Everyone knows how it feels to bite into a hot chili pepper or burn the roof of one's mouth with a hot drink. This activates nerve cells that relay the potential threat to the brain, which then causes the person in question to perceive pain. Over 14 years ago, researchers discovered the first receptor molecule that reacts to heat as well as to capsaicin, the active substance in chili extracts. At the time it was believed that science had come a big step closer to understanding the emergence of pain and its treatment with medicine.
The disappointment was great when it was found several years later that laboratory mice from whom the gene of this receptor had been artificially removed still perceived pain. Despite repeated attempts to explain the causes of this observation, it has remained a mystery until now. Researchers at the University of Freiburg have now deciphered basic mechanisms governing the perception of pain. Their findings, published in the current issue of the journal PLoS One, demonstrate that even simple organisms possess sensor systems with multiple safeguards for the perception of painful stimuli like heat.
"When we discovered that the roundworm C. elegans, which can be found in every shovelful of earth, has the same receptor genes as humans, we were optimistic that this model could help us to reveal the secret of the perception of pain," says Prof. Dr. Ralf Baumeister from the Laboratory for Bioinformatics and Molecular Genetics of the Faculty of Biology of his research team's experiments over the past years. This potentially life-saving mechanism is exceptionally well safeguarded even in such a simple animal as a roundworm. The roundworm only has 302 nerve cells at its disposal, but this small number is sufficient for complex behaviors and even for learning processes. Much as modern automobiles are equipped with electronic backup systems designed to take over and prevent fatal consequences for the passengers when a part fails, the study shows that the worm uses at least six of these cells as sensors to detect dangerous heat. In order to perceive pain, however, the worm needs to use more than one of them at a time.
In addition, one and the same cell can react to the painful stimulus with two different molecular mechanisms. Team members Shu Liu and Dr. Ekkehard Schulze thus had to apply a combination of microsurgical techniques and methods from microsystems engineering and genetics in order to grasp the mechanisms the worm uses to perceive dangerous levels of heat in all of their complexity. According to the researchers, the findings can now be used to discover and understand the interactions between the various mechanisms for these processes in humans. At least every tenth person in the Federal Republic of Germany suffers regularly from strong to very strong pain. Hence, the team's research on the tiny laboratory worm C. elegans is something everyone will ultimately profit from.
- Shu Liu, Ekkehard Schulze, Ralf Baumeister. Temperature- and Touch-Sensitive Neurons Couple CNG and TRPV Channel Activities to Control Heat Avoidance in Caenorhabditis elegans. PLoS ONE, 2012; 7 (3): e32360 DOI: 10.1371/journal.pone.0032360
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