Scientists have discovered a way to observe living neurons without damaging them – in 3D and with up to 50 times greater resolution than before. The technique, using digital holographic microscopy (DHM), is non-invasive and can create imagery of hundreds of neurons at once. DHM has the potential to streamline drug studies involving neurodegenerative diseases such as Parkinson’s and Alzheimer’s, because researchers can test new drugs more quickly and in greater numbers than before.
The research team, from Switzerland’s École Polytechnique Fédérale de Lausanne (EPLF) and Centre Hospitalier Universitaire Vaudois (CHUV), included neurobiologists, psychiatrists, and advanced imaging specialists. Results of their collaboration appear in the August 17, 2011 issue of The Journal of Neuroscience.
To observe transparent neurons in a petri dish, scientists typically use fluorescent dyes. But this technique is time-consuming, often damages the cells, changes the chemical composition – potentially skewing the results – and allows researchers to examine only a few neurons at a time.
According to the new study, DHM can bypass the limitations of existing techniques. Pierre Magistretti, of EPFL’s Brain Mind Institute and a lead author of the paper, explained:
DHM is a fundamentally novel application for studying neurons with a slew of advantages over traditional microscopes. It is non-invasive, allowing for extended observation of neural processes without the need for electrodes or dyes that damage cells.
Team member Pierre Marquet added:
DHM gives precious information not only about the shape of neurons, but also about their dynamics and activity, and the technique creates 3D navigable images and increases the precision from 500 nanometers in traditional microscopes to a scale of 10 nanometers.
A good way to understand how DHM works is to imagine a large rock in an ocean of perfectly regular waves. As the waves deform around the rock and come around the other side, they carry information about the rock’s form. By comparing that information to information from waves that did not smash up against the rock, it would be possible to reconstruct an image of the rock. DHM does this with a laser beam by pointing a single wavelength at an object, collecting the distorted wave on the other side, and comparing it to a reference beam.
A computer then numerically reconstructs a 3D image of the object – in this case, neurons – using an algorithm developed by the authors. In addition, the laser beam travels through the transparent cells and obtains important information about their internal composition.
In the past, scientists used DHM for detecting defects in materials, but Magistretti and DHM pioneer Christian Depeursinge decided to use DHM for neurobiological applications. Their group provoked an electric charge in a culture of neurons using glutamate, the main neurotransmitter in the brain. This charge transfer carries water inside the neurons and changes their optical properties in a way that only DHM can detect. The result is imagery of the electrical activity of hundreds of neurons simultaneously in real-time, without damage by electrodes, which can record activity from only a few neurons at a time.
Without the need to introduce dyes or electrodes, researchers could apply DHM to high content screening – the screening of thousands of new pharmacological molecules.
Due to the technique’s precision, speed and lack of invasiveness, it is possible to track minute changes in neuron properties in relation to an applied test drug and allow for a better understanding of what is happening. What normally would take 12 hours in the lab can now be done in 15 to 30 minutes, greatly decreasing the time it takes for researchers to know if a drug is effective or not.
Bottom line: A research team from Switzerland’s École Polytechnique Fédérale de Lausanne (EPLF) and Centre Hospitalier Universitaire Vaudois (CHUV) has published a paper in the August 17, 2011 issue of The Journal of Neuroscience, detailing their application of digital holographic microscopy (DHM) to living neurons.
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