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27-453: The anteroventral periventricular nucleus ( AVPV ) is a small cluster of cells located in the preoptic area of hypothalamus of the brain that is abundant in nuclear hormone receptors in a sexually dimorphic manner, strongly implicated, in rat models, as being neonatally imprinted and subsequently controlling sex-typical physiology and behaviors. This nucleus or cluster of cells is typically of bigger size in females than males, contrary to

54-438: A starch indicator . Iodine is reduced by ascorbic acid, and when all the ascorbic acid has reacted, the iodine is in excess, forming a blue-black complex with the starch indicator. This indicates the end-point of the titration. As an alternative, ascorbic acid can be treated with iodine in excess, followed by back titration with sodium thiosulfate using starch as an indicator. This iodometric method has been revised to exploit

81-550: A potentially dangerous pro-oxidative compound in certain metabolic contexts. Ascorbic acid and its sodium, potassium, and calcium salts are commonly used as antioxidant food additives . These compounds are water-soluble and, thus, cannot protect fats from oxidation: For this purpose, the fat- soluble esters of ascorbic acid with long-chain fatty acids (ascorbyl palmitate or ascorbyl stearate) can be used as antioxidant food additives. It creates volatile compounds when mixed with glucose and amino acids at 90 °C. It

108-423: A proton results in a 1,3-diketone: The ascorbate ion is the predominant species at typical biological pH values. It is a mild reducing agent and antioxidant . It is oxidized with loss of one electron to form a radical cation and then with loss of a second electron to form dehydroascorbic acid . It typically reacts with oxidants of the reactive oxygen species , such as the hydroxyl radical . Ascorbic acid

135-687: Is a cofactor in tyrosine oxidation . The main use of l -ascorbic acid and its salts is as food additives, mostly to combat oxidation. It is approved for this purpose in the EU with E number E300, the US, Australia, and New Zealand. Another major use of l -ascorbic acid is as a dietary supplement . It is on the World Health Organization's List of Essential Medicines . Natural biosynthesis of vitamin C occurs through various processes in many plants and animals. Seventy percent of

162-403: Is responsible for thermoregulation and receives nervous stimulation from thermoreceptors in the skin, mucous membranes , and hypothalamus itself. The median preoptic nucleus is located along the midline in a position significantly dorsal to the other three preoptic nuclei, at least in the crab-eating macaque brain. It wraps around the top (dorsal), front, and bottom (ventral) surfaces of

189-426: Is special because it can transfer a single electron, owing to the resonance-stabilized nature of its own radical ion , called semidehydroascorbate . The net reaction is: On exposure to oxygen , ascorbic acid will undergo further oxidative decomposition to various products including diketogulonic acid , xylonic acid , threonic acid and oxalic acid . Reactive oxygen species are damaging to animals and plants at

216-523: Is the one most often encountered: it occurs naturally in many foods, and is one form (" vitamer ") of vitamin C , an essential nutrient for humans and many animals. Deficiency of vitamin C causes scurvy , formerly a major disease of sailors in long sea voyages. It is used as a food additive and a dietary supplement for its antioxidant properties. The " d " form can be made via chemical synthesis , but has no significant biological role. The antiscorbutic properties of certain foods were demonstrated in

243-458: Is used in the predominant process used by the ascorbic acid industry in China, which supplies 70% of the world's ascorbic acid. Researchers are exploring means for one-step fermentation. The traditional way to analyze the ascorbic acid content is by titration with an oxidizing agent , and several procedures have been developed. The popular iodometry approach uses iodine in the presence of

270-620: The anterior commissure . The median preoptic nucleus generates thirst . Drinking decreases noradrenaline release in the median preoptic nucleus. The medial preoptic nucleus is bounded laterally by the lateral preoptic nucleus, and medially by the preoptic periventricular nucleus. It releases gonadotropin-releasing hormone (GnRH), controls copulation in males, and is larger in males than in females. The medial preoptic area (mPOA) has been implicated in parental care in both males and females. In rats, oxytocin and vasopressin are associated with maintaining maternal care through local release in

297-587: The sexually dimorphic nucleus (SDN) that is bigger in males. In rats and mice, the AVPV plus the periventricular nucleus make up the rostral periventricular region of the third ventricle (RP3V). This area is full of kisspeptin -expressing neurons and is involved in regulating GnRH neurons, and is responsible for the LH surge in female mice. This neuroanatomy article is a stub . You can help Misplaced Pages by expanding it . Preoptic area The preoptic area

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324-433: The 18th century by James Lind . In 1907, Axel Holst and Theodor Frølich discovered that the antiscorbutic factor was a water-soluble chemical substance, distinct from the one that prevented beriberi . Between 1928 and 1932, Albert Szent-Györgyi isolated a candidate for this substance, which he called it "hexuronic acid", first from plants and later from animal adrenal glands. In 1932 Charles Glen King confirmed that it

351-632: The acidity of one of the enol hydroxyl groups . The deprotonated conjugate base is the ascorbate anion, which is stabilized by electron delocalization that results from resonance between two forms: For this reason, ascorbic acid is much more acidic than would be expected if the compound contained only isolated hydroxyl groups. The ascorbate anion forms salts , such as sodium ascorbate , calcium ascorbate , and potassium ascorbate . Ascorbic acid can also react with organic acids as an alcohol forming esters such as ascorbyl palmitate and ascorbyl stearate . Nucleophilic attack of ascorbic acid on

378-607: The bleaching solution. Acid-catalyzed hydrolysis of this product performs the dual function of removing the two acetal groups and ring-closing lactonization . This step yields ascorbic acid. Each of the five steps has a yield larger than 90%. A biotechnological process, first developed in China in the 1960s but further developed in the 1990s, bypassing acetone-protecting groups. A second genetically modified microbe species, such as mutant Erwinia , among others, oxidises sorbose into 2-ketogluconic acid (2-KGA), which can then undergo ring-closing lactonization via dehydration. This method

405-552: The compound, and later specifically l -ascorbic acid. Because of their work, in 1937 two Nobel Prizes : in Chemistry and in Physiology or Medicine were awarded to Haworth and Szent-Györgyi, respectively. Ascorbic acid is a furan -based lactone of 2-ketogluconic acid . It contains an adjacent enediol adjacent to the carbonyl . This −C(OH)=C(OH)−C(=O)− structural pattern is characteristic of reductones , and increases

432-410: The immediate early gene c-fos , in experienced rat mothers or fathers when compared to controls. Also in fathers, studies have shown that when they receive ultrasonic or pheromone cues from their mates, their c-fos expression in the mPOA further increased, suggestive that rat paternal behavior is mediated through the mPOA but activated by direct interactions with a mate. Large lesions of the mPOA disrupt

459-400: The latency to ejaculate. Furthermore, testosterone implanted into the mPOA of castrated males completely restores mating, as long as aromatase is not inhibited. The ventrolateral preoptic nucleus , or intermediate nucleus, is adjacent to the medial preoptic nucleus. It also mediates non-REM sleep onset. The preoptic periventricular nucleus is located along the midline and is medial to

486-557: The mPOA and the adjacent bed nucleus of the stria terminalis (BNST). Oxytocin and vasopressin V1a receptor binding are increased in both the mPOA and the BNST in lactating rats when compared to controls. The mPOA also has a high density of estradiol receptors that, when activated, can cause a male rat to show maternal-type behaviors. Additionally, the mPOA is critical for the onset and expression of parental behavior, as evidenced by increases in

513-550: The mPOA. Since ascorbic acid (Vitamin C) enhances DA transmission in mesolimbic and nigrostriatal pathways, it has been shown that infusions of ascorbic acid into the mPOA increases appetitive behaviors compared to controls. In male rats, the mPOA affects the consummatory phase of sexual behavior, and possibly motivation, with lesions causing a complete loss of copulatory behaviors. Conversely, electrical stimulation of this area triggers male copulatory behavior, as measured by decreases in

540-501: The medial amygdala (MA) and BNST. Studies using female Syrian hamsters have shown that the mPOA is important for sexual odor preference. While control females will investigate male odors more than female odors, those with bilateral lesions to the mPOA (MPOA-X) will show no difference in odor preference, but vaginal scent marking and lordosis remained unaffected. Appetitive behaviors of female rats – including hops, darts, and solicitations – have been linked to dopamine (DA) transmission in

567-490: The medial preoptic nucleus. Ascorbic acid Ascorbic acid is an organic compound with formula C 6 H 8 O 6 , originally called hexuronic acid . It is a white solid, but impure samples can appear yellowish. It dissolves freely in water to give mildly acidic solutions. It is a mild reducing agent . Ascorbic acid exists as two enantiomers (mirror-image isomers ), commonly denoted " l " (for "levo") and " d " (for "dextro"). The l isomer

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594-489: The molecular level due to their possible interaction with nucleic acids , proteins, and lipids. Sometimes these radicals initiate chain reactions. Ascorbate can terminate these chain radical reactions by electron transfer . The oxidized forms of ascorbate are relatively unreactive and do not cause cellular damage. However, being a good electron donor, excess ascorbate in the presence of free metal ions can not only promote but also initiate free radical reactions, thus making it

621-401: The onset of maternal behavior, nest-building, and pup retrieval, with the lateral projections being especially critical. The mPOA is sexually dimorphic, that is, it differs in function between males and females. In females, studies have examined the influence of the mPOA on precopulatory and appetitive behaviors. Precopulatory behaviors involve several brain areas, including the mPOA as well as

648-475: The product with acetone in the presence of an acid catalyst converts four of the remaining hydroxyl groups to acetals . The unprotected hydroxyl group is oxidized to the carboxylic acid by reaction with the catalytic oxidant TEMPO (regenerated by sodium hypochlorite  – bleaching solution). Historically, industrial preparation via the Reichstein process used potassium permanganate as

675-416: The reaction of ascorbic acid with iodate and iodide in acid solution. Electrolyzing the potassium iodide solution produces iodine, which reacts with ascorbic acid. The end of the process is determined by potentiometric titration like Karl Fischer titration . The amount of ascorbic acid can be calculated by Faraday's law . Another alternative uses N -bromosuccinimide (NBS) as the oxidizing agent in

702-481: The world's supply of ascorbic acid is produced in China. Ascorbic acid is prepared in industry from glucose in a method based on the historical Reichstein process . In the first of a five-step process, glucose is catalytically hydrogenated to sorbitol , which is then oxidized by the microorganism Acetobacter suboxydans to sorbose . Only one of the six hydroxy groups is oxidized by this enzymatic reaction. From this point, two routes are available. Treatment of

729-454: Was indeed the antiscorbutic factor. In 1933, sugar chemist Walter Norman Haworth , working with samples of "hexuronic acid" that Szent-Györgyi had isolated from paprika and sent him in the previous year, deduced the correct structure and optical-isomeric nature of the compound, and in 1934 reported its first synthesis. In reference to the compound's antiscorbutic properties, Haworth and Szent-Györgyi proposed to rename it "a-scorbic acid" for

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