Parasite that makes cat-lovers neurotic

By Roger Highfield

Cat-lovers may be more neurotic than other peo- ple as a result of a feline parasite that could ultimately also be responsible for international cultural differ- ences, according to a radical theory published today.

More than a quarter of the world's population - ranging from about seven per cent of the UK popula- tion to almost 70 per cent in Brazil - is infected with Toxoplasma -gondii, a relative of the malaria bug, which also infects rats, giving them a suicidal attrac- tion to cats.

"Some of us have a parasite in our brains that

does its best to change our personalities," writes Dr Kevin Lafferty, of the University of California at Santa Barbara in the Proceedings of the Royal Society, Biology. "In populations where this parasite is very common, mass personality modification could result in cultural change."

He suggests that attitudes to ego, money, material wealth, work and rules may be affected by the para- site. Those infected by T. gondii are prone to guilt. It has been shown that, in rats at least, this helps the parasite to complete its life-cycle. An infected rat's behaviour alters so that it becomes more active, less cautious and therefore more likely to be eaten by a cat. Dr Lafferty suggested that climate affects the per- sistence of Toxoplasma and therefore that there are cultural ramifications. The parasite's eggs live longer in humid, low-altitude regions that have infrequent

freezing and thawing.

Earlier research at Imperial College London sug- gested that the parasite may also trigger schizophrenia. It showed that anti--psychotic drugs used to treat the illness prevented changes in the behaviour of rats that were infected with the parasite.

Yum, amino acids

John Whitfield Researchers have pinpointed the receptor that al- lows us to taste proteins' building blocks. The amino- acid receptor triggers the lip-smacking umami taste

that flavor enhancers exploit. Its discovery might help

the design of new additives.

Mice's version of the receptor responds to nearly all of the 20 amino acids found in proteins, Charles Zuker of the University of California, San Diego, and colleagues have found. The human version of the re- ceptor is most sensitive to the chemical glutamate. Glutamate is one of the most common amino acids in our diets. It gives high-protein food its meaty, umami flavor. About 1.5 million tons of monosodium gluta- mate is used to make food tasty each year.

Humans' more specialized receptor need not be a disadvantage, or reflect differing diets, says Zuker. It could just be a quirk of evolution. "Food rich in amino acids probably contains all 20." The ability to taste amino acids "guides us to proteins", which themselves have no taste.

Two years ago, a different research group an- nounced the discovery of an umami receptor. Whether this is the real thing has been controversial. Mice lack- ing that receptor can still taste umami, for example, and its shape raises questions about its possible func- tion.

The new receptor comprises two molecules, T1R1 and T1R3. Related molecules sense bitter and sweet flavors: T1R3 is also part of a recently discov- ered sweet-taste receptor, in tandem with another molecule T1R2. Taste receptors are big business. The US market for artificial sweeteners exceeds $600 mil- lion each year. As well as making snacks moreish, fla- vor enhancers could make food more appetizing to the elderly, who have less sensitive taste buds, or could

help ill people suffering from loss of appetite.

Different species and individuals inhabit different taste worlds. Variation in the receptor gene between human and mouse, and between individual humans, reflects this. "I'd bet that human taste preferences - whether you have a sweet tooth or not, say - are down to nothing but differences in receptor repertoire. We are starting to translate behavior into simple genetic differences," says Zuker.

His team experimented on isolated receptor- bearing taste bud cells. Next the group hopes to work out what messages these cells send to the brain, and what the brain does with this information. "We don't know how the brain determines the final taste of an amino acid," says Zuker. "I've tasted every single amino acid. Not all of them taste umami."

Knowing the molecular lock should help us de- sign keys to fit it, he says. "We could design tastes on a computer."