Brain Atlas of the Japanese Eel: Comparison to Other Fishes

The whole brain atlas of the eel was constructed in the first place by Klüver-Barréra’s staining. Eighty one nuclei and thirty fiber tracts were identified in the present study. Basically, the brain topology of the eel was similar to that of the rainbow trout, the goldfish, the zebrafish, and the catfish. However, some details differed from those of other teleosts. The parvocellular preoptic nucleus (PP) was not subdivided, whereas the anterior PP is distinguished from the posterior part in the zebrafish and the rainbow trout. The intermediate thalamic nucleus was not distinguished, whereas it is identified in the zebrafish, the goldfish, and the rainbow trout. The paraventricular organ (PVO) was single, while paired PVOs are observed in the zebrafish. The torus semicircularis (TS) was smaller than that in the goldfish and rainbow trout. The cell size of the nucleus of medial longitudinal fascicle (NMLF) in the tegmentum was larger than that in the glass knifefish and the zebrafish. The protrusion of the nucleus lateralis valvulae (NLV) into the mesencephalic ventricle (VMes) was larger than that in the zebrafish and the rainbow trout. The valvula cerebelli was smaller than those in the goldfish and the zebrafish. The facial lobes (LVII) ran through the medulla oblongata (MO), whereas the two lobes fuse at the caudal cerebellum in the goldfish, the catfish, and the zebrafish. The expansion of the vagal lobe (LX) in the caudal MO was smaller than that in the goldfish and the zebrafish. The glossopharyngeal motor nucleus (MNIX) and the vagal motor nucleus (MNX) were fused to make a columnar structure named glossopharyngeal-vagal motor complex (GVC). Such a columnar complex seems to be common in fishes, since similar columns are observed in the lamprey, the elasmobranch and other teleost fishes. The facial motor nucleus (MNVII) was separated from the GVC, whereas it is fused with the GVC in the sturgeon, the reedfish and the tarpon.