Heidelberg, Germany--Researchers at the Max Planck Institute for Medical Research are using two-photon laser-scanning microscopy to detect optical changes in neurons, giving them the ability to measure activity patterns such as mental activity and reactions to sensory stimulation.
Neurons communicate with one another via so-called action potentials. During an action potential, voltage-gated calcium channels are opened resulting in rapid calcium ion influx. Because of this tight coupling, fluorescent calcium indicator proteins can visualize action potentials. These proteins have two fluorescent subunits, one of which radiates yellow light and the other blue. When the proteins bind calcium, the proportion of yellow to blue light changes. Color variation from blue light towards yellow thus reports different calcium levels -- which is why the protein has been dubbed a "chameleon."
Measuring action potentials optically
With the chameleon protein YC3.60, a fairly new variant, the scientists succeeded in recording the reaction of nerve cells to sensory stimuli in the intact brain of mice: every time the whiskers were deflected by a puff of air, there was a change of color in the chameleon proteins in the nerve cells of the sensory areas of the cortex. It could therefore be deduced that the affected cells had reacted to the stimulus with action potentials.
The scientists were able to investigate activity in single cells as well as in whole groups of nerve cells. "YC3.60 has therefore proven to be a suitable tool for studying nerve tissue at different levels: on the one hand, we can monitor the fluctuation of calcium to infer action potentials within nerve cells. And what is even more advantageous, we can simultaneously measure the activity of neural networks or entire brain regions," says Mazahir Hasan.
Using fluorescence to study the brain provides a unique opportunity to investigate how memories are formed and lost and, furthermore, when and where nerve-cell activity patterns become altered as in the case of aging and also in neurological diseases such as Alzheimer's disease, Parkinson's disease, and schizophrenia.
--posted by John Wallace