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.

Making Worms Sit Still on Plates.

Wayne Forrester, Gian Garriga

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