Researchers at Howard Hughes Medical Institute have developed a method to dupe nerve cells to manufacture a protein that lights up when those cells depolarize. The fluorescent indicator, GCaMP3, for the first time allows live monitoring of large number of neurons as they undergo single action potentials. This amazing functional modality might open new possibilities in the study of neural networks.
Looking at the structure of GCaMP2, Looger could see exactly how the molecule grabbed on to calcium and turned this into brighter fluorescence. It did not take long before he and his team roughed out ideas for making modifications to the molecule that would make it grab calcium more tightly. They also identified a second set of modifications would make the molecule glow more brightly. Looger’s team made those adjustments and wound up with GCaMP3, which he says is three times brighter, three times more sensitive to calcium, and binds the calcium 1.3 times more tightly than GCaMP2.
With the new indicator in hand, Looger collaborated with Janelia Farm fellow Vivek Jayaraman to test GCaMP3’s power to track the activity of a single neuron in the fruit fly brain. “The tiny size of the fruit fly brain makes recording from its neurons with electrodes exceedingly hard,” explains Jayaraman. “GCaMP3 provides a non-invasive way to measure the activity of specific neurons with a bright signal that is unprecedented for such sensors.” Jayaraman says his research group uses the tool for their studies of the neural circuitry that guides visual processing.
GCaMP3 also proved useful in revealing neural activity in another popular animal model, the flatworm C. elegans. Cornelia Bargmann’s lab at Rockefeller genetically engineered worms that expressed the new calcium indicator in a neuron known to detect odors, and watched that neuron light up as certain smells were presented and taken away. The increase in fluorescence when the neuron fired was far more dramatic than the team saw with earlier generation GCaMPs.
Looger also collaborated with Janelia group leader Karel Svoboda to use GCaMP3 for imaging brain activity in the mouse. They engineered mice that produced GCaMP3 in a group of neurons that processes information from just one of the animal’s whiskers. They were able to watch 13 neurons within that group light up in a particular sequence as the mouse walked and the whisker moved.
Video and links are after the jump:
Press release: Teasing Apart Brain Function, Neuron by Neuron …
Abstract in Nature Methods: Imaging neural activity in worms, flies and mice with improved GCaMP calcium indicators