Posts tagged testosterone levels

Testosterone may trigger a brain chemical process linked to schizophrenia but the same sex hormone can also improve cognitive thinking skills in men with the disorder, two new studies show.

Scientists have long suspected testosterone plays an important role in schizophrenia, which affects more men than women. Men are also more likely to develop psychosis in adolescence, previous research has shown.

A new study on lab rodents by researchers from Neuroscience Research Australia analysed the impact increased testosterone had on levels of dopamine, a brain chemical linked to psychotic symptoms of schizophrenia.

The researchers found that testosterone boosted dopamine sensitivity in adolescent male rodents.

“From these rodent studies, we hypothesise that adolescent increases in circulating testosterone may be a driver of increased dopamine activity in the brains of individuals susceptible to psychosis and schizophrenia,” said senior Neuroscience Research Australia researcher and author of the study, Dr Tertia Purves-Tyson, who is presenting her work at the International Congress on Schizophrenia Research in Florida this week.

Dr Philip Mitchell, Scientia Professor and Head of the School of Psychiatry at the University of NSW, said the research was very interesting.

“The relationship between sex steroids, such as testosterone, and psychiatric disorders has long intrigued researchers. For example, we have known for many years that schizophrenia presents earlier in males than females, but the biological mechanism for this has been poorly understood,” said Dr Mitchell, who was not involved in the study.

“The rodent study by Professor Shannon Weickert from the School of Psychiatry at UNSW and NeuRA is therefore of particular interest. This study suggests an important interplay between circulating testosterone levels and the brain’s sensitivity to dopamine – a neurochemical which has been long implicated in the cause of schizophrenia,” said Dr Mitchell.

“This study suggests that it is the interplay between testosterone and dopamine which is critical. This is an important observation which may very well throw an important light on solving the puzzle of the biological causes of schizophrenia.”

Cognitive thinking

A separate study by Dr Thomas Weickert at Neuroscience Research Australia examined the role testosterone plays in the cognitive thinking skills of men with schizophrenia.

The researchers examined testosterone levels in a group of 29 chronically ill men with schizophrenia or schizoaffective disorder, and a control group of 20 healthy men and asked both groups to take a series of cognition tests.

“Circulating testosterone levels significantly predicted performance on verbal memory, processing speed, and working memory in men with schizophrenia … such that increased normal levels of testosterone were beneficial to thought processing in men with schizophrenia but circulating sex steroid levels did not appear to be related to cognitive function in healthy men,” the researchers reported.

“The results suggest that circulating sex steroids may influence thought processes in men with schizophrenia.”

Dr Melanie McDowall, a researcher at the University of Adelaide’s Robinson Institute, said the study added to a large body of evidence demonstrating a link between testosterone and schizophrenia.

“This is not surprising, given the link between testosterone and dopamine,” she said, adding that symptoms of schizophrenia predominantly began after puberty.

“However, as with most endocrine and mental illnesses, schizophrenia is multifaceted (genetic, environmental etc.), hence this may not be the be all and end.”

(Source: theconversation.com)

New findings led by Dr. Michael Lombardo, Prof. Simon Baron-Cohen and colleagues at the University of Cambridge indicate that testosterone levels early in fetal development influence later sensitivity of brain regions related to reward processing and affect an individual’s susceptibility to engage in behavior, that in extremes, are related to several neuropsychiatric conditions that asymmetrically affect one sex more than the other.

Although present at low levels in females, testosterone is one of the primary sex hormones that exerts substantial influence over the emergence of differences between males and females. In adults and adolescents, heightened testosterone has been shown to reduce fear, lower sensitivity to punishment, increase risk-tasking, and enhance attention to threat. These effects interact substantially with context to affect social behavior.

This knowledge about the effects of testosterone in adolescence and adulthood suggests that it is related to influencing the balance between approach and avoidance behavior. These same behaviors are heightened in the teenage years and also emerge in extremes in many neuropsychiatric conditions, including conduct disorder, depression, substance abuse, autism, and psychopathy.

Scientists have long known that sex differences influence many aspects of psychiatric disorders, including age of disease onset, prevalence, and susceptibility. For example, according to the World Health Organization, depression is twice as common in women than men, whereas alcohol dependence shows the reverse pattern. In addition to many other factors, sex hormone levels are likely to be important factors contributing to sex differences in psychopathology.

However, research to date has mainly focused on sex hormone levels during adolescence and adulthood, when hormone levels are heightened and built upon substantial prior developmental experience. Sex hormone levels are also heightened during critical periods of fetal brain development, but the impact of such prenatal surges in sex hormone levels on subsequent adult brain and behavioral development has received relatively little attention.

"This study is the first to directly examine whether testosterone in fetal development predicts tendencies later in life to engage in approach-related behavior (e.g., fun-seeking, impulsivity, reward responsivity) and also how it may influence later brain development that is relevant to such behaviors," said first author Lombardo.

In this study, they tested a unique cohort of boys, 8-11 years of age, whose fetal testosterone had been previously measured from amniotic fluid at 13-20 weeks gestation. The boys were scanned with functional magnetic resonance imaging technology to assess changes in brain activity while viewing pictures of negative (fear), positive (happy), neutral, or scrambled faces.

They found that increased fetal testosterone predicted more sensitivity in the brain’s reward system to positively, compared to negatively, valenced facial cues. This means that reward-related brain regions of boys with higher fetal testosterone levels respond more to positive facial emotion compared to negative facial emotion than boys who with smaller levels of fetal testosterone.

In addition, increased fetal testosterone levels predicted increased behavioral approach tendencies later in life via its influence on the brain’s reward system. Lombardo explained, “This work highlights how testosterone in fetal development acts as a programming mechanism for shaping sensitivity of the brain’s reward system later in life and for predicting later tendency to engage in approach-related behaviors. These insights may be especially relevant to a number of neuropsychiatric conditions with skewed sex ratios and which affect approach-related behavior and the brain’s reward system.”

Dr. John Krystal, Editor of Biological Psychiatry, commented, “These remarkable data provide new evidence that hormonal exposures early in life can have lasting impact on brain function and behavior.”

(Source: alphagalileo.org)