The probe, which was developed by a team of Vanderbilt scientists, is a genetically modified form of luciferase, the enzyme that a number of other species including fireflies use to produce light.
The scientists created the technique as a new and improved method for tracking the interactions within large neural networks in the brain.
"For a long time neuroscientists relied on electrical techniques for recording the activity of neurons. These are very good at monitoring individual neurons but are limited to small numbers of neurons. The new wave is to use optical techniques to record the activity of hundreds of neurons at the same time," said Johnson, Stevenson Prof. of Biological Sciences, who headed the effort.
"Most of the efforts in optical recording use fluorescence, but this requires a strong external light source which can cause the tissue to heat up and can interfere with some biological processes, particularly those that are light sensitive," he said.
Based on their research on bioluminescence in "a scummy little organism, the green alga Chlamydomonas, that nobody cares much about" Johnson and his colleagues realized that if they could combine luminescence with optogenetics – a new biological technique that uses light to control cells, particularly neurons, in living tissue – they could create a powerful new tool for studying brain activity.
"There is an inherent conflict between fluorescent techniques and optogenetics. The light required to produce the fluorescence interferes with the light required to control the cells," said Johnson. "Luminescence, on the other hand, works in the dark!"
Johnson and his collaborators – Associate Prof. Webb, Research Assistant Prof. Shi, post-doctoral student Yang and doctoral student Cumberbatch in biological sciences and Prof. Winder and postdoctoral student Centanni in molecular physiology and biophysics – genetically modified a type of luciferase obtained from a luminescent species of shrimp so that it would light up when exposed to calcium ions. Then they hijacked a virus that infects neurons and attached it to their sensor molecule so that the sensors are inserted into the cell interior.
The researchers picked calcium ions because they are involved in neuron activation. Although calcium levels are high in the surrounding area, normally they are very low inside the neurons. However, the internal calcium level spikes briefly when a neuron receives an impulse from one of its neighbors.
MEDICA-tradefair.com; Source: Vanderbilt University