wiki笔记--Paraventricular nucleus of hypothalamus--2021/8/20

Paraventricular nucleus of hypothalamus

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Not to be confused with Periventricular nucleus.

Paraventricular nucleus of hypothalamus

 

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).

 

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]

 

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，这一效果基本上是所有科学家都没有想到过的，因为vasopressin对小动脉的管径有很明显作用，即增强血流阻力，在交感系统还不十分活跃的情况下通过vasopressin来调整血流分布。这个调节是即时性的，是神经细胞直接释放到血液中立马见成效的吗，是可以一定程度自我控制的。

往往甲状腺激素与cortisol激素同时增加，而二者都是提高交感系统的活动。显然日常的一般状态下的交感系统就应该是由这二者来激发，而紧急状态下的交感系统激发是通过NE放大系统快速激发，还包括那些能激发肾上腺的神经元。

练硬气功的人应该是促进parvocellular neurosecretory neurons来加强cortisol和vasopressin的释放，从而调整血流的分布和血压，这样的人不能思考，只能死扛，因为一旦动用海马皮层思考，他们就减少了cortisol的含量。他们应该只动用dorsal visual stream而不动用temporal cortex的ventral visual stream which will involve 海马皮层，这样的话他们劈砖的时候是通过anterior cingulate cortex去感受疼痛，甚至通过median raphe nucleus来加强anterior cingulate cortex的serotonin浓度而降低limbic cortex的敏感度（这样也减少了海马皮层的输出），从而降低疼痛信息对anterior cingulate cortex的作用，同时形成anterior cingulate cortex-prefrontal cortex-parietal cortex的记忆结构。一旦用海马皮层去思考劈砖带来的疼痛就会降低cortisol的浓度，从而影响血压和血液的分布，就比如硬邦邦的车胎是结实的不怕硬，而软一些的车胎很容易被硬的东西硌坏内部(是车胎内部相互揉搓导致坏掉)，同样道理，局部血压高的手皮肤和骨头因高血压而变硬，用这样的手去劈砖时不容易造成内伤。 ）

由上面两个图得出一些想法：

在笼子里的动物坐等食物自来投，野生动物主动搜寻食物；动物幼崽坐等食物自来投，不能主动搜寻食物，此时动物幼崽的NE放大系统还不成熟。或许平常状态下人体是在DA system状态下运行，使用cortisol和甲状腺素作为主要兴奋交感系统的方式，而在饥饿诱发的欲望状态下，cortisol和甲状腺素被抑制，NE放大系统走到DA system前面进行运行，肾上腺素成了主要的交感系统兴奋源。但是，海马皮层的活动会抑制cortisol的释放。而海马皮层的活动意味着cingulate cortex也活动，同时通过anterior cingulate cortex投射到anterior insular cortex，带动insular cortex也活动。