Nicotine receptors in the mouth open up possibility of new anti-smoking therapies

Scientists in Portugal and the US have found nicotine receptors in the taste buds, which could suggest a possible new target for anti-smoking drugs.

Until now it was believed that nicotine, which leads to smoking addiction, had to migrate into the brain – where its specific receptors existed – to provoke its effects.

This new discovery, published by Albino Oliveira-Maia and colleagues in the Proceedings of the National Academy of Sciences (PNAS), reveals a second recognition pathway that most probably contributes to smoking addiction. On this pathway, anti-smoking drugs can be applied on the tongue, drastically reducing their side effects.

This pathway is also shown to activate a brain area that when damaged can lead to instant loss of smoking addiction, suggesting that mouth nicotine receptors can play a key role in the dependence process.

The scientists studied a mouse lacking a protein – called TRPM5 – linked to the recognition of bitter tastes (nicotine is known to be bitter) since previous research suggested that taste is important for tobacco addiction.

When comparing normal animals against those lacking TRPM5 in the presence of nicotine and quinine solutions, it was discovered that, although incapable of tasting bitter flavours, TRPM5-negative animals could still distinguish nicotine from water and also from quinine.

Further studies in rats revealed the existence of nicotine receptors in the taste receptor cells and taste nerves of the mouth. However, when nicotinic cholinergic receptors (nAChRs) inhibitors – used to stop smoking – were put on the tongue, both the behavioural and neural effects of nicotine became similar to those obtained with quinine.

The discovery raises the possibility of using anti-smoking drugs topically and avoiding many of the side effects seen when the drugs are used sistemically, and also contributing to more efficient anti-smoking therapies.