Snot affects out sense of smell: Study

Washington, Dec 2 (ANI): A new study in mice has found out that enzymes in nasal mucus change certain scents well before the nose can detect them.

This might explain why a rose sniffed through a snotty nose may not smell so sweet.

The study results showed that lowly mucus might feature prominently in the sense of smell, reports Discovery News.

"It is completely unexpected that snot would play a potential role in changing how we perceive odours," said neuroscientist Leslie Vosshall at Rockefeller University in New York City.

But there's more to mucus than what meets the nose: The thick goo that serves to lubricate the nose is teeming with proteins and protein-chopping enzymes.

Some of these molecules are thought to catch smells and shuttle them to odour receptors in the nose. Other components may protect the body from toxic chemicals by chopping them up into harmful pieces. But no one knew whether this chopping action had any effect on smell perception.

In the new study, Ayumi Nagashima and Kazushige Touhara of the University of Tokyo added particular odorants to tiny amounts of mucus sucked out of a mouse's nose and tested the resulting chemical composition of the mix.

After five minutes of sitting in mucus, about 80 percent of almond-smelling benzaldehyde was converted into benzyl alcohol (a scent found in some teas and plants) and odourless benzoic acid.

The team found that inactive enzymes in boiled mucus could not do this odour conversion.

They reported that snot enzymes could cut up aldehydes and molecules with chemical features called acetyl groups. Scents from these kinds of molecules are common in flowers, plants and animals (and perfumes: aldehydes feature prominently in Chanel No. 5's formulation).

They found that the odour transformation happened inside the mice's noses and was reflected in their brains, too. Parts of the mouse brain called glomeruli get signals from mice's smell-sensing nerve cells.

When the researchers inactivated a scent-chopping enzyme in the mice's noses, the pattern of glomeruli activation changed, suggesting that the snot enzymes affect what the mouse smells.

Mice's behavior confirmed this altered sense of smell. Mice were trained to associate sugar with a particular odour. Later, the mice were presented with two smells, one that usually comes with a treat and one that doesn't.

Normally, the mice spent more time nosing around the smell that came with a treat. But when mucus enzymes were inactivated, the mice spent less time sniffing around the treat-linked smell, suggesting that they could no longer recognize the odour.

That the mucus enzymes could act on the odours before the nose could detect them was unexpected, said neuroscientist Sigrun Korsching of the University of Cologne in Germany, but added that the behavioural tests are convincing in that respect."

It is, however, unclear whether humans experience the same mucus effect. Some of the same mucus enzymes are also found in people, and preliminary data from other researchers suggested that nasal enzymes can change odorant quality for humans, said Touhara.

The study is published in the current issue of the Journal of Neuroscience. (ANI)