The sense of smell of mice is doubly protected against damage, since the nose has an additional emergency command in addition to repair stem cells.
The sense of smell is doubly protected against damage, an American research team has discovered: The nose not only has repair stem cells that replace parts of the olfactory nerves destroyed by normal wear, but also a kind of emergency command in the background, which becomes active if severe damage the nerves occur. This rapid reaction force also consists of stem cells and remains practically completely idle, as long as the nerve cells are not in acute danger. If that changes, however, the cells awaken from their lethargy and take command in the nose, the researchers explain. The odor-sensitive area in the upper part of the nose contains not only the nerve cells necessary for the perception of smell, but also supporting and replacement cells. Close to the outer mucosa, there is also a layer of spherical stem cells that can be transformed into the different cell types of the olfactory mucosa as needed. This repair mechanism works quite efficiently, the scientists now showed in mice: even if all neurons in the nose are destroyed, the stem cells manage to replace them within just three weeks.

However, this system reaches its limits when not only the nerve cells, but all cells including the repair stem cells carry serious damage, for example after the action of a toxic gas: In this case, an additional stem cell group, which is also located below the olfactory mucosa, jumps in. These so-called HBCs are transformed into the repair stem cells in such emergencies, which in turn begin with the reconstruction of the olfactory mucosa, the scientists discovered. Since the HBCs are almost completely inactive except in emergency situations, it has not been possible to clarify their function.

The fact that there are two responsible for the repair of sensory cell stem cell variants in the same tissue, was previously unknown, explain the researchers. A good sense of smell, however, is extremely important in many animals, as their survival often depends on their ability to smell. But this sense is very vulnerable to damage: The nerve cells responsible for the smell belong to the so-called olfactory bulb, a small part of the brain directly above the nose. They are the only brain cells that have direct contact with the outside world and are constantly exposed to attacks of harmful substances.

Cheuk Leung (Johns Hopkins University, Baltimore) et al .: Nature Neuroscience, Online Pre-Release, DOI: 10.1038 / nn1882 ddp / science.de? Ilka Lehnen-Beyel advertisement

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