Chapter 8. Hormones and Sex
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By Scicurious We’ve all heard of the legendary monogamous prairie vole, haven’t we? Our adorable rodent friend forms the kind of attachments that make us humans feel slightly ashamed of our more promiscuous habits. And of course, if we know about prairie voles, we know about oxytocin (and I’ve got a whole series on it over at the ‘Science! 101′ page of my other site). Prairie voles are monogamous primarily due to the actions of oxytocin in the female, and vasopressin in the male. Without these two hormones, the prairie voles will love ‘em and leave ‘em just like their close cousins, the meadow vole. But is that all there really is to pair bonding? Just one hormone, a desire to stay with your furry mate forever…and that’s it? No, it’s more complicated than that. There are two real aspects to a pair bond. The first is the prosocial bit, the animal preferring to associate with one particular other animal. In voles, this requires the hormones oxytocin and vasopressin, and the neurotransmitter dopamine. But there’s another aspect to pair bonding: maintenance. And that requires more than fuzzy feelings, it also requires rejection of other potential mates, and guarding your mate against all comers. This aggressive behavior also involves dopamine, but in this case, a different population of receptors. © 2012 Scientific American
By Daisy Yuhas How do I love thee? When neuroscientist Young and journalist Alexander started counting, they found many molecular ways. In The Chemistry between Us, the writers highlight the complex chemical processes that create love in the brain and bolster the argument that love is an addiction. Young has devoted his career to studying the behaviors and neural circuitry of love in the prairie vole, a rodent whose monogamous tendencies resemble our own. Once a prairie vole has found “the one,” the pair will most likely remain companions for life. Young's research has implicated a range of chemical activities—mainly during sex—that build this lifelong bond. In particular, he uncovered how two hormones in the brain, vasopressin in male voles and oxytocin in female voles, regulate social behavior and memory—promoting the recognition of a loved one and the urge to cuddle or defend. In addition, the circulation of dopamine and opioids allows the vole to associate his or her partner with pleasure, thus strengthening their bond. Many of these molecules are identical to those activated in human bonding. That loving feeling comes at a price. A hormone called corticotropin-releasing factor, or CRF, builds up in the brains of paramours and parents alike. The CRF system activates a stress response, and this system elicits the painful sensations you feel when your baby cries or your boyfriend dumps you. The system may seem like a nasty trick, but it has its uses. Even when passion fades or a diaper needs changing, the sharp pangs of the CRF system keep families and loved ones together. The CRF system also contributes to the agony an addict feels after the elation wears off. Thus, the authors argue, the highs of intimacy and withdrawals of separation parallel the highs and lows that drug addicts experience. © 2012 Scientific American
Steve Connor Babies of older fathers are more likely to carry genetic mutations than those of younger fathers. And the mutations could lead to illnesses such as autism and schizophrenia in later life, a landmark study has shown. Scientists have, for the first time, counted the number of new mutations linked with a father's age at the time of conception and have concluded that older men are significantly more likely to have children with potentially harmful genetic changes. The results could explain previous studies showing that certain mental and developmental illnesses with strong genetic components tend to be more common among people whose fathers were older at the time of conception. Although the age of a child's mother has been linked with problems associated with chromosomal defects, such as Down's syndrome, there has been scant information about the contribution made by older fathers to the future health of their offspring. "These observations shed light on the importance of the father's age on the risk of diseases such as schizophrenia and autism," the researchers say in their study published in the journal Nature. The scientists found that a new-born baby's genome contains around 60 new small-scale mutations compared with its parents and that the actual number of new mutations carried by each child was strongly dependent on the age of the father, rather than the mother, at the time of conception. The researchers, led by Augustine Kong and Kari Stefansson of deCode Genetics in Reykjavik, calculated that a 20-year-old father transmits about 25 new mutations to his child while a 40-year-old man will pass on 65. © independent.co.uk
Kathryn Lougheed A chemical in llama semen responsible for inducing ovulation in females has been identified and, surprisingly, it is a protein already known for its role in promoting the growth and survival of nerve cells in many species1. The protein — nerve growth factor (NGF) — is also found in human semen, suggesting that it may play a previously unsuspected role in human fertility. Whereas many animals, including humans, cattle and mice, produce eggs as part of a cycle of spontaneous ovulation, others — including llamas, camels, rabbits and koalas — are ‘induced ovulators’ that need a chemical stimulus. In 2005, Gregg Adams, a veterinary surgeon and reproductive scientist at the University of Saskatchewan in Saskatoon, Canada, and his colleagues showed that in llamas, the stimulus was in the seminal fluid2. In the latest study, published this week in the Proceedings of the National Academy of Sciences1, Adams led a team that identified the chemical as NGF. Although human women do not require NGF in semen to ovulate, Adams says that the protein could still have a direct effect on human fertility. Earlier this year, he published a paper3 showing that llama seminal fluid shortens the ovulation cycles of cows and seems to stimulate the development of the corpus luteum — a structure inside the ovaries that forms after an egg has been released and secretes hormones vital to pregnancy. In some cases, NGF could explain why some couples find it difficult to conceive, says Adams. A couple could have fertility problems if either the man failed to produce enough NGF in his semen or the woman lacked the receptors to detect and respond to it, he says. © 2012 Nature Publishing Group
Keyword: Sexual Behavior
Link ID: 17187 - Posted: 08.22.2012
By Brett Israel and Environmental Health News A widely used pesticide – banned in homes but still commonly used on farms – appears to harm boys’ developing brains more than girls’, according to a new study of children in New York City. In boys, exposure to chlorpyrifos in the womb was associated with lower scores on short-term memory tests compared with girls exposed to similar amounts. The study is the first to find gender differences in how the insecticide harms prenatal development. Scientists say the finding adds to evidence that boys’ brains may be more vulnerable to some chemical exposures. “This suggests that the harmful effects of chlorpyrifos are stronger among boys, which indicates that perhaps boys are more vulnerable to this type of exposure,” said Virginia Rauh, a perinatal epidemiologist at Columbia University and co-author of the study published in July. Chlorpyrifos is an organophosphate insecticide, a powerful class of pesticide that has toxic effects on nervous systems. It was widely used in homes and yards to kill cockroaches and other insects, but in 2001 the U.S. Environmental Protection Agency banned its residential use because of health risks to children. Since then, levels inside U.S. homes have dropped [PDF], but residue remains in many homes. In addition, many developing countries still use the pesticide indoors. Known by the Dow trade name Lorsban, chlorpyrifos is still sprayed on some crops, including fruit trees and vegetables, and also is used on golf courses and for mosquito control. About 10 million pounds of chlorpyrifos are applied to agricultural fields annually, according to the EPA. © 2012 Scientific American,
By Jonathan Ball BBC News Young male fruit flies learn the smell of a receptive female to avoid wasting their sexual efforts, research shows. Promiscuous male flies initially court all females, but are rejected by those who have already mated. It is clear that the flies eventually learn to spot mated females, but just how they do has remained a mystery. Research published in Nature suggests that they smell a chemical signal called a pheromone left by other males during mating. The studies were performed using the common fruit fly - Drosophila melanogaster. This insect is used widely in genetic studies because they are easy to grow and they reproduce quickly - but principally because it is possible to generate and study flies that possess changes - or mutations - in their genetic material. In the study, Prof Barry Dickson and colleagues from the Research Institute of Molecular Pathology in Vienna, Austria, performed a series of studies to identify the mechanism that led to this change in behaviour in older flies. Using complementary approaches, the team showed that a pheromone called cVA was responsible. Pheromones are substances produced by one individual which modify the behaviour of another. They are widely known to work in the animal kingdom to warn of danger, define territories or attract mates. Mosquito The finding could be used for the control of other insects such as mosquitoes, which spread malaria BBC © 2012
Sleep apnea, a disorder characterized by snoring and daytime sleepiness that has been linked to cardiovascular disease, has primarily been viewed as a male problem, but a new Swedish study suggests the sleep disorder is also a common problem among women. Dr. Karl A Franklin of Umea University Hospital in Sweden and colleagues noted in the study released Wednesday that there have been only a few epidemiological studies conducted in women, and the frequency of the disorder in women "is still uncertain." Obstructive sleep apnea, in which a person has short pauses in breathing during sleep, may be caused by a temporary collapse of the airway. The gaps in breathing can last 10 to 30 seconds, and may occur dozens or hundreds of times each night. For their study, Franklin and the other Swedish researchers investigated 400 women from a population-based random sample of 10,000 women aged 20 to 70. The women answered a questionnaire and were monitored overnight. Obstructive sleep apnea was found in 50 per cent of the women subjects, with 14 per cent of them having a severe form of the disorder. Treatment for obstructive sleep apnea: For mild to moderate apnea, the best treatment is continuous positive airway pressure (CPAP). © CBC 2012
Link ID: 17170 - Posted: 08.16.2012
by Michael Slezak A lack of anti-Müllerian hormone in boys with autistic spectrum disorder (ASD) may lead to a greater number of symptoms. Michael Pankhurst and Ian McLennan from the University of Otago in New Zealand say hormones like anti-Müllerian hormone (AMH) that control the speed at which the body and brain develop might play a central role in the way that ASD progresses through childhood. The pair analysed the level of AMH in 82 boys with ASD. The lower the level of AMH in their blood, the greater the number of autistic traits they displayed. In an earlier study, McLennan and his colleagues found that an increased level of AMH was associated with slower overall growth and development in boys. Together, he thinks the two studies suggest that a lack of AMH could cause the brain to develop too quickly, leading to an increased number of symptoms in boys with ASD. "Rapid development is associated with a greater frequency of developmental disorders," says McLennan. A complex system that develops quickly is more likely to contain errors than one that develops more slowly, he explains. Surprisingly, there was no difference between the average level of anti-Müllerian hormone in the children with ASD and 16 boys without autism. McLennan says this shows that the hormone doesn't cause ASD, but may increase the number of symptoms in people who have the condition. © Copyright Reed Business Information Ltd.
By ABBY ELLIN After downing 70 chicken wings in about an hour, Andrew Walen realized he had a problem. Oh, he had known something was wrong over the years. Normal people don’t consume 4,500 calories worth of food in one sitting, or order takeout for four when dining alone. But it took a maniacal feeding frenzy for him to finally accept the reality: He was a binge eater, and he had absolutely no control around food. “Ultimately, it was about numbing out and self-loathing,” said Mr. Walen, now 39 and a therapist in Columbia, Md. “There was this voice in my head that said, ‘You’re no good, worthless,’ and I turned to food.” Mr. Walen is one of an estimated eight million men and women in the United States who struggle with binge eating, defined as consuming large amounts of food within a two-hour period at least twice a week without purging, accompanied by a sense of being out of control. While about 10 percent of patients with anorexia and bulimia are men, binge eating is a problem shared almost equally by both sexes. A study published online in October and then in the March issue of The International Journal of Eating Disorders found that among 46,351 men and women ages 18 to 65, about 11 percent of women and 7.5 percent of men acknowledged some degree of binge eating. “Binge eating among men is associated with significant levels of emotional distress, obesity, depression and work productivity impairment,” said Richard Bedrosian, a study author and director of behavioral health and solution development at Wellness and Prevention Inc., which works with employers and health plans. Copyright 2012 The New York Times Company
by Carol Cruzan Morton Migraines are a battle of the sexes that women might prefer not winning. Each year, roughly three times more women than men—up to 18% of all women—suffer from the debilitating headaches, as tallied by epidemiological surveys in Europe and the United States. A new brain imaging study may explain the divide: The brains of women with migraines appear to be built differently than those of their male counterparts. To conduct the study, researchers headed by David Borsook, a neurologist and neurobiologist of Boston Children’s Hospital and Harvard Medical School, recruited 44 men and women, half of whom were migraine sufferers. The women who had migraines rated them as being as intense as the men did, but they tended to find them more unpleasant. Borsook says the distinction is analogous to the loudness of fingernails scratching on a chalkboard versus the torment of hearing the sound. The team then scanned the brains of the volunteers. The researchers gathered two kinds of data sets, one that captured brain shapes and features, and one that measured brain activity. Female migraine sufferers showed slightly thicker gray matter in two regions: one, the posterior insula, is well-known in pain processing; the other, the precuneus, has been recently linked to migraines but is more widely known as a fundamental brain hub that may house a person's consciousness or sense of self. The other volunteers, including the male migraine sufferers, did not show this thickening. All of the scans were done when people did not have a migraine. To figure out what those structural changes meant, lead author Nasim Maleki, a medical physicist at Boston Children's Hospital and Harvard Medical School, returned to the MRI scans of only those men and women with episodic migraines. © 2010 American Association for the Advancement of Science.
By RUTH PADAWER The night before Susan and Rob allowed their son to go to preschool in a dress, they sent an e-mail to parents of his classmates. Alex, they wrote, “has been gender-fluid for as long as we can remember, and at the moment he is equally passionate about and identified with soccer players and princesses, superheroes and ballerinas (not to mention lava and unicorns, dinosaurs and glitter rainbows).” They explained that Alex had recently become inconsolable about his parents’ ban on wearing dresses beyond dress-up time. After consulting their pediatrician, a psychologist and parents of other gender-nonconforming children, they concluded that “the important thing was to teach him not to be ashamed of who he feels he is.” Thus, the purple-pink-and-yellow-striped dress he would be wearing that next morning. For good measure, their e-mail included a link to information on gender-variant children. When Alex was 4, he pronounced himself “a boy and a girl,” but in the two years since, he has been fairly clear that he is simply a boy who sometimes likes to dress and play in conventionally feminine ways. Some days at home he wears dresses, paints his fingernails and plays with dolls; other days, he roughhouses, rams his toys together or pretends to be Spider-Man. Even his movements ricochet between parodies of gender: on days he puts on a dress, he is graceful, almost dancerlike, and his sentences rise in pitch at the end. On days he opts for only “boy” wear, he heads off with a little swagger. Of course, had Alex been a girl who sometimes dressed or played in boyish ways, no e-mail to parents would have been necessary; no one would raise an eyebrow at a girl who likes throwing a football or wearing a Spider-Man T-shirt. © 2012 The New York Times Company
by Sara Reardon Freedom of information requests have revealed that pregnant women may not have been given all the facts before taking an experimental treatment to prevent female fetuses from being masculinised as a result of a rare genetic disorder. Research has provided some evidence that dexamethasone, a drug normally prescribed to relieve inflammation, can prevent girls with a rare hormonal disease from developing male genitalia and same-sex attraction if they are treated as fetuses. But as yet, no clinical studies show that this treatment is safe, says Alice Dreger of Northwestern University in Evanston, Illinois. She claims that researchers have misled an unknown number of pregnant women into taking the experimental treatment without properly informing them of its risks. Since the 1980s, Maria New of Mount Sinai School of Medicine in New York has studied and popularised the idea of prescribing dexamethasone "off-label" to women at risk of having foetuses with congenital adrenal hyperplasia (CAH). The treatment is now taught as standard practice in medical schools. But because the drug must be given very early in pregnancy before the fetus' gender or CAH status is known, many fetuses are treated unnecessarily. A child with two carrier parents has a one-in-four chance of having the disease, and the treatment only works for girls. There is little research available on the effects of dexamethasone, which mimics a steroid hormone. And because dexamethasone doesn't cure CAH but only prevents masculinisation of girls, it can be difficult to distinguish possible effects of the drug from other treatments the children receive after birth. © Copyright Reed Business Information Ltd.
by Michael Marshall You may think you can cope without sleep, but you have nothing on male pectoral sandpipers. Some of these birds can go more than a fortnight with hardly any sleep – the most extreme case of uninduced sleep deprivation known in any animal. What's more, the males that sleep the least father the most offspring, suggesting they benefit from their lack of slumber. Pectoral sandpipers (Calidris melanotos) breed on the Arctic tundra of Asia and North America. Males don't help with childcare – instead they try to mate with as many females as possible. Bart Kempenaers of the Max Planck Institute for Ornithology in Seewiesen, Germany and colleagues fitted radio tags to 149 birds – accounting for most of a population living near Barrow in Alaska. This showed that males were highly active during periods when females were fertile. One male was active 95 per cent of the time for 19 days. The team then fitted 29 of the males with devices that recorded their brain activity, something never done before with a wild bird. This allowed them to look at the active males' sleep patterns. They found that the males that slept the least slept more deeply, but calculations show that this wouldn't make up for the sleep they missed, says team member Niels Rattenborg. © Copyright Reed Business Information Ltd
By Stephanie Pappas Senior Writer For women looking to pass on their genes, it pays to be short. For men, tall is the ideal. The result? An evolutionary tug-of-war in which neither gender reaches their perfect height. Those are the results of a new study published Aug. 7 in the journal Biology Letters. The research finds that an evolutionary battle of the sexes keeps the genders in an endless feedback loop of height variations across the generations. "We should not simply assume that when a trait is beneficial for one sex, that selection or evolution will necessarily favor this trait," study researcher Gert Stulp, a scientist at the University of Groningen in the Netherlands, told LiveScience in an email. In the same way, traits that harm one sex but not the other may not be "weeded out" by natural selection, Stulp said. "This may even hold for health-related traits, such that genetic underpinnings beneficial to the health of one sex may increase the susceptibility to disease in the other sex," he said. In modern western societies, studies have found that women who are on the short side tend to have more children. In contrast, average-height men do the best, reproductively speaking, outpacing short and tall men in number of children fathered, Stulp said. © 2012 NBCNews.com
By Scicurious Our brains are made of millions of neurons. Tons. A lot. We scientists spend a lot of time studying those neurons, how they function individually, and how they respond to outside stimulation. But neurons cannot function alone. What sets a neuron apart is its ability to carry electric signals and to transfer chemical signals to other neurons. The function of neurons is not in the neurons themselves, it is in the connection between them. And this incredibly complicated network, composed of billions of connections, is called the connectome. If we knew the connectome of the human, we’d know a lot more about the brain than we do now. We are learning it, little by little, but with a series of connections that are so incredibly vast, it’s just too much right now to examine every single possible connection. Right now the only way to ensure getting every single connection in painstaking detail is to use electron microscopy to view synapses, the connections between neurons. Concentrations of the little organelles which signify a synapse (such as vesicles full of neurotransmitter), can tell you where each connection is placed. But the electron microscope can only look at a very small section at a time, making the mapping of a connectome an incredibly arduous task. C. elegans, to be exact. The nematode is a darling of basic research, and for a very good reason. C. elegans is incredibly simple, having exactly 302 neurons in the entire body. Well, 302, or 383. There are two kinds of C. elegans, hermaphrodite and male (there are no females). The males mate with the hermaphrodites. But this means that the male C. elegans is slightly different from the hermaphrodite C. elegans. While the hermaphrodite has 302 neurons, the male has 383. And most of these appear to be devoted to a complex series of behaviors characteristic of mating. © 2012 Scientific American,
By Susan E. Matthews The way people's pupils react when they see other people is an effective way to assess sexual orientation, according to a new study. The reactions of study participants' pupils revealed that heterosexual men responded most to images of women and homosexual men responded most to images of men. Additionally, researchers found that homosexual women responded most to images of women, and heterosexual women expressed arousal in response to both men and women, though they were more likely to choose to watch men. Previous studies have shown that people's pupils widen in response to seeing others who they find attractive; the new study showed that, indeed, a person's sexuality is evident in their pupils' responses. Results also revealed that bisexual men were attracted to both men and women, an idea that has been disputed, and that heterosexual women may be aroused by both genders, despite being straight. "The pupil reacts very quickly, and it is unconscious, so it's a method that gives us a subconscious indicator of sexuality," said lead study author Gerulf Rieger, a researcher at Cornell University. Sex researchers don't always want to rely on people's own reports about who they are sexually attracted to, because cultural and societal pressures can influence what people say, he explained. The findings are detailed today (Aug. 3) in the journal PLoS ONE. © 2012 NBCNews.com
by Will Ferguson Let's face it, child rearing isn't for everyone. Midnight diaper changes, a seriously compromised social life, and trading in the two-seater coupe for a mid-size sedan can be too much for some of us to handle. Readers who find themselves in this category might be reassured to know there's at least one other creature on the planet that is, in all likelihood, even more keen to shirk parental responsibility. The common cuckoo is notorious for pawning off its young on other birds, like the Eurasian Reed Warbler (Acrocephalus scirpaceus). Unfortunately for these more willing caregivers, the cuckoo is a ruthless parasite. Upon hatching, young cuckoos push their surrogate brothers and sisters from the nest, leaving the unsuspecting host with a single cuckoo chick rather than a brood of its own. For obvious reasons, reed warblers have never been happy with the arrangement. They will attack female cuckoos on sight, reducing the chance of their nest being targeted. However, the sly cuckoo has developed an innovative way to avoid hostilities. Female cuckoos have evolved two different guises to minimise the chance of being recognised and attacked by warblers. It's unusual for female birds of a single species to come in different colours, but the phenomenon is surprisingly common for female cuckoos. Some are brownish-red, while others have grey, hawk-like plumage that deters other birds from attacking them. © Copyright Reed Business Information Ltd.
By Michael Slezak, Even though women live longer than men, their brains seem to age faster. The reason? Possibly a more stressful life. As people age, some genes become more active while others become less so. In the brain, these changes can be observed through the transcriptome, a set of RNA molecules that indicate the activity of genes within a population of cells. When Mehmet Somel, a computational biologist at the University of California at Berkeley, and his colleagues compared the transcriptome of 55 brains, they found that the pattern of gene activation and deactivation that occurs with aging appeared to progress faster in women. “This was just the opposite of what we’d originally expected,” says Somel. He says that because women have longer lives, his group had expected to see slower or later aging-related brain changes. “But it fits everyday observations on aging. Not all organs within an individual age at the same rate.” Somel’s team compared the expression of more than 13,000 genes in four brain regions. In the superior frontal gyrus, which has been associated with self-awareness, the researchers found 667 genes that were expressed differently in men and women. Of those, 98 percent were skewed toward faster aging in women. Some of these gene changes have been linked to general cognitive decline and degenerative disease. © 1996-2012 The Washington Post
Scientists believe they have discovered a clue to why women tend to live longer than men - by studying fruit flies. Writing in Current Biology, they focus on mutations in mitochondrial DNA - the power source of cells. Mitochondria are inherited only from mothers, never from fathers, so there is no way to weed out mutations that damage a male's prospects. But one ageing expert said there were many factors that explained the gender difference in life expectancy. By the age of 85, there are approximately six women for every four men in the UK, and by 100 the ratio is more than two to one. And females outlive males in many other species. In the research, experts from Australia's Monash University and the UK's Lancaster University analysed the mitochondria of 13 different groups of male and female fruit flies. Mitochondria, which exist in almost all animal cells, convert food into the energy that powers the body. Dr Damian Dowling, of Monash University who was one of the researchers, said the results point to numerous mutations within mitochondrial DNA that affect how long males live, and the speed at which they age. "Intriguingly, these same mutations have no effects on patterns of ageing in females," he said. BBC © 2012
by Michael Slezak Despite the fact that women live longer than men, their brains seems to age faster. The reason? Possibly a more stressful life. When people age, some genes become more active while others become less so. In the human brain, these changes can be observed through the "transcriptome" – a set of RNA molecules that indicate the activity of genes within a population of cells. When Mehmet Somel, a computational biologist at the University of California, Berkeley, and his colleagues compared the transcriptome of 55 male and female brains of different ages, they were surprised to find that the pattern of gene activation and deactivation that occurs with ageing appeared to progress faster in women than in men. This was particularly apparent in an area of the pre-frontal cortex. "This was just the opposite of what we'd originally expected," says Somel, who was at the Shanghai Institutes for Biological Sciences in China when he did the research. He says that given the fact that females have a longer lifespan, they had expected to see slower or later ageing-related changes in their brain. "But it fits everyday observations on ageing. Not all organs within an individual age at the same rate," he says. Somel's team compared the expression of more than 13,000 genes in four brain regions. In one region – the superior frontal gyrus – they found 667 genes that were expressed differently in men and women during ageing. Of those, 98 per cent were skewed towards faster ageing in women. Some of these gene changes have previously been linked to general cognitive decline and degenerative disease. © Copyright Reed Business Information Ltd