Published: April 27th, 2013
A method of quantitatively evaluating the chemotactic response of Caenorhabditis elegans is described. A chemotactic index (CI) was employed as a way to precisely evaluate the response of worms to certain targets, and serve as a platform of comparison between strains and compounds of interest.
Many organisms use chemotaxis to seek out food sources, avoid noxious substances, and find mates. Caenorhabditis elegans has impressive chemotaxis behavior.
The premise behind testing the response of the worms to an odorant is to place them in an area and observe the movement evoked in response to an odorant. Even with the many available assays, optimizing worm starting location relative to both the control and test areas, while minimizing the interaction of worms with each other, while maintaining a significant sample size remains a work in progress 1-10. The method described here aims to address these issues by modifying the assay developed by Bargmann et al.1. A Petri dish is divided into four quadrants, two opposite quadrants marked "Test" and two are designated "Control". Anesthetic is placed in all test and control sites. The worms are placed in the center of the plate with a circle marked around the origin to ensure that non-motile worms will be ignored. Utilizing a four-quadrant system rather than one 2 or two 1 eliminates bias in the movement of the worms, as they are equidistant from test and control samples, regardless of which side of the origin they began. This circumvents the problem of worms being forced to travel through a cluster of other worms to respond to an odorant, which can delay worms or force them to take a more circuitous route, yielding an incorrect interpretation of their intended path. This method also shows practical advantages by having a larger sample size and allowing the researcher to run the assay unattended and score the worms once the allotted time has expired.
Ward first developed the chemotaxis assay in 1973 5, and since then it has had far reaching applications. Neurobiology is one field that has benefitted from using a variety of chemotaxis assays. Olfactory adaptation, a simple form of learning and memory, has been demonstrated in C. elegans using chemotaxis assays 6. They have also been used to show that C. elegans can develop ethanol tolerance-a result that not only demonstrates the behavioral plasticity of the worms, but that also shows that the worms can be very useful in the study of alcohol dependence in humans 3. Assays have even been developed to demonstrate....
1. Preparing/washing the Worms
Comparing wild-type (N2) C. elegans to the odr-10(ky10) mutant.
We used diacetyl, a known C. elegans chemoattractant, to compare wildtype worms to that of a mutant that lacks the receptor for diacetyl 1,12. For wildtype (N2) worms the chemotactic index was 0.100±0.066 to ethanol, and 0.839±0.031 to 0.5% diacetyl. As expected, diacetyl elicits a significant chemoattractive response from wild-type worms (P<0.003). In contrast the o.......
Chemotaxis, although controlled by a complex set of neuronal and cellular mechanisms, can be easily and objectively quantified using chemotaxis assays. To obtain the best results from the assays, certain critical steps must be taken. Firstly, staging the worms is essential in yielding consistent experimental results. Worms at different life stages behave differently 13; so mixed stage worms may skew experimental results. Secondly, ensuring all E. coli is washed off the worms is crucial, as residua.......
We thank Life Sciences and the Faculty of Arts and Science at Queen's University for funding this work. As well, we thank the Chin-Sang laboratory for providing the necessary reagents, equipment and technical support. We also thank QGEM 2011, especially Tony He for his contribution to the discussion.....
|Name of Reagent/Material
|S Basal (- cholesterol) [5.8 g NaCl; 1 M K phosphate buffer, pH 6.0; dH2O to 1 liter.] Autoclave
|0.5 M Sodium Azide
|Chemotaxis Agar [1.6% BBL-agar (Benton-Dickinson) or 2% Difco-agar. Autoclave. Add 5 mM potassium phosphate, pH 6.0; 1 mM CaCl2, 1 mM MgSO4]
|Test Compounds (eg. 0.5% diacetyl)
|0.25% Tween 20
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