May 7 - Scientists in Singapore have discovered that sugar is the key component of a substance produced by injured fish to warn other fish of danger. The researchers say their findings could have implications for how fear is generated - and might possibly be controlled - in humans. Rob Muir reports.
The zebrafish is being exposed to a slow release of pure water through the hose at the top of its tank. The fish shows no reaction. But when scientists exchange the water for a sugar solution, the fish immediately becomes agitated, swimming frantically around the tank. It's a response the researchers interpret as fear, and according to Suresh Jesuthasan of Singapore's Agency for Science, Technology and Research , it's produced by a complex sugar molecule called Chondroiton Sulphate. SOUNDBITE (English) PRINCIPAL INVESTIGATOR AT A-STAR NEUROSCIENCE SURESH JESUTHASAN, SAYING: "The interesting thing about sugars is that they are highly complex molecules. It's the most complex substance in the biological world. And the interesting thing about the alarm response in fish is that each species has its own pheromone, and a sugar is one way you can provide a species-specific signal." Scientists have known for decades that when a fish is injured, it emits a substance that causes a fearful response in other fish nearby, but unitl now, it's makeup has been a mystery. When Jesuthasan and research colleague Ajay Mathura repeated the experiment using the substance taken directly from the skin of an injured fish, rather than sugar, the response was the same. SOUNDBITE (English) SENIOR RESEARCH FELLOW AT A-STAR NEUROSCIENCE AJAY MATHURA, SAYING: "What happens to the fish is that they would start darting, first trying to flee away from the location, but if there are in a confined space, they would try to go down to the bottom of the tank, away from the surface. And if the substance still persists, then they would freeze, which is the strongest response for an anti-predatorial response, because most predators are detecting motion, so in this case if the fish freezes, the predator is unable to see it." The zebrafish brain, when exposed to the chemical shows activity in then region associated with fear. Jesuthasan says the findings could lead to clues about the origins of fear in humans. (SOUNDBITE) (English) PRINCIPAL INVESTIGATOR AT A-STAR NEUROSCIENCE SURESH JESUTHASAN, SAYING: "It's very difficult to get an objective if you just ask people how they feel. The breakthrough came when people realised that instead of asking people, you could measure emotions, you could measure fear in an animal and then you don't have any subjective criteria anymore. And by studying mice, they've actually discovered these cellular basis for fear. And now, what people have gone on to find is that fish have very similar circuits to mice and humans when it comes to the generation of fear." And if a cellular response can be linked to fear in humans, it could lead to new insight into the nature of fear itself and how it might one day be controlled. Rob Muir, Reuters.