Biomedical Engineering Reference
In-Depth Information
range. Third, animals in each region are scored after a certain time (Fig.
1.1c
).
Scoring should be conducted with strict categories of animals based on develop-
mental stage, marker gene expression, or any detectable characters, for example,
scoring only adult animals. Then, behavioral characteristics could be recognized
with certain data visualization (Fig.
1.1d
). Calculating index is helpful to dis-
criminate different sets of animals, and several statistical methods are used to
certify the difference between each set. We should especially be careful about
statistical test for population assay when we perform nonconventional way,
because sometimes the appropriate statistical methods for population assay are
complicated, and inappropriate statistical methods make the results distorted.
Clearly, controls are necessary for behavioral assay because behavioral responses
often vary from day to day. Both negative and positive controls should be con-
tained in experimental designs.
1.2.2
Analysis for Thermotaxis as an Example
of Population Assay
One of the prominent examples of population analysis for
C. elegans
is thermotaxis
assay. Thermotaxis is observed when we grow
C. elegans
at a constant temperature
around 16-25 °C with plenty of food and put them on the plate with thermal gradi-
ent without food. The behavioral responses to the environmental temperature were
originally found and defi ned as thermotaxis in 1975 (Hedgecock and Russell
1975
);
it has been considered as one of the good model systems to elucidate behavioral
regulation by neural networks because of its simple neural network to drive the
thermotaxis (Mori and Ohshima
1995
) and powerful genetic methods of
C. elegans
(Mori
1999
). Population analysis is used for examining genetic, conditional, and
pharmacological effects (Ito et al.
2006
; Jurado et al.
2010
; Nishida et al.
2011
;
Ohnishi et al.
2011
; Sugi et al.
2011
). In a typical thermotaxis assay, animals condi-
tioned with constant temperature are placed on a thermal gradient, and the animals
show various behaviors depending on conditioning, mutation, thermal environment,
and other factors (Fig.
1.1d
).
1.3
Single Animal Analysis
Population analysis is not fi t to observe particular types of animal behavior.
For instance, a study of touch response for animals requires observation of immedi-
ate action against touch stimulus. To quantify such behavioral responses, single
animal observation works well. It is usually performed with stereomicroscope after
the isolation of single animal, but a trail on agar plate could be also used to identify
typical behavior without microscopes (Fig.
1.2a
).
