Motivation behind the research
It has been established that electrical signals are the only form of transmission in neuroscience, however, it has been observed that these electrical signals are accompanied by thermal and mechanical changes. We hope to explore the origin of such non-electrical events.
A neuron, like any other cell, has an outer membrane composed of a lipid bilayer with embedded proteins. A simplified model of a neuron consists of an artificial lipid membrane that possesses interesting thermodynamic properties as it changes from a get to a liquid.These could explain the propagation of signals without the transfer of heat or matter together with the action potential in neurons. A solitary wave has been thought to occur when a tiny section of a membrane in its fluid phase is brought to the gel phase. Several experimental works on lipid monolayers have been carried out to test this bold idea.
We designed and built an experimental setup to assemble long artificial lipid bilayers under water, comparable in length to a large real neuron (0.1 m). To trigger a melting transition at one end of the membrane, we applied localized heat stimulation. At the other end, we immediately measured the arrival of any mechanical disturbance. We claim that this travelling bustle, triggered by heat, is a solitary wave or soliton.
A phase transition produced within a tiny region of a lipid membrane under water travels far away, suggesting that solitons may propagate in nerves.
This study only explores mechanical changes in artificial lipid membranes, but how fast this perturbation travels is still an open question. Furthermore, cell membranes are complex structures, so signal propagation in neurons involves many other membrane components that we want to include.
The results of our research might confirm that not only electrical signals explain the propagation of information along the nerves as it has been traditionally thought. The thermodynamics of a cell membrane may also play an important role in the nerve impulse. Future research will explore a different type of stimulus in artificial membranes and how the presence of anaesthetics can affect the propagation of solitary waves.
Research Article: Propagation of a thermo-mechanical perturbation on a lipid membrane, Soft Matter, 2017.