Shedding light on the inner circuits of the brain

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Image: CaMPARI fluorescence in a larval zebrafish brain showing active neurons (magenta) that were marked while the fish was freely swimming. (Looger Lab, HHMI/Janelia)
Image: CaMPARI fluorescence in a larval zebrafish brain showing active neurons (magenta) that were marked while the fish was freely swimming. (Looger Lab, HHMI/Janelia)

Researchers in the US have developed a novel method of visualizing active parts of an animal’s brain. A team of scientists from Howard Hughes Medical Institute in Ashburn, Virginia, have created a fluorescent protein called CaMPARI (calcium-modulated photoactivatable ratiometric integrator), which lights up when activated neurons fire signals in the brains of living organisms.

“The most enabling thing about this technology may be that you don’t have to have your organism under a microscope during your experiment. So we can now visualize neural activity in fly larvae crawling on a plate or fish swimming in a dish,” said Dr Loren Looger (The Looger Lab), describing the main advantage of CaMPARI over existing technologies.

His team started with a green fluorescent protein called Eos that converts to a red fluorescent species when exposed to violet light. They attached Eos to calcium-binding proteins called calmodulins, ensuring that the green to red conversion only takes place in the presence of high calcium content (a characteristic of active neurons) and on exposure to violet light.

“Ideally, we can flip the light switch on while an animal is doing the behavior that we care about, then flip the switch off as soon as the animal stops doing the behavior. Then we’re capturing a snapshot of only the activity that occurs while the animal is doing that behavior,” said Dr. Eric Schreiter, a senior scientist in the Looger lab.

CaMPARI has been used to validate existing data from previous brain activity mapping experiments in model organisms including the fruitfly and zebrafish. Efforts are under way to extend its use to other organisms such as mice.

Watch CaMPARI in action: http://bcove.me/tbh4k1d3

The original article can be accessed here.