Paraventricular nucleus of hypothalamus

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Not to be confused with?Periventricular nucleus.

Paraventricular nucleus of hypothalamus

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Human paraventricular nucleus (PVN) in this coronal section is indicated by the shaded area. Dots represent?vasopressin(AVP) neurons (also seen in the?supraoptic nucleus, SON). The medial surface is the 3rd ventricle (3V).

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The paraventricular hypothalamus of the mouse brain

Details

Identifiers

Latin

Nucleus paraventricularis hypothalami

MeSH

D010286

NeuroNames

387

NeuroLex?ID

birnlex_1407

TA98

A14.1.08.909

TA2

5722

FMA

62320

Anatomical terms of neuroanatomy

[edit on Wikidata]

The?paraventricular nucleus?(PVN,?PVA, or?PVH) 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).[1]?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.[2]

Contents

·?1Location

·?2Neurons

·?2.1Magnocellular neurosecretory neurons

·?2.2Parvocellular neurosecretory neurons

·?2.3Centrally-projecting neurons

·?3Afferent inputs

·?4References

·?5Further reading

Location[edit]

The paraventricular nucleus lies adjacent to the?third ventricle. It lies within the periventricular zone and is not to be confused with the?periventricular nucleus, which occupies a more medial position, beneath the?third ventricle. The PVN is highly vascularised?and is protected by the?blood–brain barrier, although its?neuroendocrine cells?extend to sites (in the?median eminence?and in the?posterior pituitary) beyond the blood–brain barrier.

Neurons[edit]

The PVN contains?magnocellular neurosecretory cells?whose?axons?extend into the?posterior pituitary,?parvocellular neurosecretory cells?that project to the?median eminence, ultimately signalling to the?anterior pituitary, and several populations of other cells that project to many different brain regions including parvocellular preautonomic cells that project to the?brainstem?and?spinal cord.

Magnocellular neurosecretory neurons[edit]

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Magnocellular neurons of the PVN and SON project to the?posterior pituitary

The?magnocellular?cells in the PVN elaborate and secrete two?peptide hormones:?oxytocin?and?vasopressin.

These hormones are packaged into large vesicles, which are then transported down the?unmyelinated?axons?of the cells and released from neurosecretory nerve terminals residing in the posterior pituitary gland.

Similar magnocellular neurons are found in the?supraoptic nucleus?which also secrete vasopressin and a smaller amount of oxytocin.

Parvocellular neurosecretory neurons[edit]

The axons of the?parvocellular?neurosecretory neurons of the PVN project to the median eminence, a neurohemal organ at the base of the brain, where their neurosecretory nerve terminals release their hormones at the primary capillary plexus of the?hypophyseal portal system. The median eminence contains fiber terminals from many hypothalamic neuroendocrine neurons, secreting different neurotransmitters or neuropeptides, including vasopressin, corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH), gonadotropin-releasing hormone (GnRH), growth hormone-releasing hormone (GHRH), dopamine (DA) and somatostatin (growth hormone release inhibiting hormone, GIH) into blood vessels in the hypophyseal portal system. The blood vessels carry the peptides to the anterior pituitary gland, where they regulate the secretion of hormones into the systemic circulation. The parvocellular neurosecretory cells include those that make:

·?Corticotropin-releasing hormone?(CRH), which regulates?ACTH?secretion from the?anterior pituitary gland

·?Vasopressin, which also regulates ACTH secretion (vasopressin and CRH act synergistically to stimulate ACTH secretion)

·?Thyrotropin-releasing hormone?(TRH), which regulates?TSH?and?prolactin?secretion

Centrally-projecting neurons[edit]

As well as neuroendocrine neurons, the PVN contains?interneurons?and populations of neurons that project centrally (i.e., to other brain regions). The centrally-projecting neurons include

·?Parvocellular oxytocin cells, which project mainly to the?brainstem?and?spinal cord. These neurons are thought to have a role in gastric reflexes and penile erection,[3][4]

·?Parvocellular vasopressin cells, which project to many points in the hypothalamus and?limbic system, as well as to the brainstem and spinal cord (these are involved in blood pressure and temperature regulation), and?brown fat?thermogenesis.

·?Parvocellular CRH neurons, which are thought to be involved in stress-related behaviors.

Afferent inputs[edit]

The PVN receives afferent inputs from many brain regions and different parts of the body, by hormonal control.[2]

Among these, inputs from neurons in structures adjacent to the anterior wall of the third ventricle (the "AV3V region") carry information about the electrolyte composition of the blood, and about circulating concentrations of such hormones as?angiotensin?and?relaxin, to regulate the magnocellular neurons.[5]

Inputs from the brainstem (the?nucleus of the solitary tract) and the ventrolateral medulla carry information from the heart and?stomach. Inputs from the?hippocampus?to the CRH neurones are important regulators of stress responses.

Inputs from?neuropeptide Y-containing neurons in the?arcuate nucleus?coordinate metabolic regulation (via TRH secretion) with regulation of energy intake.[6][7][8]?Specifically, the projections from the arcuate nucleus seem to exert their effect on appetite via?MC4R-expressing oxytocinergic cells of the PVN.[9]

Inputs from?suprachiasmatic nucleus?about levels of lighting (circadian rhythms).

Inputs from glucose sensors within the brain stimulate release of?vasopressin?and?corticotropin-releasing hormone?from?parvocellular neurosecretory cells.

（vasopressin的重要作用是distribution of blood flow，血流分布，這一效果基本上是所有科學(xué)家都沒有想到過的，因為vasopressin對小動脈的管徑有很明顯作用，即增強血流阻力，在交感系統(tǒng)還不十分活躍的情況下通過vasopressin來調(diào)整血流分布。這個調(diào)節(jié)是即時性的，是神經(jīng)細胞直接釋放到血液中立馬見成效的嗎，是可以一定程度自我控制的。

往往甲狀腺激素與cortisol激素同時增加，而二者都是提高交感系統(tǒng)的活動。顯然日常的一般狀態(tài)下的交感系統(tǒng)就應(yīng)該是由這二者來激發(fā)，而緊急狀態(tài)下的交感系統(tǒng)激發(fā)是通過NE放大系統(tǒng)快速激發(fā)，還包括那些能激發(fā)腎上腺的神經(jīng)元。

練硬氣功的人應(yīng)該是促進parvocellular neurosecretory neurons來加強cortisol和vasopressin的釋放，從而調(diào)整血流的分布和血壓，這樣的人不能思考，只能死扛，因為一旦動用海馬皮層思考，他們就減少了cortisol的含量。他們應(yīng)該只動用dorsal visual stream而不動用temporal cortex的ventral visual stream which will involve 海馬皮層，這樣的話他們劈磚的時候是通過anterior cingulate cortex去感受疼痛，甚至通過median raphe nucleus來加強anterior cingulate cortex的serotonin濃度而降低limbic cortex的敏感度（這樣也減少了海馬皮層的輸出），從而降低疼痛信息對anterior cingulate cortex的作用，同時形成anterior cingulate cortex-prefrontal cortex-parietal cortex的記憶結(jié)構(gòu)。一旦用海馬皮層去思考劈磚帶來的疼痛就會降低cortisol的濃度，從而影響血壓和血液的分布，就比如硬邦邦的車胎是結(jié)實的不怕硬，而軟一些的車胎很容易被硬的東西硌壞內(nèi)部(是車胎內(nèi)部相互揉搓導(dǎo)致壞掉)，同樣道理，局部血壓高的手皮膚和骨頭因高血壓而變硬，用這樣的手去劈磚時不容易造成內(nèi)傷。?）

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由上面兩個圖得出一些想法：

在籠子里的動物坐等食物自來投，野生動物主動搜尋食物；動物幼崽坐等食物自來投，不能主動搜尋食物，此時動物幼崽的NE放大系統(tǒng)還不成熟?；蛟S平常狀態(tài)下人體是在DA system狀態(tài)下運行，使用cortisol和甲狀腺素作為主要興奮交感系統(tǒng)的方式，而在饑餓誘發(fā)的欲望狀態(tài)下，cortisol和甲狀腺素被抑制，NE放大系統(tǒng)走到DA system前面進行運行，腎上腺素成了主要的交感系統(tǒng)興奮源。但是，海馬皮層的活動會抑制cortisol的釋放。而海馬皮層的活動意味著cingulate cortex也活動，同時通過anterior cingulate?cortex投射到anterior insular cortex，帶動insular cortex也活動。

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