Marijuana Wreaks Havoc on Brain's Memory Cells

Marijuana wreaks havoc on brain's memory cells

* 11:38 20 November 2006 * NewScientist.com news service

* Roxanne Khamsi

Smoking marijuana often causes temporary problems with memory and learning. Now researchers think they know why.

The active ingredient in the drug, tetrahydrocannabinoid (THC), disrupts the way nerves fire in the brain’s memory centre, a new study shows.

David Robbe at Rutgers University in New Jersey, US, and colleagues gave rats an injected dose of THC, proportional to the amount inhaled by a person smoking an average-sized marijuana joint.

The team monitored the drug’s effect using wire probes placed in a memory centre in the animals’ brains – the hippocampus. The probes monitored the nerve impulses as they fired.

Normally, cells in hippocampus fire in sync, creating a current with a total voltage of around 1 millivolt. But THC reduced the synchrony of the firing. The drug did not change the total number of firings produced, just their tendency to occur at the same time – and this reduced the combined output voltage of the nerve signals by about 50%.

Abnormal firing occurs because THC binds to a receptor on the surface of the nerve cell, and so indirectly blocks the flow of current, Robbe believes.

Encore!

Nerves need to signal in sync to send a powerful message within the brain, Robbe notes. He likens the process to an audience clapping together – rather than randomly – to make their desire for an encore performance known.

Rats that had more synchronous nerve signalling in their brains performed better on a memory test, the team found. In this test, the animals had to choose whether to turn right or left in a T-shaped maze. In order to receive a treat, they had to turn in the direction opposite to the one they chose in their previous run.

Normal rats accurately alternate their routes about 90% of the time. But rats given THC, which caused asynchronous nerve firing, chose a random direction on each run, and so chose the correct route 50% of the time.

The disruptive effect of THC wore off within a few hours. Robbe says he hopes to find out whether chronic exposure to the drug causes lasting effects on the hippocampus in rats. Scientists studying people have found that long-term marijuana users gradually become worse at learning and remembering things (see Pot-smoking your way to memory loss).

Previous experiments have shown that THC can disrupt the signalling of nerve cells in a Petri dish. But Robbe says this is the first detailed account of what happens to memory cells in a live animal. He adds that the new findings help explain why people high on marijuana sometime lose their train of thought in mid-sentence, forgetting what they were saying. Journal reference: Nature Neuroscience (DOI: 10.1038/nn1801)

Gestures say so much, whatever your language

* 12:19 20 November 2006 * NewScientist.com news service

* Matt Kaplan

Language lives as much in our gestures as in our words, a new study shows.

Certain languages are richer in gesture, and such unspoken communication is so strong that bilingual individuals often use the fluent gestures from one language, even when speaking the words of another.

Simone Pika at the University of Alberta, Canada, and colleagues took a bilingual group who spoke gesture-rich languages like French and Spanish as their mother tongue, and English – a gesture-poor language – as their second language. As a control, the team also gathered a group of English-only speakers.

Each person was given a Pink Panther cartoon to describe in each of the languages they spoke. The results were clear: the bilingual individuals gestured more frequently when discussing the cartoon, even when speaking in English, Pika says.

Gesture vocabulary

More surprising was the discovery, with another group, that bilingual people with English as their mother tongue and French or Spanish as their second language also gestured far more frequently in English than English monolinguals did.

This suggests that once an enhanced gesture "vocabulary" is learned, it becomes an important aspect of communication, used alongside all languages known by the speaker.

“Language acquisition is an embodied experience and consists of visual and auditory parts,” Pika explains.

The team is now studying bilinguals with two gesture-poor languages – such as English and Japanese – to see whether simply becoming bilingual increases gesture rates.

Journal reference: Bilingualism (DOI: 10.1017/S1366728906002665)

Hard-working chips may reveal encryption keys

* 15:35 20 November 2006 * NewScientist.com news service

* Will Knight

Details of a possible weakness in the way modern microchips process cryptographic information have been published by an international team of researchers.

The flaw could let a hacker steal the cryptographic keys used to protect sensitive communications and financial transactions, simply by monitoring the amount of effort the microchip is expending, the researchers claim.

Jean-Pierre Seifert, who is affiliated with the University of Haifa, Israel, and the University of Innsbruck, Austria, and colleagues posted their findings online on Saturday.

The team say the problem is the result of a trick employed by modern microchips to speed up information processing, called "branch prediction". This involves second-guessing whether the logical flow of a computer program will follow one branch or another, prior to its actual execution.

Spy software

Branch prediction lets a modern microprocessor perform the same type of function again and again very rapidly. However, if a chip suddenly needs to perform another type of operation, or makes a mistaken branch prediction, the amount of work it has to perform, and the time required, will suddenly increase.

Understanding this effect and monitoring these fluctuations over time can reveal crucial details about encryption keys being processed, the researchers say. Although similar techniques have been proposed in the past, they have involved monitoring a chip for much longer periods.

The researcher claim to have used the attack method, dubbed "Simple Branch Prediction Analysis", to work out a highly-security 512-bit encryption key in just a few thousandths of a second. The key is of a type widely used to secure both online financial transactions and email messages against eavesdropping.

'Horrendously complicated'

The researchers suggest that a small piece of software, hidden on a target computer, could pick up cryptographic keys covertly. "Security has been sacrificed for the benefit of performance," Seifert told French newspaper Le Monde.

Markus Kuhn, a cryptography researcher at the University of Cambridge, UK, says programmers typically try to guard against so-called "timing attacks" but notes that it can be difficult to foresee every potential problem. "Modern processors are horrendously complicated and do a lot behind the scenes," he told New Scientist.

Although Simple Branch Prediction Analysis requires spy software to be installed on a target computer, Kuhn says this would be relatively simple if the computer system is open to more than one user. "If it's a multi-user machine, then it's quite a feasible threat," he says.

Seifert will present details of the attack at the RSA Security conference, in February 2007.

Edible cotton breakthrough may help feed the world

* 17:30 20 November 2006 * NewScientist.com news service

* Catherine Brahic

Cotton that has been genetically engineered so its seed is no longer toxic could provide protein-rich food for poor countries. The researchers say the technology used could make other toxic plants safe to eat.

Cottonseed contains about 22% protein, and the cotton already produced worldwide has enough protein to meet the requirements of 500 million people. But it also contains the toxin gossypol, making it poisonous to animals, including humans.

In people, gossypol lowers blood potassium to dangerous levels, resulting in fatigue and even paralysis. A surprising side effect is that gossypol is an effective male contraceptive, but research on this aspect was abandoned in the late 1990s. Attempts to eliminate gossypol from cotton plants in the 1960s and 1970s failed: insects that had previously been kept at bay by the toxin happily ate the modified plant.

Keerti Rathore of Texas A & M University in the US has managed to remove gossypol from cotton seed without affecting the toxin load in the rest of the plant, meaning the plant will contain edible seed but not be destroyed by crop pests.

Reversed sequence

Rathore and his colleagues achieved this – after what he says has been a 10-year race with teams in China and Australia – using RNA interference (RNAi) technology.

The team chose to target an enzyme that is critical in the production of gossypol. They constructed a genetic sequence that would only be active in cotton seeds and which contained a portion of the enzyme’s gene, followed by the same sequence in reverse.

They introduced their construct into cottonseed cells. There, it generated a strand of messenger RNA with two halves which stuck to each-other in a hair-pin shape.

In cells, this hairpin RNA gets chopped up into small bits by a "dicer enzyme" and, through a mechanism that is not completely understood, the small bits stick to the original enzyme’s messenger RNA. This tags the RNA, labelling it for destruction by a cellular mechanism known as the RISC complex. The net result is that the production of gossypol in the modified cottonseeds is interrupted.

Roast and grind

Rathore says the kernel of the non-toxic cotton seed can be roasted and salted and has a "nutty flavour”. He says the kernel can also been ground into a flour and combined with wheat and corn flours to enrich them with protein.

Danny Llewellyn, a plant biologist at CSIRO in Australia who has also been trying to remove gossypol from cottonseed, says the research will “allow cottonseed to be used more widely as an animal feed…and extend its uses as a substitute for other high-value oils, like canola (rapeseed) oil.”

Already, unmodified cottonseed is used in limited amounts to feed cattle, because bacteria in their rumen detoxify it. But the modified seed could make cotton plants more valuable to farmers because they could sell the seed as feed for pigs and chickens, or even human food, once they have sold the fibres around the seeds.

“It will certainly be a useful addition to cotton farmers in developing countries who grow cotton as a cash crop,” says Llewellyn. China and India are the world’s first and third largest cotton producers, respectively.

However, many developing countries have long resisted the introduction of genetically modified crops and cotton farming has been criticised for the large amounts of irrigation water it requires.

Indian pea

“RNAi technology is probably the most exciting technology of modern times,” says Rathore. “Many scientists are trying to use it to address the problems of cancer, AIDS and heart disease, but the fact is that the same technology can be used to fight food shortages too.”

He says it could be used to make another crop safe to eat, such as Lathyrus sativus, also knows as grass pea, chickling vetch, or Indian pea. This legume is an emergency crop which farmers in Asia and Africa plant in times of drought because it is resists the toughest growing conditions.

L. sativus produces a high-protein seed, but also contains a neurotoxin which paralyses the lower body when eaten in large quantities. “A lot of times when you see people with this sort of paralysis in Asia it’s because they are forced to plant grass pea,” says Rathore. He says RNAi is "perfect" to address the problem.

While Rathore's team has created gossypol-free cottonseed in the laboratory, the research remains in its early stages. The trait has been shown to be stable in three generations of plants, but the team must demonstrate it is stable in field trials, and there will be a whole series of safety tests. He does not expect his gossypol-free cottonseed to be on sale for at least 10 years.

Vital Signs

Testing: Potassium Level Is a Clue to Eating Habits

By ERIC NAGOURNEY

The day may come when skirting a doctor’s questions about your eating habits will no longer be an option. Researchers have found that a simple urine test can provide a good snapshot of how well people are really eating.

The key, they say, is how much potassium is in the urine. When the level is too low, that is the sign of a poor diet, they reported at a recent American Society of Nephrology conference.

The lead author of the study, Dr. Andrew Mente of the Prosserman Center for Health Research in Toronto, said that while doctors frequently asked patients about their diet, it was hard to get reliable information.

For this study, the researchers asked 220 kidney stone patients to collect their urine over a 24-hour period. They also asked detailed questions about what the patients had eaten.

The higher the level of potassium in the urine, the study found, the more the patients were likely to report following a balanced diet that met federal guidelines. Those patients were also likely to be less overweight and to have lower blood pressure and a lower heart rate.

Potassium can be found in a wide variety of foods, Dr. Mente said, including bananas and rice.

Because the volunteers were all being treated for kidney stones, the researchers want to find out if the association between potassium levels in the urine and good diets holds true for healthier people.

They also want to develop a single-time test, instead of one relying on urine collected over a set period of time, that will be more useful for doctors.

Really?

The Claim: Pricking a Stroke Victim’s Fingers Can Help Delay Symptoms

By ANAHAD O’CONNOR

THE FACTS A recent, widely circulated e-mail message proposes an unusual way to help the victim of a stroke. “Help the victim sit up to prevent him from falling over,” the message states. “Then sterilize a needle and use it to prick the tip of the person’s finger. After a few minutes, the victim should regain consciousness.”

The message says that doing this somehow relieves blood pressure and eases symptoms.

Like most medical advice dispensed in the form of a chain e-mail message, it has no scientific basis. In fact, following its advice can do harm.

Forcing a stroke victim to sit up is never a good idea, because it can cause a drop in blood pressure, says Dr. Larry B. Goldstein, director of the Duke Stroke Center.

It would be better to help the person lie down.

Pricking the victim’s finger is also a bad idea, not only because it is futile, but because doing so can delay medical treatment, which is the only thing that can help.

THE BOTTOM LINE Only emergency medical treatment can help a stroke victim.

In Study, Distance Running Is Tied to Skin Cancer Risk

By NICHOLAS BAKALAR

Marathon runners may have an increased risk for skin cancer, a small study published Monday suggests, and excessive sun exposure and exercise-induced suppression of the body’s immune system may be involved.

The lead author of the report, Dr. Christina M. Ambros-Rudolph, said the pilot study had reached no conclusion about the exact increase in risk that marathoners face.

But, Dr. Ambros-Rudolph said, “Our results show that there is a difference, in particular in sun exposure and measurable consequences such as increased solar lentigines.”

Solar lentigines are “age spots” caused by long-term sun exposure.

The researchers, from the dermatology department of the Medical University of Graz in Austria, studied 210 marathon runners and a control group of 210 nonmarathoners matched for age and sex. All the subjects, runners and nonrunners, were white, a risk factor for malignant melanoma, the most aggressive form of skin cancer.

Each participant had a total body skin examination, and the scientists recorded information for all participants on eye color, skin shade, history of severe sunburn and family history of skin cancer, all known risk factors for skin malignancies.

Even though, by chance, the nonrunners had more benign moles and freckles and significantly higher sun sensitivity as determined by eye color and skin shade, the runners had more solar lentigines and more lesions suggestive of basal cell and squamous cell carcinomas, two less aggressive skin cancers. The study appears in the November issue of The Archives of Dermatology.

Sun exposure may not be the only risk factor that distance runners face. The authors write that although there is no question that regular exercise is important to good health, there is good evidence that high-intensity training and excessive exercise can lead to suppressed immune function.

“This is quite well established,” Dr. Ambros-Rudolph said. “Many alterations in immune cell function have been noted at the cellular level in marathon runners.