Calcium Imaging: A Method to Visualize Neural Activity in Live C. elegans

Abstract

Source: Turek, M. et al. Agarose Microchambers for Long-term Calcium Imaging of Caenorhabditis elegans. J. Vis. Exp. (2015).

This video introduces the concepts behind calcium imaging and includes an example protocol for time-lapse imaging of worms contained in molded agarose wells.

Protocol

This protocol is an excerpt from Turek et al, Agarose Microchambers for Long-term Calcium Imaging of Caenorhabditis elegans, J. Vis. Exp. (2015).

1. Calcium Imaging

1. Use transgenic strains expressing genetically encoded calcium sensors such as HBR16 (goeIs5[pnmr-1::SL1-GCaMP3.35-SL2::unc-54-3'UTR, unc-119(+)]).
2. Use a compound microscope equipped for wide-field epifluorescence. Connect the TTL output of the EMCCD camera to the TTL input of the LED, so that each time the camera records a frame the sample will be illuminated. Use an exposure time of about 5 msec. Use EM gain in the range of 50 – 300.
3. Specify a burst movie running for 24 hr with each worm being imaged every 15 – 30 min first for 20 sec with DIC, then for 20 sec with a GFP fluorescence to record GCaMP, and then take a final image of the mKate2 signal is taken to control for expression levels. Use a frame rate of 2/sec during each burst.
4. For visual data inspection, use a false-color map to enhance the visibility of small changes in fluorescence intensity. Plot fluorescent data as ΔF/F, with F being the average baseline value of fluorescence. A detailed description of calcium data analysis can be found in the literature.

Materials

LED system	CoolLED	pE-2
Compound microscope	Nikon	TiE
EMCCD camera	Andor	iXon 897	now sold as iXon Ultra 897
Z-stage for the microscope	Prior	Nano Scan Z
X-Y stage for the microscope	Prior	Proscan III
Red light filter	Chroma	ET660/50m
35 mm Petri dish	Falcon	Falcon Disposable Petri Dishes, Sterile, Corning