The crayfish brain
Decapod crustaceans have been studied by many neurobiologists. They have
relatively large and a well-organized nervous system, and show interesting
behavior patterns, ranging from simple reflexes to complex social behavior.
Some stereotypical behavior patterns such as defensive and escape behavior
are mediated by specific sensory input and giant neuromuscular systems.
Therefore, many studies have been conducted, focusing on their stereotypical
behavior patterns. The ventral nerve cord of the crayfish has good longevity
even when isolated; it has been utilized for neurophysiological experiments.
The central nervous system of crayfish is ladder-like (Fig. 1). The anterior-most
ganglion is called the cerebral ganglion. Similar to the insect brain,
the brain of crustaceans, including that of the crayfish, may be regarded
as a ‘microbrain’ in contrast to the brains of vertebrates (‘macrobrain’)
(Mizunami, 2006). The structure of crayfish brains is essentially the same
as that of insects (Fig. 2). Crayfish brain is composed of 3 ganglia fused
together in an anterioposterior direction; these are called the protocerebrum,
deutocerebrum, and tritocerebrum. The left and right structures of them
are connected by commissures. Cell body clusters are located on the
brain surface and divided into 17 (Sandeman, et al., 1992) or 19 (Tautz
and Tautz, 1983) clusters. In addition, the brain is divided
into the neuropils, comprising overlapping dendrites and axon terminals, and the
neural tracts, comprising axon bundles. The neuropils form a major part of the
brain, the part used for processing information.
Fig. 1: Central nervous system of
crayfish (ladder-like ganglia)
Fig. 2: Schematic diagram of the interior of the brain (horizontal
A. horizontal plane
B. sagittal plane
C. transverse plane
Fig.3 Images of crayfish brain sliced in (A) horizontal, (B) sagittal and (C) transverse planes (paraffin, 10µm slices, stained with silver impregnation).
Sandeman D, Sandeman R, Derby C, Schmidt M (1992) Morphology of the brain of crayfish, crabs and spiny lobsters: a common nomenclature for homologous structures. Biol Bull 183:304-326.
Tautz J, Tautz M (1983) Antennal neuropil in the brain of the crayfish:
morphology of neurons. J. Comp. Neurol 218: 415-425.
水波誠 (2006) 昆虫－驚異の微小脳, 中公新書.