2 October 2010 | NewScientist | 15

Leading cause of blindness identified

THE mechanism behind a leading cause of blindness has been discovered, and could result in new treatments for a disease that causes 50 per cent of all blindness in the western world.

Age-related macular degeneration (AMD) is caused by damage to the macula – part of the retina at the back of the eye. It is thought to be linked to alterations in the gene responsible for CFH, a protein involved in the body’s immune response.

To work out how this might cause AMD, Paul Bishop at the University of Manchester, UK, and colleagues applied normal and diseased forms of CFH to maculae obtained from donated eyes.

Abnormal CFH seemed unable to bind to the macula, probably as a result of not being able to bind to two specific carbohydrates (The Journal of Biological Chemistry, DOI: 10.1074/jbc.M110.103986).

If there is not enough functional CFH bound to the macula, the immune system does not recognise the tissue as its own and so will attack it, says Bishop. “Now that we know the mechanism, we can think about treatments, such as injecting CFH into the bloodstream.”

Take antidepressants and you’ll be a soft touchWOULD you push someone in front of a train if that would save five others? Probably not if you’re on an antidepressant that raises your serotonin levels. Increased serotonin makes us less willing to hurt or punish other people, even if it is for the “greater good”, a study has found.

To test the effect of antidepressants on moral judgements, Molly Crockett and her team at the University of Cambridge presented 24 healthy volunteers with a moral dilemma while they were under the

influence of the antidepressant citalopram – a selective serotonin reuptake inhibitor (SSRI), which increases brain serotonin levels.

The participants given citalopram were about 10 per cent less willing to inflict harm on someone in order to benefit others compared with those given a placebo.

The volunteers also played a game in which they were asked to accept or decline another player’s offer of a share of a sum of money. If they accepted the offer, each player kept their share. If they

A GOOD breeze is just what a fungus needs to spread its spores, but what if the weather doesn’t oblige? It turns out some species generate their own jets of air, increasing how far their spores travel more than 30-fold.

Marcus Roper of the University of California, Berkeley, used high-speed cameras, lasers and models to film spore ejections (left image) and calculate the precise speed and motion of each spore (right image) in the crop pathogen Sclerotinia sclerotiorum and other fungi.

His team found that the combined effect of thousands of almost

simultaneous ejections creates a small air jet. This sends the spores 10 centimetres away, compared with just 3 millimetres if each cell ejects alone (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1003577107).

The videos also showed how coordination is achieved. An external cue – possibly a drop in air pressure – triggers the ejection of pioneer spores, causing mechanical changes in the surrounding tissue that trigger more ejections. The researchers say the mechanism could be common to 8000 species of fungi.

Fungi generate their own mini wind

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refused, both players were left empty-handed. People with raised levels of serotonin were more likely to accept a stingy offer, rather than punishing the other player’s greed by refusing it (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1009396107).

Crockett points out that antidepressants are the most widely prescribed class of drugs in the US and that it is therefore important to investigate their effects on users’ social behaviour and moral judgement.

The slippery slope to obesity

REWARD pathways in the brains of overweight people become less responsive as they gain weight. This causes them to eat more to get the same pleasure from their food, which in turn reduces the reward response still further.

Eric Stice, a psychologist at the University of Texas at Austin, and colleagues used fMRI brain scans to monitor 26 obese or overweight volunteers as they sipped either a tasty milkshake or a flavourless liquid resembling saliva. They compared the effect of both drinks on brain activity in the dorsal striatum, a key part of the brain’s reward circuitry. Six months later, they retested the volunteers.

Those who had gained weight since the first test also showed reduced activity in the dorsal striatum in response to the milkshake. In contrast, no change was seen in people who had lost or maintained weight (Journal of Neuroscience, DOI: 10.1523/jneurosci.2105-10.2010).

The result suggests that overeating may push people onto a slippery slope akin to a drug addict’s craving for ever-larger doses. “People are having to eat more and more to chase the high,” says Stice. It remains to be seen whether losing weight can reverse the cycle and restore normal functioning of the reward pathway.

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