Thermal Stimulation Of Single Neurological Cells

Transient receptor potential channels are ion channels (holes that allow ions to transfer through cell membranes) that are found in most animals. These channels are incredibly important for the senses as chemicals representing pain, heat, pressure and taste often need to pass through them. Some of the channels are instead actually activated by chemicals themselves, such as allacin (found in garlic), capsaicin (found in pepper), methanol, peppermint or tetrahydrocannabinol (psychoactive component of cannabis).

Now optogenetics is the use of light to stimulate specific neuron sets with incredible precision. Although it can be used to study the brain and peripheral nervous system there are some serious limitations that come with the optogenetic method. For instance the ion channels being studied only react to visible light and although research is being done on the use of more penetrating infrared light, it still ha quite a bit to go and the visible spectrum is still almost exclusively used. This means that our unfortunate rodent subjects require optical fibres to be implanted in their skull for the proper stimulation of their neurons which can in turn lead to unwanted side effects associated with blindness and seizures.

The new option being investigated is thermogenetics which, as its name suggests, will use heat to activate the transient receptor potential channels rather than light. It has been possible to induce this heat using infrared radiation or positioned magnetic nanoparticles in an alternating magnetic field. Studies on fruit flies, zebrafish and mice have all shown effective results from a thermogenetic approach. As snake species are very sensitive to heat, with a thermal detection organ called a “pit” which is used to root out hiding prey, recently the receptor channels from these snake organs were used to activate the neurons of zebrafish and mice. The integrated rattlesnake channels were activated using infrared laser heating. As the laser was targeted with an incredibly precise fibreoptic probe, the heating resolution was down to the individual cell level. With incredible care, only gentle heating was required to activate the channels, minimising surrounding cell damage.

Paper links: Thermogenetic neurostimulation with single-cell resolution


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