Mammals sniff out sick conspecifics

Study: Old acquaintances of the immune system respond to vomeronasal organ

Schematic sketch of a mouse head with drawn vomeronasal organ including nerve connection in the olfactory brain. Bottom: Fluorescence micrographs of the VNO in cross section (overview left, detail right). The green fluorescence comes from the excitation of a green fluorescent protein (GFP) that has been genetically engineered into the VNO nerve cells. © Ruhr-University Bochum
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So far it has been a mystery how mammals can sniff out if a conspecific is ill. A hot track in solving this problem is now being pursued by biologists. They discovered that a messenger substance of the immune system, which attracts immune cells to the site of bacterial infections, also addresses receptors of the animal's nose.

The largely unexplored so-called vomeronasal organ, which responds to pheromones, is also blamed for spontaneous dislike or sympathy and choices in mate choice. The researchers led by Professor Marc Spehr and Daniela Flügge from the Ruhr University Bochum present their study on the receptor family FPR newly discovered in the olfactory system in the current online issue of "Nature".

Vital: Information from the nose

Detecting and assessing the quality of food, remote perception of possible dangers, detection of territorial boundaries or subconscious triggering lost memories - the sense of smell conveys a wealth of important information.

Fragrance signals, which are of decisive importance for social and sexual communication between conspecifics, have a special function. Such chemical signals, often referred to as pheromones, are perceived in most mammals by a special sensory organ, the vomeronasal organ (VNO).

The VNO is a tubular sensory organ at the base of the nasal septum, lined by a few thousand neurons. The nerve cells in the VNO recognize pheromones with the help of certain proteins called vomeronasal receptors. In mice, for example, about 300 different such receptors are known, which are roughly classified into two protein families - the V1R and V2R receptors. display

Proteins lead immune cells to the site of action

The enormous power of the sense of smell also includes the ability of many mammals to draw conclusions about their state of health based on the individual body odor of a conspecific. "How the sense of smell accomplishes this task and which processes are active at the level of individual nerve cells is one of the most exciting topical issues in modern neuroscience and sensory biology, " says Spehr.

In close collaboration with the team of neurogenerist Professor Ivan Rodriguez of the University of Geneva, Spehr and Fl gge have now succeeded in identifying a new family of VNO receptor proteins and investigating their function. The proteins known as formyl peptide receptors (FPRs) have so far been regarded as special proteins of the immune system.

In inflammatory reactions due to bacterial infections, they are the ones that cause the targeted migration (chemotaxis) of certain immune cells (granulocytes) to the site of infection. The receptors of bacterial degradation products, among others by so-called formyl peptides are activated.

Bacterial degradation products are smelling

Like the known vomeronasal V1R and V2R proteins, FPRs belong to the large group of G protein-coupled receptors. Using fluorescence microscopic activity measurements, the German-Swiss research network has now succeeded not only in proving the existence of five of these receptors in mammalian organs, but also in identifying important aspects of their function there.

Fl gge and Spehr were able to show that, among other things, the same bacterial substances that trigger an immune response can also activate vomeronasal nerve cells. The binding of bacterial peptides to FPRs leads to a short-term increase in the calcium concentration in the nerve cells, a signal that then causes electrical discharges of the cell.

Since the bacterial degradation products formed in inflammatory reactions are also excreted in various body secretions, the scientists now believe that they have found an important way of allowing an individual to assess the health of an individual based on their K to evaluate odor odor.

(idw - Ruhr-University Bochum, 24.04.2009 - DLO)