Scientists plan to develop a new range of less addictive and more effective painkillers after discovering how nicotine acts on the brain to ease pain.

At present drugs such as morphine are used to dull severe pain, but they are extremely addictive and potentially dangerous if misused.

Nicotine, the addictive element in cigarettes, dulls pain by interacting with certain receptor molecules in the brain.

Scientists have isolated and cloned 10 nicotine receptors but until now they had not known which receptors were responsible for nicotine's varied behavioural effects.

But, according to the science journal Nature, a team of scientists at the Molecular Neurobiology Unit at the Institute Pasteur in Paris have discovered two receptors - known as alpha-4 and beta-2 - that play a major role in how nicotine reacts with the brain.

Toxic effects

Nicotine itself cannot be used as a painkiller because of its addictive properties and toxic effects on the heart and lungs.

But scientists may be able to create compounds which act in a similar way to dull pain.

Researcher Lisa Marubio said: "Compounds that are similar to nicotine that can be synthesised in a lab can possibly be used as potential new analgesics that can be every bit, if not more, efficacious than morphine."

The researchers tested the reaction of normal mice and "knockout" mice bred without pain receptor genes.

Both types of mice felt pain without the nicotine, but only the ordinary mice felt less pain when they were given nicotine.

Scientists have already started looking at nicotine and nicotine-like compounds as a new class of painkiller.

Writing in Nature, the French team says: "Specific pharmacological compounds that target these receptors may prove to be therapeutically useful for analgesia."