Naga

Scientists have discovered the receptors that allow snakes to find prey in the dark..
Protein ion channels allow snakes to 'see' in the dark.

Vipers, pythons and boas have holes on their faces called pit organs, which contain a membrane that can detect infrared radiation from warm bodies up to one metre away. At night, the pit organs allow snakes to 'see' an image of their predator or prey — as an infrared camera does — giving them a unique extra sense.

A study by US researchers, published online in Nature, has now revealed how this works at a molecular level. Nerve cells in the pit organ contain an ion channel called TRPA1 — an infrared receptor that detects infrared radiation as heat, rather than as light, thus confirming theories of pit-organ function long held by behavioural ecologists. The receptors are also found inside the heads of mammals, where TRPA1 channels, also known as wasabi receptors, detect pungent irritants from mustard plants or other sources.

The pit organ contains nerve fibres known as trigeminal ganglia. The researchers reasoned that a good way to home in on the organ's molecular heat detectors would be to compare the trigeminal ganglia with the dorsal root ganglia. The latter supply the brain with sensory input from the neck down and would be less likely to produce proteins that only pit-organs need to detect heat. The team looked at the different RNAs produced by each type of nerve — an indication of which genes are active and producing proteins. They found only one, TRPA1, which was being expressed differently in the two types of ganglia, with the gene in the trigeminal ganglia producing 400 times more RNA than that in the dorsal root ganglia.