Reconstructing brain circuits

February 8, 2018 ZEISS Microscopy

A carbon nanotube coated tape for serial-section electron microscopy

An international research team centered at Japan’s National Institute for Physiological Sciences with German Max Planck Institute and ZEISS Microscopy developed a carbon nanotube (CNT) tape for facilitating serial-section electron microscopy used for reconstructing brain circuits. The superior properties of the described tape enable even larger-scale imaging projects – as imaging becomes more reliable and image quality is improved. In particular high-throughput imaging devices such as ZEISS MultiSEM benefit from this recent development.

What is the neural basis of our minds and consciousness?

Researchers believe the answer resides in the precise “wiring diagram” of our brains, the connections between all of its neurons. However, little is known about the details of this wiring diagram because existing methods for mapping the brain’s circuits are inadequate. Scientists from Japan’s National Institute for Physiological Sciences and their collaborators have made a substantial advance in the method for automatically collecting thin brain sections that are then used for reconstructing its wiring diagram. These wiring diagrams not only elucidate normal brain function but can also be used for the diagnosis of neurodegenerative diseases such as schizophrenia, Alzheimers and autism.

The brain consists of neurons and their connections to each other. Shown is an example of a single connection, called a synapse, between two neurons; PSD = post-synaptic density.

CNT tape enables high-resolution volume electron microscopy of brain circuits

The team started by observing short-comings in existing tapes used for collecting thin sections and set out to develop a better tape, which they did by adding carbon nanotubes to coat a conventional plastic tape, PET. They called the combination CNT-PET tape. The carbon nanotubes render the PET tape conductive, allowing the sections collected on it to be imaged with electron microscopy. Without the CNT conductive coating, the sections would charge during imaging, precluding the reconstruction of the brain’s circuits. The advance made with CNT-PET tape will greatly facilitate the collection and subsequent imaging of serial brain sections using a recently developed ATUM-SEM pipeline, which is used for brain circuit reconstruction.

(Upper panel) The new conductive tape is made by coating conventional PET tape with carbon nanotubes (CNTs) to generate CNT-PET tape. (Lower panel) Sample electron microscopy image from a brain section collected on CNT-PET tape showing good ultrastructure without any charging artefact.

Abstract: Automated tape-collecting ultramicrotomy in conjunction with scanning electron microscopy (SEM) is a powerful approach for volume electron microscopy and three-dimensional neuronal circuit analysis. Current tapes are limited by section wrinkle formation, surface scratches and sample charging during imaging. Here we show that a plasma-hydrophilized carbon nanotube (CNT)-coated polyethylene terephthalate (PET) tape effectively resolves these issues and produces SEM images of comparable quality to those from transmission electron microscopy. CNT tape can withstand multiple rounds of imaging, offer low surface resistance across the entire tape length and generate no wrinkles during the collection of ultrathin sections. When combined with an enhanced en bloc staining protocol, CNT tape-processed brain sections reveal detailed synaptic ultrastructure. In addition, CNT tape is compatible with post-embedding immunostaining for light and electron microscopy. We conclude that CNT tape can enable high-resolution volume electron microscopy for brain ultrastructure analysis.

Read the full paper:  Yoshiyuki Kubota, Jaerin Sohn, Sayuri Hatada, Meike Schurr, Jakob Straehle, Anjali Gour, Ralph Neujahr, Takafumi Miki, Shawn Mikula & Yasuo Kawaguchi, A carbon nanotube tape for serial-section electron microscopy of brain ultrastructure, Nature Communications volume 9, Article number: 437(2018)

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