Sex differences in the brain's serotonin system

A new thesis from he Swedish medical university Karolinska Institutet shows that the brain’s serotonin system differs between men and women. The scientists who conducted the study think that they have found one of the reasons why depression and chronic anxiety are more common in women than in men.

Serotonin is a brain neurotransmitter that is critical to the development and treatment of depression and chronic anxiety, conditions that, for reasons still unknown, are much more common in women than in men. A research group at Karolinska Institutet has now shown using a PET scanner that women and men differ in terms of the number of binding sites for serotonin in certain parts of the brain.

Their results, which are to be presented in a doctoral thesis by Hristina Jovanovic at the end of February, show that women have a greater number of the most common serotonin receptors than men. They also show that women have lower levels of the protein that transports serotonin back into the nerve cells that secrete it. It is this protein that the most common antidepressants (SSRIs) block.

“We don’t know exactly what this means, but the results can help us understand why the occurrence of depression differs between the sexes and why men and women sometimes respond differently to treatment with antidepressant drugs,” says associate professor Anna-Lena Nordström, who led the study.

The group has also shown that the serotonin system in healthy women differs from that in women with serious premenstrual mental symptoms. These results suggest that the serotonin system in such women does not respond as flexibly to the hormone swings of the menstrual cycle as that in symptom-free women.

“These findings indicate that when developing antidepressants and anti-anxiety drugs, scientists should evaluate their effect on men and women separately, as well as their effects before and after menopause,” says Ms Nordström.

New findings contradict a prevailing belief about the inner ear

A healthy ear emits soft sounds in response to the sounds that travel in. Detectable with sensitive microphones, these otoacoustic emissions help doctors test newborns� hearing. A deaf ear doesn�t produce these echoes.

New research involving the University of Michigan and Oregon Health and Science University shows that, contrary to the current scientific thought, the emissions don�t leave the ear the same way they entered. The findings give new insight into a phenomenon that researchers study to better understand hearing loss, and they reinforce a previous controversial study that came to a similar conclusion.

A paper on the research is published in the current issue of Proceedings of the National Academy of Sciences.

�The former wisdom on how otoacoustic emissions left the ear was that there was a backward-traveling wave going along the structure of the cochlea in the same way as the forward-traveling sound wave,� said Karl Grosh, a professor in the U-M departments of Mechanical Engineering and Biomedical Engineering and an author of the paper. �These measurements show that is not the case.�

Grosh said the next step is to develop tools to find out where hearing damage is occurring. �If we want to try to infer from the emission what�s wrong with the ear, we have to understand how the emission is produced,� Grosh said.

The experiment, performed at the Oregon Health and Science University in associate professor Tianying Ren�s lab, showed that the sound waves coming out travel through the fluid of the inner ear, rather than rippling along the basilar membrane of the cochlea.

The cochlea, located deep in the ear, is shaped like a snail. The basilar membrane essentially cuts the inner channel of the cochlea diametrically in half into two chambers. Both chambers are filled with liquid.

Sound waves going into the ear undulate along the basilar membrane through the cochlea and eventually excite the organ of Corti, which senses and sends the sound signals to the brain through the auditory nerve.

Sounds coming out of the ear, according to results from this experiment, likely travel through the fluid on either side of the basilar membrane.

For this experiment, the researchers used laser interferometers, which detect waves, to measure vibrations of the basilar membrane in response to sound at two locations in the cochlea of gerbils. They detected evidence of sound waves traveling forward on the membrane, but they found no evidence of backward-traveling waves.

�Our new method can detect vibrations of less than a picometer, 1,000 times smaller than the diameter of an atom. The new data demonstrate that there is no detectable backward-traveling wave at physiological sound levels across a wide frequency range,� said Ren, principal investigator of this project. �This knowledge will change scientists� fundamental thinking on how waves propagate inside the cochlea, or how the cochlea processes sounds.�

MIT reveals superconducting surprise

MIT physicists have taken a step toward understanding the puzzling nature of high-temperature superconductors, materials that conduct electricity with no resistance at temperatures well above absolute zero.

If superconductors could be made to work at temperatures as high as room temperature, they could have potentially limitless applications. But first, scientists need to learn much more about how such materials work.

Using a new method, the MIT team made a surprising discovery that may overturn theories about the state of matter in which superconducting materials exist just before they start to superconduct. The findings are reported in the February issue of Nature Physics.

Understanding high-temperature superconductors is one of the biggest challenges in physics today, according to Eric Hudson, MIT assistant professor of physics and senior author of the paper.

Most superconductors only superconduct at temperatures near absolute zero, but about 20 years ago, it was discovered that some ceramics can superconduct at higher temperatures (but usually still below 100 Kelvin, or -173 Celsius).

Such high-temperature superconductors are now beginning to be used for many applications, including cell-phone base stations and a demo magnetic-levitation train. But their potential applications could be much broader.

“If you could make superconductors work at room temperature, then the applications are endless,” said Hudson.

Superconductors are superior to ordinary metal conductors such as copper because current doesn't lose energy as wasteful heat as it flows through them, thus allowing larger current densities. Once a current is set in motion in a closed loop of superconducting material, it will flow forever.

In the Nature Physics study, the MIT researchers looked at a state of matter that superconductors inhabit just above the temperature at which they start to superconduct.

When a material is in a superconducting state, all electrons are at the same energy level. The range of surrounding, unavailable electron energy levels is called the superconducting gap. It is a critical component of superconduction, because it prevents electrons from scattering, thus eliminating resistance and allowing the unimpeded flow of current.

Just above the transition temperature when a material starts to superconduct, it exists in a state called the pseudogap. This state of matter is not at all well understood, said Hudson.

The researchers decided to investigate the nature of the pseudogap state by studying the properties of electron states that were believed to be defined by the characteristics of superconductors: the states surrounding impurities in the material.

It had already been shown that natural impurities in a superconducting material, such as a missing or replaced atom, allow electrons to reach energy levels that are normally within the superconducting gap, so they can scatter. This can be observed using scanning tunneling microscopy (STM).

The new MIT study shows that scattering by impurities occurs when a material is in the pseudogap state as well as the superconducting state. That finding challenges the theory that the pseudogap is only a precursor state to the superconductive state, and offers evidence that the two states may coexist.

This method of comparing the pseudogap and superconducting state using STM could help physicists understand why certain materials are able to superconduct at such relatively high temperatures, said Hudson.

“Trying to understand what the pseudogap state is is a major outstanding question,” he said.

Fiber-based nanotechnology in clothing could harvest energy from physical movement

Nanotechnology researchers are developing the perfect complement to the power tie: a “power shirt” able to generate electricity to power small electronic devices for soldiers in the field, hikers and others whose physical motion could be harnessed and converted to electrical energy.

The February 14 issue of the journal Nature details how pairs of textile fibers covered with zinc oxide nanowires can generate electrical current using the piezoelectric effect. Combining current flow from many fiber pairs woven into a shirt or jacket could allow the wearer’s body movement to power a range of portable electronic devices. The fibers could also be woven into curtains, tents or other structures to capture energy from wind motion, sound vibration or other mechanical energy.

“The fiber-based nanogenerator would be a simple and economical way to harvest energy from physical movement,” said Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. “If we can combine many of these fibers in double or triple layers in clothing, we could provide a flexible, foldable and wearable power source that, for example, would allow people to generate their own electrical current while walking.”

The research was sponsored by the National Science Foundation, the U.S. Department of Energy and the Emory-Georgia Tech Nanotechnology Center for Personalized and Predictive Oncology.

The microfiber-nanowire hybrid system builds on the nanowire nanogenerator that Wang’s research team announced in April 2007. That system generates current from arrays of vertically-aligned zinc oxide (ZnO) nanowires that flex beneath an electrode containing conductive platinum tips. The nanowire nanogenerator was designed to harness energy from environmental sources such as ultrasonic waves, mechanical vibrations or blood flow.

The nanogenerators developed by Wang’s research group take advantage of the unique coupled piezoelectric and semiconducting properties of zinc oxide nanostructures, which produce small electrical charges when they are flexed. After a year of development, the original nanogenerators – which are two by three millimeters square – can produce up to 800 nanoamperes and 20 millivolts.

The microfiber generators rely on the same principles, but are made from soft materials and designed to capture energy from low-frequency mechanical energy. They consist of DuPont Kevlar fibers on which zinc oxide nanowires have been grown radially and embedded in a polymer at their roots, creating what appear to be microscopic baby-bottle brushes with billions of bristles. One of the fibers in each pair is also coated with gold to serve as the electrode and to deflect the nanowire tips.

“The two fibers scrub together just like two bottle brushes with their bristles touching, and the piezoelectric-semiconductor process converts the mechanical motion into electrical energy,” Wang explained. “Many of these devices could be put together to produce higher power output.”

Wang and collaborators Xudong Wang and Yong Qin have made more than 200 of the fiber nanogenerators. Each is tested on an apparatus that uses a spring and wheel to move one fiber against the other. The fibers are rubbed together for up to 30 minutes to test their durability and power production.

So far, the researchers have measured current of about four nanoamperes and output voltage of about four millivolts from a nanogenerator that included two fibers that were each one centimeter long. With a much improved design, Wang estimates that a square meter of fabric made from the special fibers could theoretically generate as much as 80 milliwatts of power.

Fabrication of the microfiber nanogenerator begins with coating a 100-nanometer seed layer of zinc oxide onto the Kevlar using magnetron sputtering. The fibers are then immersed in a reactant solution for approximately 12 hours, which causes nanowires to grow from the seed layer at a temperature of 80 degrees Celsius. The growth produces uniform coverage of the fibers, with typical lengths of about 3.5 microns and several hundred nanometers between each fiber.

To help maintain the nanowires’ connection to the Kevlar, the researchers apply two layers of tetraethoxysilane (TEOS) to the fiber. “First we coat the fiber with the polymer, then with a zinc oxide layer,” Wang explained. “Then we grow the nanowires and re-infiltrate the fiber with the polymer. This helps to avoid scrubbing off the nanowires when the fibers rub together.”

Finally, the researchers apply a 300 nanometer layer of gold to some of the nanowire-covered Kevlar. The two different fibers are then paired up and entangled to ensure that a gold-coated fiber contacts a fiber covered only with zinc oxide nanowires. The gold fibers serve as a Shottky barrier with the zinc oxide, substituting for the platinum-tipped electrode used in the original nanogenerator.

To ensure that the current they measured was produced by the piezoelectric-semiconductor effect and not just static electricity, the researchers conducted several tests. They tried rubbing gold fibers together, and zinc oxide fibers together, neither of which produced current. They also reversed the polarity of the connections, which changed the output current and voltage.

By allowing nanowire growth to take place at temperatures as low as 80 degrees Celsius, the new fabrication technique would allow the nanostructures to be grown on virtually any shape or substrate.

As a next step, the researchers want to combine multiple fiber pairs to increase the current and voltage levels. They also plan to improve conductance of their fibers.

However, one significant challenge lies head for the power shirt – washing it. Zinc oxide is sensitive to moisture, so in real shirts or jackets, the nanowires would have to be protected from the effects of the washing machine, Wang noted.

Predicting the radiation risk to astronauts

European scientists have developed the most accurate method yet for predicting the doses of radiation that astronauts will receive aboard the orbiting European laboratory module, Columbus, attached to the ISS this week.

The new software package accurately simulates the physics of radiation particles passing through spacecraft walls and human bodies. Such techniques will be essential to use for calculating the radiation doses received by astronauts on future voyages to the Moon and Mars.

To predict accurately the radiation risk faced by astronauts, scientists and engineers must tackle three separate problems: How much radiation is hitting the space vehicle? How much of that radiation is blocked by the available shielding? What are the biological effects of the radiation on the astronauts?
This project, funded by ESA’s General Studies Programme and the Swedish National Space Board, mostly concentrates on the second of those questions. It was initiated by Christer Fuglesang of ESA's European Astronaut Corps.

During a stay onboard the ISS in December 2006, he experienced firsthand the effects of space radiation. "You see flashes when you close your eyes as a result of interactions with your eye," he says.

The frequency of these flashes depends on where the ISS is in its orbit and the level of solar activity. There was a solar storm whilst Fuglesang was in space. "That night we were told to sleep in the more shielded sections of the station," he says.

The ESA simulation is called Dose Estimation by Simulation of the International Space Station (ISS) Radiation Environment (DESIRE). "The project was designed to provide a European capability in accurately predicting radiation doses onboard Columbus," says Petteri Nieminen, ESA’s Technical Officer on the study.

The first step was to build a programme that would accurately simulate the physics of radiation passing into a spacecraft and then through a human body. To do this, Tore Ersmark of the Royal Institute of Technology (KTH), Stockholm, Sweden worked with several existing software packages. These included a software toolkit known as Geant4, which simulates the propagation of radiation particles. Geant4 has been successfully used in disciplines such as space physics, medical physics and high-energy physics, and is developed by a large international collaboration involving ESA, CERN, and many other institutes and universities.

One of the lengthiest aspects of the work was that Ersmark had to build from scratch a computer model of the International Space Station itself. The configuration and orientation of the ISS are crucial parameters in defining the amount of matter that radiation passes through.

The Columbus module, launched into space by NASA's Space Shuttle on 7 February, is the most ambitious and sophisticated contribution to human spaceflight that Europe has yet made. It is equipped with radiation monitors to test the DESIRE predictions. "We are really pleased with the results from DESIRE and look forward to comparing them to the actual measurements," says Petteri.

Inside Columbus, during quiet solar times, the radiation levels are expected to be low. "Although they are several hundred times greater than the background radiation level here in Sweden, that is still not dangerous," says Ersmark.

Beyond Columbus, the DESIRE tool can be developed into a European software package that can be used to predict the radiation risks for other manned space flight missions, both close to Earth and beyond the protection of our planet’s magnetic field.

The radiation environment close to Earth consists of three main components: Particles trapped in the Earth’s magnetic field; particles that arrive from deep space called Galactic Cosmic Rays (GCRs) and particles expelled from the Sun during solar eruptions. These components all vary with time, mainly due to the unpredictable activity of the Sun, which influences the Earth’s magnetic field. In turn, the Earth’s field determines the extent of the trapped particles and how well Earth is shielded from incoming GCRs.

Beyond Earth’s magnetic field, spacecraft and their occupants will be exposed to the full force of the GCRs and the solar eruptions. Missions to the Moon and Mars will venture into this harsher and unpredictable radiation environment for periods of many month or even years.

During the Apollo missions of the 1960s–70s, the astronauts were simply lucky not to have been in space during a major solar eruption that would have flooded their spacecraft with deadly radiation. Essentially, they took risks and got away with it. For the kind of long-duration journeys being talked about today, a far more robust system of predicting radiation doses is required.

"The main uncertainties in these calculations are our knowledge of the space radiation environment beyond the Earth’s magnetic field, and the biological response to radiation," says Ersmark.

To provide the environmental information ESA is flying a standard radiation monitor on a number of its spacecraft, including Proba-1, Integral, Rosetta, GIOVE-B, Herschel and Planck. Known as the Standard Radiation Environment Monitor (SREM), it measures high-energy radiation particles. It was developed and manufactured by Oerlikon Space in cooperation with Paul Scherrer Institute, under a development contract from ESA.

Developing the appropriate strategies and countermeasures to deal with the interplanetary radiation hazard is essential. At present it is one of the most difficult challenges to our exploration the wider solar system. Thanks to DESIRE, Europeans have taken a step towards being able to test future space vehicle designs to find those that offer the most protection.