Localisation of TRP Channels in Mammalian Skin

English. Perception of temperature in mammals is critical for their survival, it enables them to perceive the world around them and act with an appropriate physiological or behavioural response. However, the full understanding of the thermosensory system in mammals has thus far been clouded. TRP channels are thermally sensitive and are known to associate with heat sensitive nerve fibers and keratinocytes in the skin. In my study the focus was understanding their thermotransduction in the rhinarium tissue and whether the sensitivity to radiating heat can be improved by keeping the rhinarium at lower temperatures (as observed in dogs). To solve this I attempted to localise TRPV1-4 and TRPM8, using immunohistochemistry, in the dog and bear rhinarium and compared the expression to other tissue types (belly). My results supported a bolometer like system, consisting of superficial TRP channel skin receptors (TRPV2, TRPV4 and TRPM8) and deep TRP channel skin receptors (all five channels). This would indicate that a colder nose would increase sensitivity to radiating heat whilst protecting the rhinarium from noxious heat.

English. Temperature Sensitisation: Has Nature Developed Its Own Bolometer? How mammals react to different temperatures is critical for their survival. Being able to sense temperature helps them understand their surrounding world and allows them to respond appropriately. Unfortunately, at present the understanding of the biological system that mammals use to perceive thermal stimuli is incomplete. However, the amazing discovery of ion channels, sensitive to specific temperatures and associate with both heat sensitive nerve fibers and specific skin cells, has brought us one large step closer to understanding this system. In my study the focus was on understanding how the naked nose tip (rhinarium) of animals such as dogs, bears, and lemurs are protected against extreme hot or cold temperatures. Furthermore, I studied whether the sensitivity to radiating heat can be improved by keeping the nose tip at lower temperatures. To solve this I attempted to localise some of these specific temperature sensitive ion channels which ranged in sensitivity from 8°C-52°C. I sectioned the tissue into slices and incubated them with a specific antibody that can bind to one of the specific ion channels. To visualise the location of the ion channel a second antibody was used that can bind specifically to the first antibody. What is clever about these second antibodies is they have a chemical compound attached to them that emits fluorescent light when exposed to a specific wavelength of light. I was able to visualise this using a fluorescence microscope, allowing me to locate where each ion channel was in the tissue. It’s getting hot (or cold) in here! The really interesting result from these experiments is that some ion channels sit very close to the surface of the skin and some sit further down. We hypothesised that this could increase sensitivity to radiating heat and help ensure quick reaction behaviour when exposed to harmful temperatures. It was thought that these ion channels may act like a biological version of a bolometer (Figure), which can detect radiation and has three main components. An absorber, which absorbs the radiation. In our system this would be the water film on the wet nose tip. Ion channels close to the surface of the skin react to the warming of the tissue. The second component is a thermal sink which is maintained at a constant temperature. In our system this would be deep skin cell and the temperature being monitored by ion channels deep in the tissue. The last component couples the first two components together. Incoming radiation hits the absorber raising its temperature quickly above the thermal sink temperature and the change in temperature can be measured by comparing the two, hopefully evoking a behavioural response. This hypothesis is just the beginning of the research and will have to be further confirmed with more experiments and animal behaviour studies. If this is in fact the case it would aid in not only further our knowledge of temperature sensation which is related to certain diseases, but also the training search and rescue animals. Advisor: Ronald Kroger Master´s Degree Project 45 credits, 2015 Department of Biology, Lund University Immunohistochemistry