Posts tagged testosterone
Articles and news from the latest research reports.
Testosterone in Healthy Men Increases Their Brains’ Response to Threat
Testosterone, a steroid hormone, is well known to contribute to aggressive behavior in males, but the neural circuits through which testosterone exerts these effects have not been clear.
Prior studies found that the administration of a single dose of testosterone influenced brain circuit function. Surprisingly, however, these studies were conducted exclusively in women.
Researchers, led by Dr. Justin Carré, sought to rectify this gap by conducting a study of the effects of testosterone on the brain’s response to threat cues in healthy men.
They focused their attention on brain structures that mediate threat processing and aggressive behavior, including the amygdala, hypothalamus, and periaqueductal gray.
The researchers recruited 16 healthy young male volunteers, who completed two test days on which they received either testosterone or placebo. On both testing days, the men first received a drug that suppressed their testosterone. This step ensured that testosterone levels were similar among all study participants. The amount of testosterone administered in this study only returned testosterone levels to the normal range. Subjects then completed a face-matching task while undergoing a functional magnetic resonance imaging scan.
Data analyses revealed that, compared with placebo, testosterone increased reactivity of the amygdala, hypothalamus and periaqueductal grey when viewing angry facial expressions.
"We were able to show for the first time that increasing levels of testosterone within the normal physiological range can have a profound effect on brain circuits that are involved in threat-processing and human aggression," said Carré, Assistant Professor at Nipissing University.
"Understanding testosterone effects on the brain activity patterns associated with threat and aggression may help us to better understand the ‘fight or flight’ response in males that may be relevant to aggression and anxiety," commented Dr. John Krystal, Editor of Biological Psychiatry.
Expanding our knowledge of exactly how testosterone affects the male brain is particularly important, as testosterone augmentation has become increasingly promoted and aggressively marketed as a solution to reduced virility in aging men. Further work is indeed continuing, Carré said. “Our current work is examining the extent to which a single administration of testosterone influences aggressive and competitive behavior in men.”
(Source: elsevier.com)
More left-handed men are born during the winter
Men born in November, December or January are more likely of being left-handed than during the rest of the year. While the genetic bases of handedness are still under debate, scientists at the Faculty of Psychology, University of Vienna, obtained indirect evidence of a hormonal mechanism promoting left-handedness among men. Psychologist Ulrich Tran and his colleagues published their findings in the scientific journal “Cortex”.
Various manual tasks in everyday life require the use of the right hand or are optimized for right-handers. Around 90 percent of the general population is right-handed, only about 10 percent is left-handed. The study of Ulrich Tran, Stefan Stieger, and Martin Voracek comprised two large and independent samples of nearly 13000 adults from Austria and Germany. As in modern genetic studies, where a discovery-and-replication-sample design is standard, the use of two samples allowed testing the replicability and robustness of findings within one-and-the-same study. Overall, 7.5 percent of women and 8.8 percent of men were left-handed. “We were surprised to see that this imbalance was caused by more left-handed men being born specifically during November, December, and January. On a monthly average, 8.2 percent of left-handed men were born during the period February to October. During November to January, this number rose to 10.5 percent”, according to Ulrich Tran, lead author of the study.
A hormonal cause during embryonic development
"Presumably, the relative darkness during the period November to January is not directly connected to this birth seasonality of handedness. We assume that the relative brightness during the period May to July, half a year before, is its distal cause", explains Ulrich Tran. A theory, brought forth in the 1980s by US neurologists Norman Geschwind and Albert Galaburda, posits that testosterone delays the maturation of the left brain hemisphere during embryonic development. The left brain hemisphere is dominant among right-handers, the right brain hemisphere is dominant among left-handers. Intrauterine testosterone levels are higher in the male fetus, because of its own testosterone secretion, than in the female fetus. However, the testosterone level of the mother and external factors may also affect intrauterine testosterone levels. Specifically, more daylight may increase testosterone levels, making a seasonality effect plausible.
Previous studies on the subject provided mixed and inconsistent evidence. There was no clear indication which season has an effect, and whether seasonality affects men, women or both sexes equally. According to the current findings, there is a small, but robust and replicable, effect of birth seasonality on handedness, affecting only men. These results are consistent with a hormonal basis of handedness, corroborating thus an old and controversial theory. However, the exact way of causation needs to be investigated in future studies.
(Source: medienportal.univie.ac.at)
Children with autism have elevated levels of steroid hormones in the womb
Children who later develop autism are exposed to elevated levels of steroid hormones (for example testosterone, progesterone and cortisol) in the womb, according to scientists from the University of Cambridge and the Statens Serum Institute in Copenhagen, Denmark. The finding may help explain why autism is more common in males than females. However, the researchers caution it should not be used to screen for the condition.
The team of researchers, led by Professor Simon Baron-Cohen and Dr Michael Lombardo in Cambridge and Professor Bent Nørgaard-Pedersen in Denmark, utilized approximately 19,500 amniotic fluid samples stored in a Danish biobank from individuals born between 1993-1999. Amniotic fluid surrounds the baby in the womb during pregnancy and is collected when some women choose to have an amniocentesis around 15-16 weeks of pregnancy. This coincides with a critical period for early brain development and sexual differentiation, and thus allows scientists access into this important window in fetal development. The researchers identified amniotic fluid samples from 128 males later diagnosed with an autism spectrum condition and matched these up with information from a central register of all psychiatric diagnoses in Denmark.
Within the amniotic fluid the researchers looked at four key ‘sex steroid’ hormones that are each synthesized, step-by-step from the preceding one*. They also tested the steroid hormone cortisol that lies outside this pathway. The researchers found that levels of all steroid hormones were highly associated with each other and most importantly, that the autism group on average had higher levels of all steroid hormones, compared to a typically developing male comparison group. The results of the study, which was funded by the Medical Research Council, are published today in the journal Molecular Psychiatry.
Professor Baron-Cohen said: “This is one of the earliest non-genetic biomarkers that has been identified in children who go on to develop autism. We previously knew that elevated prenatal testosterone is associated with slower social and language development, better attention to detail, and more autistic traits. Now, for the first time, we have also shown that these steroid hormones are elevated in children clinically diagnosed with autism. Because some of these hormones are produced in much higher quantities in males than in females, this may help us explain why autism is more common in males.”
He added: “These new results are particularly striking because they are found across all the subgroups on the autism spectrum, for the first time uniting those with Asperger Syndrome, classic autism, or Pervasive Developmental Disorder Not-Otherwise-Specified. We now want to test if the same finding is found in females with autism.”
Dr Michael Lombardo said: “This result potentially has very important implications about the early biological mechanisms that alter brain development in autism and also pinpoints an important window in fetal development when such mechanisms exert their effects.”
Steroid hormones are particularly important because they exert influence on the process of how instructions in the genetic code are translated into building proteins. The researchers believe that altering this process during periods when the building blocks for the brain are being laid down may be particularly important in explaining how genetic risk factors for autism get expressed.
Dr Lombardo adds: “Our discovery here meshes nicely with other recent findings that highlight the prenatal period around 15 weeks gestation as a key period when important genetic risk mechanisms for autism are working together to be expressed in the developing brain.”
Professor Baron-Cohen said: “These results should not be taken as a reason to jump to steroid hormone blockers as a treatment as this could have unwanted side effects and may have little to no effect in changing the potentially permanent effects that fetal steroid hormones exert during the early foundational stages of brain development.”
He cautioned further: “Nor should these results be taken as a promising prenatal screening test. There is considerable overlap between the groups and our findings showed differences found at an average group level, rather than at the level of accurately predicting diagnosis for individuals. The value of the new results lies in identifying key biological mechanisms during fetal development that could play important roles in atypical brain development in autism.”
*Within the amniotic fluid the researchers looked at 4 key ‘sex steroid’ hormones that are each synthesized, step-by-step from the preceding one, in the ‘Δ4 sex steroid’ pathway: progesterone, 17α-hydroxy-progesterone, androstenedione and testosterone.
Sudden Decline in Testosterone May Cause Parkinson’s Disease Symptoms in Men
The results of a new study by neurological researchers at Rush University Medical Center show that a sudden decrease of testosterone, the male sex hormone, may cause Parkinson’s like symptoms in male mice. The findings were recently published in the Journal of Biological Chemistry.
One of the major roadblocks for discovering drugs against Parkinson’s disease is the unavailability of a reliable animal model for this disease.
“While scientists use different toxins and a number of complex genetic approaches to model Parkinson’s disease in mice, we have found that the sudden drop in the levels of testosterone following castration is sufficient to cause persistent Parkinson’s like pathology and symptoms in male mice,” said Dr. Kalipada Pahan, lead author of the study and the Floyd A. Davis endowed professor of neurology at Rush. “We found that the supplementation of testosterone in the form of 5-alpha dihydrotestosterone (DHT) pellets reverses Parkinson’s pathology in male mice.”
“In men, testosterone levels are intimately coupled to many disease processes,” said Pahan. Typically, in healthy males, testosterone level is the maximum in the mid-30s, which then drop about one percent each year. However, testosterone levels may dip drastically due to stress or sudden turn of other life events, which may make somebody more vulnerable to Parkinson’s disease.
“Therefore, preservation of testosterone in males may be an important step to become resistant to Parkinson’s disease,” said Pahan.
Understanding how the disease works is important to developing effective drugs that protect the brain and stop the progression of Parkinson’s disease. Nitric oxide is an important molecule for our brain and the body.
"However, when nitric oxide is produced within the brain in excess by a protein called inducible nitric oxide synthase, neurons start dying,” said Pahan.
“This study has become more fascinating than we thought,” said Pahan. “After castration, levels of inducible nitric oxide synthase (iNOS) and nitric oxide go up in the brain dramatically. Interestingly, castration does not cause Parkinson’s like symptoms in male mice deficient in iNOS gene, indicating that loss of testosterone causes symptoms via increased nitric oxide production.”
“Further research must be conducted to see how we could potentially target testosterone levels in human males in order to find a viable treatment,” said Pahan.
Other researchers at Rush involved in this study were Saurabh Khasnavis, PhD, student, Anamitra Ghosh, PhD, student, and Avik Roy, PhD, research assistant professor.
This research was supported by a grant from the National Institutes of Health that received the highest score for its scientific merit in the particular cycle it was reviewed.
Parkinson’s is a slowly progressive disease that affects a small area of cells within the mid-brain known as the substantia nigra. Gradual degeneration of these cells causes a reduction in a vital chemical neurotransmitter, dopamine. The decrease in dopamine results in one or more of the classic signs of Parkinson’s disease that includes resting tremor on one side of the body; generalized slowness of movement; stiffness of limbs and gait or balance problems. The cause of the disease is unknown. Both environmental and genetic causes of the disease have been postulated.
Parkinson’s disease affects about 1.2 million patients in the United States and Canada. Although 15 percent of patients are diagnosed before age 50, it is generally considered a disease that targets older adults, affecting one of every 100 persons over the age of 60. This disease appears to be slightly more common in men than women.
(Source: rush.edu)
Testosterone could combat dementia in women
In a new study, post-menopausal women on testosterone therapy showed a significant improvement in verbal learning and memory, offering a promising avenue for research into memory and ageing.
Led by Director of the Women’s Health Research Program at Monash University, Professor Susan Davis, and presented at ENDO 2103, the research is the first large, randomised, placebo-controlled investigation into the effects of testosterone on cognitive function in postmenopausal women.
Testosterone has been implicated as being important for brain function in men and these results indicate that it has a role in optimising learning and memory in women.
Dementia, which was estimated to affect more than 35 million people worldwide in 2010, is more common in women than men. There are no effective treatments to prevent memory decline.
In the study, 96 postmenopausal women recruited from the community were randomly allocated to receive a testosterone gel or a visually identical placebo gel to be applied to the skin. Participants underwent a comprehensive series of cognitive tests at the beginning of the study and 26 weeks later.
All women performed in the normal range for their age at the beginning of the trial. There was a statistically significant and clinically meaningful improvement in verbal learning and memory amongst the women using the testosterone gel after 26 weeks.
Professor Davis said the results indicated that testosterone played an important role in women’s health.
"Much of the research on testosterone in women to date has focused on sexual function. But testosterone has widespread effects in women, including, it appears, significant favourable effects on verbal learning and memory," Professor Davis said.
"Our findings provide compelling evidence for the conduct of larger clinical studies to further investigate the role of testosterone in cognitive function in women.
Androgen levels did increase in the cohort on testosterone therapy, but on average, remained in the normal female range. No negative side-effects of the therapy were observed.
Males’ superior spatial ability likely is not an evolutionary adaptation
Males and females differ in a lot of traits (besides the obvious ones) and some evolutionary psychologists have proposed hypotheses to explain why. Some argue, for example, that males’ slight, but significant, superiority in spatial navigation over females – a phenomenon demonstrated repeatedly in many species, including humans – is probably “adaptive,” meaning that over the course of evolutionary history the trait gave males an advantage that led them to have more offspring than their peers.
A new analysis published in The Quarterly Review of Biology found no support for this hypothesis. The researchers, led by University of Illinois psychology professor Justin Rhodes, looked at 35 studies that included data about the territorial ranges and spatial abilities of 11 species of animals: cuttlefish, deer mice, horses, humans, laboratory mice, meadow voles, pine voles, prairie voles, rats, rhesus macaques and talastuco-tucos (a type of burrowing rodent). Rhodes and his colleagues found that in eight out of 11 species, males demonstrated moderately superior spatial skills to their female counterparts, regardless of the size of their territories or the extent to which males ranged farther than females of the same species.
The findings lend support to an often-overlooked hypothesis, Rhodes said. The average superiority of males over females in spatial navigation may just be a “side effect” of testosterone, he said. (Previous studies have shown that women who take testosterone tend to see an improvement in their spatial navigation skills, he said.)
The analysis adds a new dimension to an ongoing debate about the evolutionary significance of some baffling human traits. Rhodes and his colleagues object to “creation stories” that seek to explain sexual phenomena like the female orgasm, rape or menopause by hypothesizing that they evolved because they provided an evolutionary advantage. Some evolutionary psychologists describe rape, for example, as an alternate mating strategy for males who otherwise are reproductively unsuccessful. Others say menopause evolved in women to enhance the survival of their genes by increasing the time spent nurturing their grandchildren. Some of these hypotheses seem intuitive, Rhodes said. “But these stories generally are not testable.”
Researchers tend to overlook the fact that many physical and behavioral traits arise as a consequence of random events, or are simply side effects of other changes that offer real evolutionary advantages, he said.
“For example, women have nipples because it’s an adaptation; it promotes the survival of their offspring,” Rhodes said. “Men get it because it doesn’t harm them. So if we see something that’s advantageous for one sex, the other sex will get it because it’s inheriting the same genes – unless it’s bad for that sex.”
Similarly, scientists who claim that the different spatial skills in men and women are adaptive must explain why women failed to inherit the superior spatial skills of their navigationally enhanced fathers, Rhodes said.
“The only way you will get a sex difference (in an adaptive trait) is where a trait is good for one sex and bad for the other,” he said. “But how is navigation bad for women? This is a flaw in the logic.”
“When people hear arguments made or stories told, particularly about human behaviors being products of adaptation, I think they should ask the question: ‘Where is the evidence?’ ” Rhodes said.
Androgenic hormones could help treat multiple sclerosis
Testosterone and its derivatives could constitute an efficient treatment against myelin diseases such as multiple sclerosis, reveals a study by researchers from the Laboratoire d’Imagerie et de Neurosciences Cognitives (CNRS/Université de Strasbourg), in collaboration in particular with the “Neuroprotection et Neurorégénération: Molécules Neuroactives de Petite Taille” unit (Inserm/Université Paris-Sud). Myelin composes the sheaths that protect the nerve fibers and allow the speed of nerve impulses to be increased. A deficit in the production of myelin or its destruction cause serious illnesses for which there is no curative treatment. The researchers have shown that in mice brains whose nerve fibers have been demyelinated, testosterone and a synthetic analog induce the regeneration of oligodendrocytes, the cells responsible for myelination, and that they stimulate remyelination. This work is published on January in the journal Brain.
(Source)
Testosterone regulates solo song of tropical birds
Experiment in females uncovers male hormonal mechanism
In male songbirds of the temperate zone, the concentration of sex hormones is rising in spring, which leads to an increase in song activity during the breeding season. In the tropics, there has been little evidence so far about such a clear relationship between hormonal action and behaviour, which is partly due to a lower degree of seasonal changes of the environment. Researchers of the Max Planck Institute for Ornithology in Seewiesen have now discovered that in duetting African white-browed sparrow weavers, the solo song of dominant males is linked to elevated levels of testosterone. What is more, the male-typical solo song could be activated via testosterone treatment in female birds. The study thus shows a complex relationship between song behaviour and hormone concentration also in a tropical bird species.
Study sheds light on role of exercise and androgens such as testosterone on nerve damage repair
A study by researchers from Emory University and Indiana University found that the beneficial effects daily exercise can have on the regeneration of nerves also require androgens such as testosterone in both males and females. It is the first report of both androgen-dependence of exercise on nerve regeneration and of an androgenic effect of exercise in females.
"The findings will provide a basis for the development of future treatment strategies for patients suffering peripheral nerve injuries," said Dale Sengelaub, professor in the Department of Psychological and Brain Sciences at IU. "And they underscore the need to tailor those treatments differently for men and women."
The researchers discussed the study on Monday at the Neuroscience 2012 scientific meeting in New Orleans.
Injuries to peripheral nerves are common. Hundreds of thousands of Americans are victims of traumatic injuries each year, and non-traumatic injuries, such as carpal tunnel syndrome, are found in even higher numbers. The researchers previously showed that two weeks of moderate daily exercise substantially improves regeneration of cut nerves and leads to functional recovery in mice, though different types of exercise are required to produce the effect in males and females. They now report that these beneficial effects of exercise require androgens such as testosterone in both males and females.
In the study they conducted, they exercised three groups of male and female mice. Nerves of the three groups were cut and surgically repaired. Once group received the drug flutamide, which blocks the androgen receptor. A second group received a placebo treatment. The third group was unexercised. Regenerating nerve fibers in the placebo group grew to more than twice the length of those in unexercised mice in both males and females. In flutamide-treated mice, the effects of exercise were blocked completely in both sexes.
The Society of Neuroscience is promoting the study (“Enhancement of peripheral axon regeneration by exercise requires androgen receptor signaling in both male and female mice”) to media covering the conference as a “Hot Topic.”
(Source: eurekalert.org)
Testosterone increases honesty
Researchers from the University of Bonn examine the biological background of lying
Testosterone is considered THE male hormone, standing for aggression and posturing. Researchers around Prof. Dr. Armin Falk, an economist from the University of Bonn, have now been able to demonstrate that this sex hormone surprisingly also fosters social behavior. In play situations, subjects who had received testosterone clearly lied less frequently than individuals who had only received a placebo. The results have just been published in the Public Library of Science’s international online journal “PLoS ONE.”
The hormone testosterone stands for typically male attributes – it fosters the forming of the sexual characteristics, increases libido and muscle building. Women also have this sex hormone, but to a much lesser extent. “Testosterone has always been said to promote aggressive and risky behavior and posturing,” reports Prof. Dr. Bernd Weber, a neuro-scientist from the Center for Economics and Neuroscience (CENS) at the University of Bonn. More recent studies indicate, however, that this sex hormone also fosters social behavior.
(Photo: Getty Images)