lit image of fruit fly larva

High-speed SCAPE microscopy captured the activity of proprioceptive neurons inside a freely moving fruit-fly larvae. [Image: Wenze Li and Rebecca Vaadia / Hillman and Grueber laboratories / Columbia University’s Zuckerman Institute, USA]

Researchers from Columbia University’s Zuckerman Institute, USA, led by OSA Fellow Elizabeth Hillman and Wesley Grueber, report creating a new way of using high-speed volumetric swept, confocally aligned planar excitation (SCAPE) microscopy to capture in video, and in real-time, nerve-cell activity in live, freely moving Drosophila melanogaster (fruit fly) larvae (Curr. Biol., doi: 10.1016/j.cub.2019.01.060).

The new imaging method is a modified version of Hillman’s original SCAPE microscopy—a hybrid imaging method that combines light-sheet and confocal-scanning microscopy. The team members say that the resulting high-resolution videos have given them better idea of how neuron location and signaling patterns inform the fruit-fly larva’s brain about body position and code for specific movements. 

Broadening SCAPE’s scope

Hillman first reported her new approach to 3-D light-sheet microscopy in 2015. She and her colleagues designed the SCAPE microscope to have only one objective lens, used for both specimen illumination and detection, and only one moving part, a scanning mirror, used to move the light sheet through the specimen. The minimalist design not only reduces the cost of the microscope, but also allows for prep-free imaging of live, freely moving specimens and for incredibly fast imaging speeds—up to 500 times faster than conventional confocal or two-photon microscopy.

Hillman and Grueber’s team optimized SCAPE microscopy for high-speed 3-D imaging of nerve-cell activity in fruit-fly larvae by improving spatial resolution to allow for high-speed 3-D imaging of individual dendrites (branches off the main body of a nerve cell). They also expanded the instrument’s field-of-view to accommodate a single live, freely moving fruit-fly larva.

The researchers chose fruit-fly larvae as a model for neuron signaling because the larvae have simple nervous systems that are easy to see through their nearly translucent bodies.

Watching nerve cells fire in real-time

Using the new SCAPE microscope, the researchers recorded larva with fluorescently labeled nerve cells as they wiggled across the imaging platform. The researchers developed algorithms to sort through and package the huge amounts of data created by each imaging session into color videos of individual nerve-cell activity within the larva’s body. 

The team captured video of individual nerve-cell activity within a squirming fly larva. [Video credit: Wenze Li and Rebecca Vaadia / Hillman and Grueber laboratories / Columbia University’s Zuckerman Institute, USA]

With these high-resolution—and, frankly, beautiful—SCAPE videos, Hillman and Grueber’s team found that a fruit fly larva’s proprioreceptive nerve cells have individual “jobs,” but work together to inform the brain of where its body is. These findings contradict previous hypotheses that state that proprioreceptive nerve signaling has an additive, partially redundant effect on fruit-fly larva movement and spatial positioning. The team also observed nerve-cell signaling patterns for specific larva movements, like crawling or moving the head back and forth.   

Hillman and Grueber say their team’s findings could “scale up to more complex systems” and may someday help researchers learn more about how neuron location and signaling patterns affect orientation and movement in humans.