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Plastics chemical harms eggs in unborn mice

http://www.newscientist.com/article/dn10946-plastics-chemical-harms-eggs-in-unborn-mice.html

 

Plastics link to 'macho' female mice

 

 

 

14 May 2006 'Oestrogen soup' linked to cancer 16 July 2005 Oral contraception linked to prostate deformities

03 May 2005

 

 

Female mice exposed to a common chemical found in plastics while in the womb develop abnormal eggs, according to a new study. Based on this finding, researchers speculate that the chemical, bisphenol A, might increase the risk of spontaneous abortion and genetic disorders in humans, such as Down's syndrome.

Bisphenol A, or BPA, is commonly found in hard plastics and the lining of tin cans. The chemical has come under scrutiny before because it can mimic the hormone oestrogen.

Patricia Hunt at Washington State University in Pullman, US, and colleagues exposed pregnant mice to 20 micrograms of BPA per kilogram of their bodyweight each day over a one-week period. During this same period, the reproductive cells of female mice developing inside in the womb begin a process of division known as meiosis.

Meiosis ultimately yields mature eggs, which have half the number of chromosomes as other cells in the body. But the process is gradual. In humans, for example, cells only reach the end of this division process before ovulation.

Scrambled eggs

Researchers followed the female mouse pups that had been exposed to BPA in the womb. When these mice reached adulthood, Hunt's team examined their eggs. More than one in every 20 cells taken from those mice had unpaired chromosomes – an abnormal trait. This trait was completely absent in cells taken from the BPA-free control mice.

An analysis of slightly more mature eggs taken from another group of females exposed to BPA in utero found that 10 eggs out of 56 sampled had one or more extra chromosomes than normal. In contrast, only one out of 57 such cells from a control group showed the same defect.

By staining the cells, the researchers found that the chromosomes in eggs from BPA-exposed mice connect in odd places during cell division. This might explain why they do not segregate properly during meiosis.

The embryos of mice exposed to BPA in utero also show abnormalities, suggesting that the chemical affects the grandchildren of exposed mice – a "grandmaternal" impact.

Human concern

Hunt is concerned that BPA might disrupt egg development in humans as well. The types of chromosomal defects seen in her mice are known to increase the risk of spontaneous abortion and genetic disorders such as Down's syndrome.

"It's very concerning," agrees Dorothy Warburton at Columbia University in New York, who was not involved in the study. But she notes that measuring exposure to BPA in humans "is a not an easy thing to do".

The US Environmental Protection Agency has declared that exposure to 50 micrograms or less of BPA per kilogram of bodyweight is safe for humans.

Steve Hentges of the American Plastics Council in Arlington, Virginia, US, stresses that this guideline refers to eating or drinking BPA. He believes that the unborn mice were exposed to higher levels of BPA because they received it through implanted pellets rather than through their food.

For this reason, Hentges argues against drawing conclusions about human health from the study: "These results do not seem to be relevant for reproduction and in particular fertility." He adds that other mouse studies that involved BPA levels similar to those used in Hunt's experiments did not show an increased risk of genetic abnormalities across generations.

However, Hunt is convinced that the BPA amounts used in her study are equivalent to current human exposure. She notes that previous research has found that mice exposed to the chemical in utero have abnormal prostate and breast tissue development that could put them at greater risk of developing cancer in these tissues.

Journal reference: PLoS Genetics (DOI: 10.1371/journal.pgen.0030006)

 

 

Beauty is in the eye of your friends

http://www.newscientist.com/article/dn10966-beauty-is-in-the-eye-of-your-friends.html

 

00:01 17 January 2007 NewScientist.com news service Debora MacKenzie

 

 

 

 

 

 

Enlarge image

Suddenly, the man on the left seems more attractive (Image: Ben Jones et al)

 

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It is a classic image: a group of young women sighing over the latest heartthrob. But do they all really share identical taste for, say, Brad Pitt, or that cute guy in physics class? A new study suggests that, in fact, women will look more favourably on the men that other women find attractive.

Female guppies, quail and finches tend to mate with males that look like the males they have seen other females paired with. Such “mate choice copying” can pay off. If it is difficult to choose the best mating material, or takes a lot of time and energy, it makes sense to go with what works for the other girls.

Yet although human mate selection suffers just such difficulties, there has been little evidence that women do this, until now.

Ben Jones at the University of Aberdeen in Scotland, and colleagues, showed 28 men and 28 women pairs of male faces and asked them to rate their attractiveness. The photos had been already been rated by 40 women as of about equal attractiveness.

Striking difference

The researchers then showed the same faces alongside a third photo of a female face in profile, positioned so she was looking at one of them, and smiling – or not. The viewers were asked to grade the faces again.

Women found the men who were being smiled at suddenly more attractive, while men who apparently elicited no such smiling approval were pronounced less attractive.

Men, meanwhile, behaved in a strikingly different manner. They rated men who had been smiled at as less attractive. ”Within-sex competition promotes negative attitudes towards men who are the target of positive social interest from women,” the researchers conclude.

Or to put it another way, the next time you hear a man say “I don’t know what she sees in him”, remember the fact she’s sees anything at all may be off-putting enough…

Journal reference: Proceedings of the Royal So

 

Instant Expert: Love

 

12:09 04 September 2006 NewScientist.com news service John Pickrell, Lucy Middleton and Alun Anderson

 

 

http://www.newscientist.com/article.ns?id=dn9981

 

 

 

The word love appears in many contexts: there’s maternal love, familial love, romantic love, sexual love, a wider love for fellow humans and religious love for God, to name but a few. Some cultures have ten or more words for different forms of love, and poets and songwriters always find myriad aspects of love to celebrate.

The science of love is still in its infancy. Yet scientists are beginning to get early insights into the nature and origin of love. We can now look inside human brains to view changing patterns of activity and biochemical changes that take place during love, explore diverse human experiences of love, study how we select mates and woo lovers, and look for the evolutionary roots of love.

Addicted to love

So what exactly is going on during the rollercoaster of euphoria and despair that is falling in love?

In the brain, romantic love shows similarities to going mildly insane or suffering from obsessive compulsive disorder. Studies show that when you first fall in love, serotonin levels plummet and the brain's reward centres are flooded with dopamine. This gives a high similar to an addictive drug, creating powerful links in our minds between pleasure and the object of our affection, and meaning we crave the hit of our beloved again and again.

Lust is driven by sex hormones such as testosterone, which can go off-kilter too. As can levels of the stress hormone cortisol, and the amphetamine-like chemical phenylethlyamine, increasing excitement.

Other hormones, oxytocin and vasopressin, kick in later and appear to be crucial for forming long-term partnerships. Couples who have been together for several years show increased brain activity associated with these chemicals, when they look at pictures of their partner. Oxytocin is produced when couples have sex and touch, kiss and massage each other - the hormone makes us more trusting, helps overcome "social fear" and is important for bonding.

Brain scans of people in love show that the old adage "love is blind" really is true. While the dopamine reward areas are excited in love, regions linked with negative emotions and critical social judgement switch off.

Sexual chemistry

Making the right choice when finding true love is an important business, so how do we go about selecting a mate?

Many factors add up to make us desirable to potential partners. There's the obvious stuff like symmetrical features and good skin - which showcase a healthy development, immune system and good genes. Women look for tall men with masculine faces, kindness, wealth and status. Men prefer young, fertile women with a low waist-to-hip ratio and who are not too tall. Neither sex is very keen on people who wear glasses.

Beauty can come at a price however.

Other factors are less obvious. Research suggests that humans are attracted to partners who resemble themselves and - slightly disconcertingly - their parents too. Smell appears to be important as well; people are often more attracted to the smell of those who have different combinations of some immune system (MHC) genes to themselves. Mates with dissimilar MHC genes produce healthier offspring that are better able to thwart disease. People with similar MHC genes even prefer the same perfumes.

Suitors of some species such as birds, and even mice, attract their mates with complex songs or showy displays. Intelligence and talent are prized by people too. As are expensive gifts and even cheap love tokens. Even being in a relationship can make you more attractive to potential mates.

Other factors are more random - a woman's attractiveness and pheromones can fluctuate with her hormone levels and menstrual cycle. As a consequence, taking the pill can inhibit a woman's ability to select an appropriate mate.

In concert, these many factors mean the path to true love can be somewhat unpredictable.

Many people with hectic lifestyles today are turning to the internet, online lonely hearts, dating websites and speed dating to help them track down a partner. Love by wire may have started much longer ago however. See here for six tips to woo your lover.

Love evolution

The various forms of love probably have a common evolutionary beginning, so where are scientists looking? Maternal love seems a good place to start. Biologically it makes perfect sense. In animals which help their offspring to survive, the bond is essential to passing the mother’s genes on to the next generation.

Again oxytocin may have an important role in the development of a bond between a mother and child. Another hormone, prolactin, may prime both mothers and fathers for parenthood.

Unlike maternal love, monogamous bonds between males and females are pretty rare in mammals. Less than 5% are monogamous, and there is no clear pattern to help explain why it occasionally appears. Monogamy, it appears, is mostly for the birds.

It seems that in those rare mammals that do practise it, evolution stole the biochemistry and neural tricks that bond mother to infant and reinstalled them, so as to bind male and female together. One study of prairie voles shows that a species could be turned from promiscuous to devoted with a change in a single gene related to vasopressin.

Whatever romantic love's origins and purpose, long-term relationships are certainly important in keeping us content and happy.

And love is not only restricted to partnerships between men and women. Though gay relationships are different in some ways, they could be the glue that holds societies together.

Heart-breaking

Unfortunately, it's not all wine and roses when it comes to love. Ecstasy, euphoria, elation and contentment may be accompanied by jealousy, rage, rejection, and hatred.

Falling in love may have evolved because people who focus their attention on a single ideal partner save time and energy, therefore improve their chances of survival and reproduction. Unfortunately, this also means people are pre-disposed to terrible suffering when jilted by their beloved.

Painful emotions develop when the reward centres of the brain, associated with the dopamine high of falling in love, fail to get their hit. Paradoxically when we get dumped we tend to love back even harder, as the brain networks and chemicals associated with love increase. First we protest and attempt to win the beloved back. Panic also kicks in as we feel something akin to the separation anxiety experiences by young mammals abandoned by their mothers.

Then love can turn to anger and hate, as the regions associated with reward are closely linked to rage in the brain. Finally when jilted lovers are resigned to their fate, they will often enter into prolonged periods of depression and despair.

These negative emotions can spawn anything from obsession and domestic violence to stalking and even murder of supposed loved ones.

While such behaviours may be classed as pathological, and perhaps rare, the truth is that they are closer to home than we dare contemplate. Passion’s thrills resemble obsessive-compulsive disorder, but in some people, love can conjure up something much more sinister.

The chances of a relationship succeeding would seem to be difficult to predict, but one study suggests that divorce may be partially genetically predetermined. There are even mathematical formulas for predicting the chances of divorce - and for equitably dividing up possessions.

Nevertheless, psychologists have some simple tips for making our relationships last.