Biomedical Engineering Reference
In-Depth Information
1.1
Introduction:
C. elegans
as a Model Organism
for Behavioral Analysis
About 1 mm long, tiny nematode
Caenorhabditis elegans
has been used for
biological research as an important model organism for nearly 40 years (Brenner
1974
). An abundant advantage for scientifi c studies such as short life cycle, trans-
parent body, and convenience of genetic analysis has been pushing various fi elds of
research including genomics, cell biology, development, aging, and neuroscience.
Since behavior is an eventual output of biological system, accumulated detailed
knowledge about
C. elegans
tremendously contributes to uncover the mechanisms
of behavioral regulation. Complete anatomical dissection exhibited connectivity
and identity of all 302 neurons for an adult hermaphrodite and 383 neurons for adult
male; furthermore, we can easily search such anatomical map by using online data-
base (Hunt-newbury et al.
2007
). Together with genetic database that provides
genome information (Harris et al.
2010
), abundant information at cellular, molecu-
lar, and genetic levels related to acquired behavioral analysis can be obtained.
Hence, behavioral analysis for
C. elegans
enables to connect molecular, cellular, or
genetic levels of mechanism for behavioral regulation.
Additional important characteristic to use
C. elegans
for current biological
research is an excellent affi nity for optical methods including imaging and optoge-
netics. Transparent body already has been afforded powerful methodology for dis-
secting cellular properties: combination with differential interference contrast (DIC)
microscope or genetically labeled fl uorescent probes such as green fl uorescent pro-
tein (GFP) is a prominent case to show experimental merits of
C. elegans
. In addi-
tion, GECIs such as Cameleons (Kimura et al.
2004
; Miyawaki et al.
1997
; Nagai
et al.
2004
) or GCaMPs (Nakai et al.
2001
; Tian et al.
2009
) are key tools for explor-
ing relationship between activity of specifi c neurons and particular behavior.
Transparent body is highly compatible for such imaging probes, and thus making
these probes enable to observe neural activity and behavior simultaneously.
Recently, several kinds of opsin genes are utilized to probe neuronal functions by
specifi c perturbation of cellular ionic current with light (Yizhar et al.
2011
). In such
optogenetic approach of neural networks,
C. elegans
keeps its superiority with its
plenty of cell-specifi c promoters, a complete connection map for all neurons.
As mentioned shortly above, there are immense advantages to use
C. elegans
for
behavioral studies. In this chapter, we describe typical behavioral analysis for
C. elegans
that connects results of genetics, imaging, and other physiological data.
The following sections consist of (1) population analysis, (2) single animal analysis,
(3) calcium imaging with GECIs, and (4) simultaneous monitoring for behavior and
neural activity with highly advanced techniques.
1.2
Population Analysis
Behavioral data often contains stochastic or probabilistic components, which
frequently mask essential characters in observed phenomena. We should then design
behavioral experiments to detect the essence of observed phenomena in spite of
