MICROSCOPY/NEUROLOGY/CELL BIOLOGY/DRUG DEVELOPMENT: High-resolution holographic microscopy enables 3-D live-cell imaging of neuronal activity

Observing neurons in a Petri dish traditionally involves fluorescent dyes, which change the cells’ chemical composition and thus can skew results. Besides that, the standard approach is time consuming and allows examination of only a few neurons at a time. But the results of a new study by Swiss scientists—neurobiologists, psychiatrists, and advanced imaging specialists at École Polytechnique Fédérale de Lausanne (EPLF) and Centre Hospitalier Universitaire Vaudois (CHUV)—demonstrate how DHM can overcome these limitations.1 Thanks to the precision, speed, and noninvasiveness of the approach, it can be used to track minute changes in neurons, and thus is promising for testing of drugs to control neurodegenerative diseases such as Alzheimer’s and Parkinson’s. “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,” says Pierre Magistretti of EPLF’s Brain Mind Institute.

Depicted by digital holographic microscopy, a neuron can be imaged with resolution to 10 nm.
Depicted by digital holographic microscopy, a neuron can be imaged with resolution to 10 nm.

To enable neuronal study through DHM, the research 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 can be detected only by DHM. Thus, the technique accurately visualizes the electrical activities of hundreds of neurons simultaneously, in real-time.

Normally used to detect microscopic defects in materials science, “DHM is a fundamentally novel application for studying neurons with a slew of advantages over traditional microscopes,” Magistretti explains, adding that it allows for extended observation of neural processes. According to senior team member Pierre Marquet, “DHM gives precious information not only about the shape of neurons, but also about their dynamics and activity, and the technique creates 3-D navigable images and increases the precision from 500 nm in traditional microscopes to a scale of 10 nm.”

The scientists say DHM can be applied to high content screening (HCS) for drug discovery and development. The technology has already been commercialized by the EPFL start-up LyncéeTec.

1. P. Jourdain et al., Neurosci. 31, 33, 11846–11854 (2011).

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