Worm Breeder's Gazette 13(5): 12 (February 1, 1995)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720.
We sought to anesthetize C. elegans on culture plates to allow examination of green fluorescent protein expression by fluorescence microscopy at high magnification using a long focal length objective. We tested carbon dioxide as an anesthetic because it is effective in several organisms. Wild-type worms held under a gentle stream of CO2 stopped moving. The response was very rapid; when a stream of CO2 was placed over the animals they stopped almost immediately. Similarly, animals recovered within a few seconds of removing the CO2. The very high tech apparatus we used consisted of a stoppered 1 liter side-arm flask containing ~15 pieces (2-3 cm diameter) of dry ice, and flexible hose attached to the side-arm. CO2 sublimation forced a gentle stream of gas through the tubing, which was held a few centimeters above the surface of the plate. We presume that the effect is due to CO2. Alternatively, nematodes might doze when subjected to a gentle breeze or in response to a slight drop in temperature. We performed several carefully controlled experiments to determine whether either of these alternate explanations was plausible. To determine whether worms arrest in response to a breeze, we applied a gentle stream of air using the house air supply. When this was held over a plate of N2, many animals initially crawled backwards, perhaps due to stimulation of mechanosensory neurons, but then resumed normal locomotion. Therefore, a gentle stream of air does not induce nematode napping. To determine whether the effect was due to lower temperature, we performed two experiments. First, we determined that heating the CO2 stream to 26¡C, which was 3¡C warmer than the standard set-up, did not abolish the effect; worms still stopped moving. Second, we determined that chilling air to 21.5¡C did not anesthetize worms. Thus a stream of cool air does not cause C. elegans slumber, but a stream of warm CO2 does. In conclusion, we find that nematodes on plates can be anesthetized by placing them continuously in a gentle stream of CO2. Anesthetizing nematodes on plates could facilitate counting animals, scoring phenotypes that are difficult to see in active worms, and viewing worms on plates by fluorescence microscopy. We hope others will find this observation useful.