood symptoms with thyroid hormone.[22] Another is the finding of a transthyretin (thyroxine transport) problem in the cerebrospinal fluid of some patients diagnosed with schizophrenia.[23]

Experimental techniques

Since the original experiments by Geoffrey Harris investigating the communication of the hypothalamus with the pituitary gland, much has been learned about the mechanistic details of this interaction. Various experimental techniques have been employed. Early experiments relied heavily on the electrophysiology techniques used by Hodgkin and Huxley. Recent approaches have incorporated various mathematical models to understand previously identified mechanisms and predict systemic response and adaptation under various circumstances.[citation needed]

Electrophysiology

Electrophysiology experiments were used in the early days of neuroendocrinology to identify the physiological happenings in the hypothalamus and the posterior pituitary especially. In 1950, Geoffrey Harris and Barry Cross outlined the oxytocin pathway by studying oxytocin release in response to electrical stimulation.[24] In 1974, Walters and Hatton investigated the effect of water dehydration by electrically stimulating the supraoptic nucleus—the hypothalamic center responsible for the release of vasopressin.[24] Glenn Hatton dedicated his career to studying the physiology of the Neurohypophyseal system, which involved studying the electrical properties of hypothalamic neurons.[24] Doing so enabled investigation into the behavior of these neurons and the resulting physiological effects. Studying the electrical activity of neuroendocrine cells enabled the eventual distinction between central nervous neurons, neuroendocrine neurons, and endocrine cells.[25]

Mathematical Models

Hodgkin-Huxley Model

The Hodgkin–Huxley model translates data about the current of a system at a specific voltage into time-dependent data describing the membrane potential. Experiments using this model typically rely on the same format and assumptions, but vary the differential equations to answer their particular questions. Much has been learned about vasopressin, GnRH, somatotrophs, corticotrophs, and lactotrophic hormones by employing this method.[8]

Integrate-and-Fire Model

The integrate-and-fire model aims for mathematic simplicity in describing biological systems by focusing on, and only on the threshold activity of a neuron. By doing so, the model successfully reduces the complexity of a complicated system; however it ignores the actual mechanisms of action and replaces them with functions that define how the output of a system depends on its input.[8] This model has been used to describe the release of hormones to the posterior pituitary gland, specifically oxytocin and vasopressin.[9]

Functional or Mean Fields Model

The functional or mean fields model relies on the premise "simpler is better".[8] It strives to reduce the complexity of modelling multi-faceted systems by using a single variable to describe an entire population of cells. The alternative would be to use a different set of variables for each population. When attempting to model a system where multiple populations of cells interact, using several sets quickly becomes overcomplicated. This model has been used to describe several systems, especially involving the reproductive cycle (menstrual cycles, luteinizing hormone, prolactin surges).[9] Functional models also exist to represent cortisol secretion, and growth hormone secretion.[9]

See also

References

  1. ^ "Endocrine system and neuroendocrinology :: DNA Learning Center". www.dnalc.org. Retrieved 2018-05-12.
  2. ^
    PMID 25994006
    .
  3. ^ .
  4. .
  5. , retrieved 2021-11-15
  6. ^ .
  7. .
  8. ^ .
  9. ^
    PMID 11861600. Archived from the original
    (PDF) on 2013-12-12.
  10. .
  11. .
  12. .
  13. .
  14. ^ Medvei, V.C. (2012). A History of Endocrinology. Springer. p. 409.
  15. .
  16. .
  17. PMID 9056724. Archived from the original
    (PDF) on 2007-07-03. Retrieved 2006-02-10.
  18. S2CID 8177884. Archived from the original
    (PDF) on 2018-12-24.
  19. .
  20. ^ Berczi I (2010). "Dr Andor Szentivanyi Memorial". University of Manitoba. Archived from the original on 2009-02-10. (Warning: automatic background music)
  21. PMID 19745043
    .
  22. ^ Geracioti TD (2006). "Identifying Hypothyroidism's Psychiatric Presentations". Current Psychiatry. 5 (11): 98–117.
  23. PMID 17090210
    .
  24. ^ .
  25. .