CNRS scientists in collaboration have developed a new technique for the in vivo imaging of neuronal function using bioluminescence, based on a GFP-aequorin fusion protein.
This imaging technique enables the monitoring of neuronal activity (and more specifically, calcium activity), real-time and in-vivo, in either a small group of neurons or in the brain as a whole.
Participating in the development were The Molecular Embryology Unit (CNRS/Institut Pasteur) in collaboration with the Cellular and Molecular Neurobiology Laboratory (CNRS) and the Neurobiology Laboratory for Learning, Memory and Communication (CNRS/University Paris-Sud).
The novel imaging technique employs a new, GFP-aequorin marker/tracer. This is a calcium-sensitive protein, which in the presence of its co-factor , coelenterazine, will emit light (a photon) when there is a change to the calcium concentration in a cell; for example, following neuronal activation. This makes it possible to follow neuronal activity in neurons, or even to trace it in a network of neurons. Furthermore, this little-invasive and non-toxic approach allows the recording of neuronal activity over periods of several hours. It is thus possible to monitor the cerebral activity of a Drosophila fruit fly for 24 or even 48 hours.
Because of these characteristics, the new tracer can demonstrate new physiological phenomena related to calcium activity. Thus the activation by nicotine of pedunculate bodies (an important structure for learning and olfactory memory in the Drosophila) induces a secondary response which is delayed by about 10 to 15 minutes at the level of neuronal axonal projections. It is therefore probable that this new response (hitherto totally unsuspected) intervenes in learning and memory phenomena.
Furthermore, using this imaging technique, it has been possible to record neurons in the ellipsoid body, a structure involved in regulating locomotor activity. This structure is deeply embedded in the centre of the brain and has never been studied physiologically because it was always inaccessible to standard, fluorescent-type markers. Such recordings of the ellipsoid body have thus demonstrated the considerable sensitivity of this novel approach, while validating access to all structures, even those located deep in the brain. It will therefore be possible to study all neurons or cerebral structures using this approach.