Book 2 Listening (1108796), страница 19
Текст из файла (страница 19)
But sometimes even these good habits are insufficient to shift such films,and a chemical called chlorhexidine has to be deployed as well, in the form of a mouthwash.Chlorhexidine, however, stains teeth and affects people’s sense of taste, so an alternativewould be welcome.
And Victoria Moreno-Arribas of the Institute of Food Science Research inMadrid believes she may have one: a derivative of red wine.Dr Moreno-Arribas knew from previous work that red wine has antimicrobial properties,but she could find few studies which looked at whether it attacks dental biofilms specifically.To rectify that, she and her colleagues grew five troublesome oral bacteria, Actinomyces oris,Fusobacterium nucleatum, Streptococcus mutans, Streptococcus oralis and Veillonelladispar, on discs of hydroxyapatite, the main component of dental enamel. They fed the bugsby dipping the discs into solutions of sugar mixed with saliva collected from volunteers, whospent several hours spitting into jars.
The results have just been published in the Journal ofAgricultural and Food Chemistry.As expected, the bacteria grew to form films on the discs, just as they do on teeth. Aftera week of such growth the researchers exposed each disc to one of five treatments everyday for a further seven days. Some were swished around in red wine (a pinot noir, vintage2010) for two minutes. Some were swished in a de-alcoholised version of this wine. Somewere swished in chlorhexidine, some in a 12% solution of ethanol (ie, of the same alcoholicstrength as the wine) and some in plain water. This combination of experiments let DrMoreno-Arribas determine whether wine has antibiofilm properties beyond those bestowedby its alcohol content, and also how well it compares with chlorhexidine.Sadly for oenophiles, chlorhexidine still came out on top.
But wine did well against twoof the five species, F. nucleatum and S. oralis. Intriguingly, in the case of S. oralis the dealcoholised version was even more effective than the full-strength stuff. To find out whichchemicals within the wine were having the desired effect, Dr Moreno-Arribas and her teamadded wine extracts such as flavanols and yeast polysaccharides to the mix and repeatedtheir experiments.
The magic turned out to be provided by a group of chemicals called flavan3-ols.Regrettably, this work does not suggest that a nightly glass of wine is a sensiblesubstitute for a thorough dental brushing before you go to bed. But it might, if pursued, allowan alternative to chlorhexidine mouthwash to be developed—perhaps one that does not havesuch a horrible effect on taste buds (From The Economist, May 31, 2014)70Unit 13. Sex and GenderScript 38.
Behaviour of the sexesThe hormone of laddishnessOestrogen, not testosterone, is what makes a male act like a maleIn all species that practise sexual reproduction, males and females show genderspecific behaviours. These range from the way they mate to the way they defend - or fail todefend - their territory. Both males and females start out with the same template at birth, butthen something acts on the male to masculinise him for life. But nobody knows just how thathappens.It is well known that sex hormones like oestrogen, which is typically seen as a femalehormone, and testosterone, similarly seen as a male one, play a role in shaping the neuralcircuits in the developing brain, and that much of that moulding takes place before birth.
Ithas also been established that testosterone, as well as being a fully functional hormone in itsown right, can be (and often is) converted into oestrogen in the body.Male mice experience a short-lived testosterone surge on the day they are born. It lastsless than 36 hours and the level then remains low until puberty. (In human males, thereappears to be a similar neonatal surge.) This pulse of testosterone is believed to be a keyevent in the masculinization of the brain. Nirao Shah and his colleagues at the University ofCalifornia, San Francisco wanted to find out which neurons in the brain were responding to it.What they discovered was a surprise.
It was reasonable to think, as many people did,that androgen receptors which respond to male hormones were mediating the manlytransformation. But androgen receptors were found to be nearly non-existent in the brains ofnewborn animals. Dr Shah could not find them earlier in development either, such as justafter the fetal testes first started putting out testosterone in a 13-day-old embryo. Withoutmale hormone receptors to respond to testosterone, the researchers started to suspectandrogen receptors were not the players they had been assumed to be. Nor, perhaps, wastestosterone.In their study, published this week in Neuron, the researchers decided to look at malemice which had been genetically engineered to lack androgen receptors in their nervoussystems. These males still had androgen receptors in their muscles and elsewhere, so theyhad masculine bodies, and they experienced the testosterone surge and responded tonormally circulating testosterone.
But their brains were simply not able to detect it.The mice were compared with normal males in tests of masculinity. In one, a femalewas put into the cage. Interestingly, the genetically modified mice still showed the classicmale-mating repertoire: mounting, penetration and ejaculation. But the researchers noted thatthey mounted less often, were less apt to penetrate and did not stick at it for as long as thenormal mice.Another test turned up similar resuits. Typically, a strange male entering another male'scage is met with a fight. Again, the mutant mice behaved appropriately, but they were muchless aggressive, spent less time fighting and they took longer breaks between attacks.The same was found for scent-marking.
Like normal males, the mutant mice urinated invarious spots around their cage (unlike females, who create a single latrine). But theydeposited significantly fewer urine marks than the normal males.Because male-typical behaviours developed as the result of a burst of testosterone, butin the absence of receptors for the hormone, the researchers suspect that the testosterone inthe surge is being converted into oestrogen to carry out the newborn sexual differentiation."Masculinisation of neural pathways in response to the testosterone surge at birth proceedsprimarily under the control of oestrogen," they conclude.
Androgen receptors are not themaster regulators for male behaviours, but rather, the researchers say, a "gain controlmechanism" which amplifies such behaviours - or, when the receptors are absent, dialsladdish behaviour down. (From The Economist, May 1, 2010)71Script 39. Lifespan and the sexesCatching upIn the rich world, men are closing the longevity gap with womenReg Dean, who died on January 5th at the ripe age of 110, was unusual. Centenariansare rare in themselves, of course, but male centenarians particularly so. In Britain, where MrDean lived, five times as many women as men receive the famed card of congratulation fromthe queen when they celebrate their 100th birthdays.That may, however, cease to be the case in the future, for the fact that women tend tolive longer than men, though still true, is less true than it was, and the gap is shrinking - inrich countries, at least - every year.In England and Wales, the biggest peacetime difference between the life expectanciesat birth of the two sexes was 6.3 years.
That was in 1967. It is now 4.1 years, and falling. Inthe early 1980s women who made it to 65, the traditional age of retiremcnt for British men,could expect to live four years longer than their male counterparts. The gap now is less thanthree years, though there is still some way to go before things return to the nine·month gapthat prevailed in the 1840s, when records began. Other industrialised countries, exceptJapan and Russia, show something similar.This trend is superimposed on another: that life expectancy in most developed countrieshas been improving for both sexes.
But of late it has been improving more for men than forwomen. A report about to be published by the Longevity Science Advisory Panel (a group ofscientists and actuaries set up by Legal&General, an insurance company) examines thefactors behind these trends.The biggest by far is changes in the use of tobacco. Around half the difference in thelongevity of the sexes can be explained by smoking. One reason why Russia bucks the trendtowards equal life expectancies for the two sexes (women there live 12 years longer thanmen) is that its men have not followed their Western confreres and cut down on the cancersticks.In Britain in the 1960s, when the habit was commonplace, men were much more likelyto be smokers than women. But they have also been more likely than women to give upcigarettes over the past half-century.
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