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Structure of the nerve plexus in the red swamp crayfish (Procambarus clarkii)


Katsushi Kagaya (Duke University)


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 plane)




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).


References

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.



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