In a recent study, researchers have discovered a novel way to monitor changes and observe ion fluxes, by examining the characteristics of water molecules surrounding the neural membranes. The research team at the Ecole Polytechnique Fédérale de Lausanne (EPFL) have tested the method on in vitro neurons of mouse and published their findings in the journal Nature Communications.
Neurons in the brain communicate with each other through the electrochemical signals transmitted along the axons. When sending a signal in the form of an electric charge, neurons enable ions to pass through its membrane using the ion channels. Transfer of these ions creates an electrical potential difference between the inside and outside of the neurons, which is known as the membrane potential.
An insight to the electrical activity of the neuron could enable a better understanding of numerous processes occurring inside the brain. Until now, the only way to monitor changes in the neuronal activity was either by attaching electrodes onto or injecting fluorophores into the region of the brain being examined. However, fluorophores are fluorescent chemical compound that can be toxic, while the electrodes may cause damage to the neurons.
Recently, the researchers at the EPFL’s Laboratory for fundamental BioPhotonics (LBP) have devised a method to track neurons’ electrical activity by evaluating the interaction between the neural membranes and water molecules. According to Sylvie Roke, LBP’s director, neurons are surrounded by water molecules which change their orientation in response to an electric charge. It was observed that the water molecules re-orient when the membrane potential changes.
In the new study, the research team altered the membrane potential of the neuron by subjecting them to rapid influx of potassium ions. Due to this, the ion channels on the surface of the neurons – which facilitate the membrane potential – opened and let the ions through. When the flow of ions was turned off, the neurons released the ions that they had accumulated.
For monitoring this activity, the researchers illuminated the neurons with two laser beams of the same frequency and examined the hydrated neuronal lipid membranes. The beams consist of femtosecond laser pulses that allowed the water molecule on the membrane interface to generate photons of different frequency called second-harmonic light.
According to the researchers, the study not only helps gain insights to mechanisms the brain employs to send information but also could appeal to pharmaceutical companies looking for in vitro product testing.