Why Ligia?
Crustaceans have long served as exellent animals for
physiological experiments: Expecially for investigations in neuroscience
and neuromuscular physiology.
It is well known that crustaceans have neurogenic heart.
The cardiac ganglion (CG; a cluster
of neurons on the heart wall) serve as the heart pacemaker,
producing rhythmic motor outputs for the cardiac muscle. Since the early
anatomical studies by J. S. Alexandrowicz, CG has been one of the
best understood local neural networks in crustacean nervous system.
Recently,
it has been found that not all of crustaceans have the neurogenic heart,
but rather there are diverse pacemaker mechanisms. Hiroshi Yamagishi
(Univ. of Tsukuba) reported
the myogenic heartbeat in the primitive crustacean, Triops
longicaudatus (Notostrace, Branchiopoda). He also had shown in
the isopod Ligia that the cardiac muscle posseses myogenisity
whose activity is driven to faster neurogenic rhythm by the cardiac ganglion.
Moreover, the most exciting thing he found was that during the embryonic
development of Ligia, the heart pacemaker mechanism changes from
myogenic to neurogenic!!!
I was interested in the nervous regulation
of this unique heart in Ligia. How they produce normal heartbeat?
How the heart is regulated before and after the pacemaker switching during
the development? This is why I got so crazy about this animal.
Indeed, I also found that they're really nice guys!
Next:
*All figures are originally drawn by Dr. H. Yamagishi (Univ.
of Tsukuba, Japan) and modified by A. Sakurai.