A New Technique Developed For Imaging Zebrafish Brain

Researchers from Cornell University have developed a new technique to image a zebrafish’s brain at all stages of its development, which could help in the study of human brain disorders, including autism.

When young, Zebrafish are translucent which makes them good models for live imaging but as they become adult they become opaque and this has prevented researchers to image the adult brain.

But this problem seems to be solved by a team from Cornell Neurotech. They have developed a microscopy tool to use with adult zebrafish engineered with calcium sensors that light up when neurons get activated.

As all the vertebrate brains are similar, studying zebrafish would enlighten us with the structure and functions of the vertebrate brain at a fundamental level.

“All vertebrate brains are, to a first approximation, the same, with nearly all brain regions present in nearly every vertebrate,” said Joseph Fetcho, professor of neurobiology and behavior and director of Cornell Neurotech in the College of Arts and Sciences. “This is not surprising because they all, even the simplest ones, have to do the same things to survive and reproduce.“

When nerve cells activate, they flood with calcium. The fish used in Fetcho’s studies are engineered with a protein that binds to the calcium in nerve cells. The protein also fluoresces when excited by laser light with a 480-nanometer wavelength, and the fluorescing cells can be imaged with a microscope.

The problem was when they delivered the pulse of light, a single 480nm photon aimed through the top of the fish’s head will excite other fluorescent proteins in the beam’s path, blurring the image.

The new technique works by delivering 1400nm wavelength photons to a focal point in the brain. This way, each individual photon has a wavelength that’s too long to excite intermediary proteins, but three photons together will carry enough energy to excite a fluorescent protein when light is concentrated at the focal point.

The laser then scans repeatedly along a line in the brain. By repeatedly imaging, parallel lines add up to a two-dimensional cross-section of a brain region. By repeating this process at different depths, the researchers attain a three-dimensional image of brain structures.

With the new tool, researchers can use fish that are engineered to develop a version of autism and brain-related disorders and watch how the disease progresses as the fish ages. These fish models could also be used to test potential treatments to see if they improve function, and how brain structure and function change if a condition improves.

“This is a step … toward cures for some of the devastating brain disorders faced by humans,” Fetcho said.

Fetcho is a co-senior author of the paper published in Nature (linked below). The other senior author is Chris Xu, professor of applied engineering and physics in the College of Engineering and the Mong Family Foundation Director of Cornell Neurotech-Engineering.

Journal
Dawnis M. Chow et al, Deep three-photon imaging of the brain in intact adult zebrafish, Nature Methods (2020): DOI: 10.1038/s41592-020-0819-7