Abstract: Nitric oxide (NO) is one of the most simple and versatile biosignal molecules in organisms with unique physicochemical properties and biological activities. NO can regulate the female reproductive process, such as ovulation, implantation, maintenance of pregnancy, regulation of childbirth, regulation of the estrus cycle. Recent studies have shown that NO also plays an important neuromodulatory role in female sexual maturation. This article reviews the neuromodulation of female sexual maturation by N0.
Nitric oxide (NO) is one of the most simple and versatile biosignal molecules in living organisms. It also plays a biological signal molecule with multiple physiological functions such as second messenger, neurotransmitter and effector molecule. Physiological effects. Studies have confirmed that NO can regulate the female reproductive process, such as ovulation, implantation, maintenance of pregnancy, regulation of childbirth, regulation of the estrus cycle. Recent studies have shown that NO also plays an important role in neuroregulation during female sexual maturation.
In vivo, NO is synthesized by L-arginine catalyzed by nitric oxide synthase (NOS) and can be almost completely converted to nitrate. NOS can be divided into three types, namely, neural tissue type NO synthase (nNOS), endothelial tissue type NO synthase (eNOS), and inducible NO synthase (iNOS). As a key factor in the production of NO, NOS is widely distributed in a variety of tissues and plays a very important role in the physiological role of NO.
1. Expression of NO-related genes in the reproductive axis system Starts Here.
nNOS is widely expressed in female mice and rat hypothalamus. nNOS and eNOS coexist in the median bulge of female rats; eNOS expression was found in the anterior pituitary of rats, and NOS neurons were also found in gonadoblasts. NOS is also widely expressed in porcine follicles. nNOS and eNOS are present in ovarian surface epithelium, interstitial, oocyte, membrane cells and vascular epithelial cells. nNOS and iNOS are present in granulosa cells of multiple layers and vesicular follicles in large follicles. . In large follicles, eNOS than granule cells expressed in oocytes to be more
2. NO regulates hormones and neuromodulators.
In addition to the widespread expression of NOS in the hypothalamic-pituitary-gonadal axis, studies have found that NO plays a role in some hormones and neuromodulators in the reproductive axis, and these substances are involved in reproduction (Table 1). This further indicates that NO may regulate the sexual development and reproductive activities of females through the hypothalamic-pituitary-gonadal axis.
3. NO-GnRH and sexual development
3.1 ERα, NOS, GnRH co-expression of
NOS neurons exist in GnRH-regulated sites in many areas of the hypothalamus, such as endplate microvessels, anterior medial anterior medial nucleus, ventromedial nucleus, arcuate nucleus, and median ridge. NOS and estrogen receptor alpha (ERα) double-stained neurons are widely distributed in the hypothalamus. The action of estrogen in the hypothalamus is achieved by NO-mediated, that is, NO is the second messenger produced by estrogen acting on its receptor. Complete physiological functions.
3.2 ERα-NOS-NO-GnRH and sexual development
NO is thought to regulate reproductive activity through the effects of hypothalamic and pituitary levels. The mechanism may be that NO promotes the secretion of GnRH, and then promotes the secretion of FSH and PRL in the pituitary gland, and also stimulates estrus. Lamar et al. found that the expression of nNOS in the preoptic area of ​​the hypothalamus was accompanied by the release of the GnRH/LH peak. In vivo studies have also confirmed that blocking the release of NO in ME results in a cessation of the female estrus cycle. Intracerebral injection of eNOS antisense oligonucleotides in the gonadectomy rats inhibited steroid-induced GnRH/LH peaks, confirming that eNOS plays an important regulatory role in GnRH secretion.
NO is a natural regulator of GnRH neuronal excitability, and NOS neurons transmit stimulation and inhibition information into GnRH neurons. In the early stage of estrus, the proportion of nNOS neurons producing NO was significantly higher than other periods, and NO may be a transient switch of GnRH pulse release and peak appearance before estrus. All of this is related to the dynamic activity of estrogen. In the preoptic area, all nNOS neurons express ERα, and nNOS neurons are likely to be directly involved in the positive feedback of estrogen in the brain. At the same time, the enzyme activity of nNOS is strictly regulated by estrogen, and The estrus reached its maximum in the early stage. The undulating estrogen levels during the estrous cycle regulate the activity of nNOS by altering the phosphorylation level of nNOS in the pre-opportunal region.
The median uplift is considered to be a key site regulating GnRH release. The NO produced by the expression of eNOS neurons is pulsed and periodically released, exhibiting the same pulse frequency as GnRH, and treatment with inhibitors of eNOS can simultaneously inhibit the release of NO and GnRH. The release of NO/GnRH in the median uplift is strongly regulated by estrogen in a manner that regulates eNOS activity through an ER-dependent pathway that promotes changes in intracellular calcium concentration in epithelial cells. In summary, during sexual development, the neuroendocrine system of the brain utilizes NO to coordinate GnRH neuronal activity and GnRH release.
3.3 Some molecules coordinate the regulation of NO and GnRH
There is also another evidence that NO regulates reproduction through GnRH, that is, some molecules have the same position and effect on the regulation of NO and GnRH (Table 2), which further demonstrates that both NO and GnRH play a biological role in vivo. There is a very close relationship when learning.
4. NO-Kisspeptins and sexual development
KISS-1 (the gene encoding kisspeptin) and its receptor GPR54 (G protein-coupled receptor 54) genes play an important role in the normal initiation of puberty. Kisspeptin/GPR54 is a key regulator and catalyst for priming initiation and is a gatekeeper gene that controls mammalian sexual maturation.
NO may play an important role in the kisspeptin signal as an intermediate synchronous "switch". In the preoptic area of ​​the hypothalamus, there is a morphological interaction between kisspeptin and nNOS neurons, and nNOS neurons express the kisspeptin receptor. Recent studies have shown that kisspeptin neurons act directly on GnRH neuronal elements or through synaptic transmission. Therefore, the interaction of nNOS with kisspeptin plays an important role in the regulation of the hypothalamic-pituitary-gonadal axis. In addition to the acts of kisspeptin neurons acting directly on GnRH neurons or through synaptic transmission, the kisspeptin nerves will also "tell" nNOS neurons and stimulate NO production, which may be an intermediate synchronous "switch" that stimulates GnRH release. At the same time, in the midst of the uplift, kisspeptin is positively feedback by estrogen to regulate the pulse secretion of GnRH/LH.
Existing studies have shown that NO plays an important regulatory role in female sexual maturation in the pre-optic and median bulges. In the preoptic area, NO neurons may control the abrupt activation of GnRH neuronal activity, whereas in the median bulge, NO produced by endothelial cells may represent a synchronous signal that coordinates the release of GnRH at the neuroendocrine end, thus forming a unique regulatory mechanism. That is, GnRH is accurately transported into the pituitary during sexual activity. At the same time, the activity of NO synthase is strictly regulated by estrogen, forming a regulatory developmental and sexually mature Era-NOS-(kisspeptin)-GnRH neural pathway.
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