Cerebral Bioluminescence Technique Used to Visualize Neuronal Function

Scientists have recently developed a new technique for the in vivo imaging of neuronal function utilizing bioluminescence, based on a green fluorescent protein- (GFP)-aequorin fusion protein. This imaging technique enables the monitoring of neuronal activity (and more particularly, calcium activity), real-time and in-vivo, in either the brain as a whole or a small group of neurons.

Participating in the development were the Cellular and Molecular Neurobiology Laboratory (CNRS; Paris, France), in collaboration with the Molecular Embryology Unit, CNRS/Institut Pasteur; (Paris, France), and the Neurobiology Laboratory for Learning, Memory and Communication, CNRS/Université Paris-Sud (Paris, France).

The innovative imaging technique utilizes 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 trace neuronal activity in neurons, or even to follow it in a network of neurons. Moreover, this little-invasive and non-toxic approach allows the recording of neuronal activity over periods of several hours. It is thereby 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 physiologic phenomena related to calcium activity. Therefore, the activation by nicotine of pedunculate bodies (an important structure for learning and olfactory memory in Drosophila) induces a secondary response that is delayed by approximately 10 to 15 minutes at the level of neuronal axonal projections. It is, therefore, likely that this new response (up till now completely unsuspected) intervenes in learning and memory phenomena. Furthermore, using this imaging technique, it has been possible to track neurons in the ellipsoid body, a structure involved in regulating locomotor activity.

This innovative technique provides many perspectives. This tracer can be expressed in all cells of the brain nervous system (both neurons and glial cells) to monitor the activity of the whole brain. Preliminary data are already available. For the first time, it is possible to collect anatomic and functional maps of the brain (in this instance, of the Drosophila) based on long-term recordings. Such maps do not yet exist for any animal species, including man.

The Drosophila fruit fly is an excellent model for the study of ageing and longevity, because it has recently been shown that flies endowed with a mutation of the insulin receptor live much longer.


Related Links:
Cellular and Molecular Neurobiology Laboratory
Institut Pasteur