The active ingredient most commonly found in snake venoms, alpha-neurotoxin,
works by attaching itself to acetylcholine receptor molecules on the surface of
muscle cells. These receptors are designed to receive messages from nerves which
tell the muscles to contract or relax. But alpha-neurotoxin blocks the messages,
paralysing and ultimately killing the victim.

Sara Fuchs of the Immunology Department at the Weizmann Institute in Israel,
who is an expert on the physiology of the junctions between nerves and muscles,
studied the molecular structures of acetylcholine receptors and found that those
in mongooses and snakes are shaped so that it is impossible for snake venom to
attach to them. The receptors can still transfer messages from nerves to
muscles, and are unaffected by snake venom.

鈥淲e looked carefully at the receptor molecules on muscles in the mongoose and
found the structure was slightly different from receptors in mammals, like mice,
that do get killed by snakebite,鈥� Fuchs explains. 鈥淪imilar changes occur in
snakes so that snakes don鈥檛 get poisoned by their own toxins.鈥� In the lab, Fuchs
and her team also succeeded in changing the structure of mongoose receptors to
resemble those in animals which are sensitive to snake venom. 鈥淚n terms of
muscle receptors, we could convert a mongoose into a mouse.鈥�

Fuchs is now looking at other snake toxins to see if mongooses and snakes are
protected from their effects by similar mechanisms. She believes that this work,
and the neurotoxin research, could eventually lead to the production of new
anti-venom drugs that would use the active parts of mongoose or snake receptor
molecules and be more effective and safer to use than current drugs.

David Warrell at the Centre for Tropical Medicine at the University of Oxford
says Fuchs鈥檚 work is 鈥渧ery interesting, because it reveals one of probably many
mechanisms by which animals exposed to snake venom evade the specific action of
the venom. The receptors seem to have changed their structures under
evolutionary pressure.鈥� But he warns that developing new antivenom drugs would
be 鈥渇ar from straightforward鈥�.

Pitt鈥檚 team has been studying diseases of important crops in the southwest of
England, such as white rot in onions, take all in cereals, red core in
strawberries, and various root diseases of commercially grown flowers. In
laboratory tests, Pitt鈥檚 team mixed cultures of the disease organisms into soil,
added different types of compost and then grew the various crop plants.

The research was carried out in collaboration with an Exeter-based company
called Ecological Science, whose main business is making compost from green
waste. The project was prompted by reports from farmers that the compost was not
only helping crops to grow better but also seemed to suppress disease.

According to the company鈥檚 managing director, Tom Young, the results were
鈥渇ar better than we鈥檇 ever expected鈥�. For instance, they showed an 80 per cent
reduction in take all in wheat, while red core in strawberries was reduced by 90
per cent. Most impressively, club root in cabbages was eliminated
completely.

Ecological Science is now planning field trials in Egypt on a disease called
brown rot, which affects potatoes and tomatoes. Laboratory experiments on the
effectiveness of compost in controlling the disease, carried out by the Central
Science Laboratory in Harpendon produced promising results. In one case the
disease was suppressed completely. The work could not be done at Exeter because
brown rot is a notifiable disease in Britain. If the field trials in Egypt are
successful, Ecological Science hopes to work with the local developers to
produce a similar, locally made compost for brown rot control.

According to Pitt, organisms in compost act in several different ways to help
suppress the growth of disease-causing bacteria and fungi. Some organisms
actually prey on the pathogens, while others compete with them for nutrients or
make antibiotics.

John Elphinstone, a senior pathologist at the Central Science Laboratory,
says he is impressed by the Exeter studies, and hopes full-scale field trials
will yield similar results.

A NEW DRUG, called ondansetron, may eliminate the extremely unpleasant
side effects of drugs that are used to treat cancer, according to the results
of clinical trials. Often the powerful drugs used in chemotherapy cause
nausea and vomiting, side effects that may be so severe that they cause
doctors to abandon the treatment, particularly in children.

At the 15th International Cancer Conference held in Hamburg last weekend,
researchers presented the results of two highly successful trials of the
new drug. Richard Stevens of the Royal Manchester Children鈥檚 Hospital, presented
the results of a study that involved about 200 children suffering from leukaemia
and other cancers, while N. W. Marschner of the University Clinic, Gottingen,
West Germany, presented results of a study involving about 300 women with
breast cancer.

Among children given one cancer drug over a short period, ondansetron
completely controlled vomiting in 97 per cent of cases. Ondansetron was
between 65 per cent and 80 per cent effective when complex chemotherapy
was necessary over longer periods.

In the breast cancer studies, ondansetron was also very successful in
controlling vomiting. In 73 per cent of patients, vomiting was either completely
eliminated or was limited to just one or two episodes. By comparison, the
widely used anti-emetic drug, metoclopramide, achieves a similar level of
control in only 41 per cent of patients.

Ondansetron (trade name Zofran) is manufactured by the British company
Glaxo. It is one of a group of substances which block the action of the
neurotransmitter substance 5-hydroxytraptamine, or 5-HT (快猫短视频,
Science, 19 August 1989). Specifically, ondansetron blocks the class of
receptors known as 5-HT₃ receptors.

5-HT is stored in enterochromaffin cells in the gut (see Diagram). Anti-cancer
drugs cause these cells in the small intestine to release 5-HT. The chemicals
stimulate 5-HT₃ receptors on branches of the vagus nerve. The nerve relays
messages to a centre in the brain which triggers vomiting. The studies suggest
that ondansetron exerts its anti-emetic effects by blocking the action of
5-HT on the 5-HT₃ receptors on the vagal nerve endings, and also in the
brain in the so-called chemoreceptor trigger zone (CTZ) (see Diagram). Radiation
is also thought to cause 5-HT to be released in the gut.

Metoclopramide has also been shown to block 5-HT₃ receptors when used
in high concentrations. But its effects are much less specific than those
of ondansetron and it has serious side effects. Cancer patients receiving
chemotherapy or radiotherapy need to take metoclopramide in such high doses
that the drug can produce side effects similar to Parkinsonism, and another
serious condition called tardive dyskinesia.

Ondansetron shows none of these serious side effects and does not sedate
the patient. The only side effects are mild headaches and rashes in some
children. Stevens says: 鈥極ndansetron is safe, well tol erated and effective
in children receiving a wide variety of chemotherapeutic regimens. I鈥檓 particularly
impressed by its lack of side effects.鈥�

Andrew Beattie of Macquarie University in Sydney studied more than a
dozen species of ant. He was interested in discoveringwhy it is that ants
play almost no part in pollinating flowers, while bees and wasps, their
close relatives, do such an important job. Beattie found that pollen dies
when it touches an ant鈥檚 body. In every species he studied, it was secretions
from metapleural glands, at the rear of the ant鈥檚 thorax, that killed the
pollen.

Beattie found that the secretion is an antibiotic, called metapleurin,
which the ants use to prevent the fungi and bacteria from growing in their
bodies. The substance is a lipid molecule, which is quite different from
other antibiotics. Apart from protecting the ants, metapleurin has the side
effect of making pollen less viable and able to germinate, so it dies.

One exceptional species of ant, which lacks metapleural glands, turns
out to be an important pollinator. Beattie鈥檚 collaborator, Rod Peakall of
the University of Western Australia, has found that the winged male ant
of this species, Myrmecia urens, pollinates a common orchid of southern
Australia. M. urens pollinates up to half of the orchid鈥檚 flowers.

When Beattie realised that the secretions of the metapleural glands
had antibiotic properties, he took them to chemists to be analysed. He also
asked medical colleagues at Westmead Hospital in Sydney to test how effective
they were against bacteria that cause disease.

The hospital鈥檚 initial screening tests against more than 300 of these
bacteria have produced both good and bad results. Unfortunately, most of
the bacteria are unaffected by the antibiotics. The good news is that metapleurin
is highly effective against several strains of a common bacterium, Staphylococcus
aureus, that are resistant to other antibiotics. These bacteria can be a
major problem, sometimes preventing wounds from healing for many months
after surgery.

Since the initial trials of the antibiotic, Beattie has talked with
a major pharmaceuticals company in Britain. The company鈥檚 main interest
lies in the antifungal properties of metapleurin, because there are currently
very few effective drugs to treat internal fungal infections, which can
be fatal. The company challenged Beattie to show that ant antibiotics stop
human fungal infections. The results of tests at Westmead Hospital are just
emerging.

Two weeks ago, Beattie heard the news that a component of metapleurin
had proved highly effective against C. albicans. Metapleurin also worked
for the treatment of infections of the skin and internal tissues. Tests
against other fungal organisms are under way.