Female brain super sensitive to stress

Researchers studied the brains of male and female rats, focusing on two regions known to play a role in learning and stress: the amygdala and the prefrontal cortex.

The amygdala, a small almond-shaped structure located deep within the brain, senses stressful situations. The prefrontal cortex, in the front of the brain, is necessary for higher cognitive functions.

“These two structures are intimately connected to one another,” says Tracey Shors, a professor of psychology at Rutgers, who is lead author of the study reported in the Journal of Neuroscience. “Therefore, we examined whether they communicate with one another to influence learning after stress.”

The researchers exposed male and female rats to stress, and then presented them with an associative learning task. During training, the rats learned to associate one event with another that occurred later in time. They played a tone and later stimulated the rats’ eyelids to elicit a blink.

After the stimulus was taken away, most of the male rats responded to the tone by blinking on their own. Most of the females, however, did not blink in response to the tone, indicating that they had failed to learn that association. But the research also contained a neurological surprise.

When Shors and her colleagues disrupted the connections between the prefrontal cortex and the amygdala in some of the females, those females were able to learn the association.

“This wasn’t true for males,” says Shors. “So, males and females are using different brain structures to learn after stress. In other words, females can learn after stress if the prefrontal cortex can’t ‘talk’ to the amygdala.

From this, we conclude that males and females can use different brain circuits to learn after stressful life events.”

Shors says sex differences in the brain may explain why women are so sensitive to stress, and why they are more likely to suffer from stress-related diseases such as depression and post-traumatic stress disorder (PTSD).

“Given these data, maybe we should consider these gender differences when we design treatments for such disorders,” Shors adds.

More from Tracey Shors at Scientific American

Increasing BPA levels in urine associated with worsening male sexual function

Increasing BPA levels in urine associated with worsening male sexual function

Increasing Bisphenol-A levels in urine are associated with worsening male sexual function, according to a Kaiser Permanente study appearing online in the Journal of Andrology.

Increasing urine BPA level is associated with decreased sexual desire, more difficulty having an erection, lower ejaculation strength and lower level of overall satisfaction with sex life, researchers said. The five-year study examined 427 workers in factories in China, comparing workers in BPA manufacturing facilities with a control group of workers in factories where no BPA was present.

BPA is an ingredient in manufacturing polycarbonate plastic and epoxy resins and is now contained in a wide variety of consumer products from baby bottles, plastic containers, and the resin lining of cans for food and beverages, to dental sealants. People can be exposed to BPA by using BPA-containing products.

In a previous related study, Kaiser Permanente researchers measured BPA exposure based on work history and environmental BPA exposure in the workplace (http://xnet.kp.org/newscenter/pressreleases/nat/2009/111109bpa.html). This new study measured urine BPA among participants and examined the correlation between their urine BPA level and their reported problems of sexual dysfunction.

"This is the first human study to show that high urine BPA is associated with lower male sexual function," said study lead author De-Kun Li, MD, PhD, a reproductive and perinatal epidemiologist at Kaiser Permanente's Division of Research in Oakland, Calif. "Also, even among men exposed to BPA from only environmental sources (no occupational exposure and with average BPA level lower than the average observed in the American population), there were indications of an increased risk of sexual dysfunction."

He explained that although the estimates in the environmentally exposed group were not statistically significant due to small sample size, this finding may enhance the understanding of the BPA effect in human populations with low-dose environmental exposure and have important public health implications.

The researchers observed a dose-response association between increasing urine BPA level and declining male sexual function. The observed negative association was consistent across all categories measuring male sexual dysfunction.

This study is the second part of Kaiser Permanente's ongoing research to look at BPA's reproductive effect in humans. Both studies are the first to look at BPA's reproductive effect in humans. The adverse effect of BPA on the male reproductive system previously had been examined in animal studies only.

Male Zebra Butterfly is pupae-sniffing cradle-snatcher

Male zebra longwing butterflies sit on the pupae of females for up to 10 days before they hatch, ensuring they get first dibs at reproducing with them. But how do they know that they're sitting on a female?

It turns out that the female pupae of Heliconius charithonia emit a pheromone as they approach puberty that betrays their gender before they've hatched. This allows males to perch on them, waiting for them to hatch. As soon as the females emerge, the males fertilise them.

Catalina Estrada at the University of Texas in Austin, and colleagues, extracted the chemicals found in the cuticles of 10 pupae and volatile organic compounds released by 12 other pupae in their laboratory.

The only chemical that was unique to female pupae was the pheromone monoterpene linalool oxide. Males emitted a variant, linalool.

The researchers then painted pupae with both odours. Male butterflies rarely perched on female pupae that had been daubed in male-specific linalool. In contrast, they happily re-perched on pupae daubed in linalool oxide 65 per cent of the time. This was almost as often as they returned to untouched female pupae.

"This paper offers insights into an unusual mating behaviour in Heliconius butterflies," says Chris Jiggins, who studies the species at the University of Cambridge.

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2009.1476

IS Sex just an Illusion

The only difference between these two faces is their degree of contrast. Yet one appears female and the other male. That's because female faces tend to have more contrast between the eyes and mouth and the rest of the face than male faces.

Richard Russell, the Harvard University neuroscientist who created the illusion, has previously found that increasing the contrast in female faces makes them more attractive. Conversely, reducing contrast makes a male face easier on the eyes.

Visit the Visual Illusion of the Year (2009) Competition and see if you have won