Organization of diencephalon of the sturgeons. Posterior tubercular area. Caudal region

Cytoarchitectonics of caudal region of the posterior tubercular area of diencephalon was studied in four species of the true sturgeons: the giant sturgeon, Huso huso L., Kura sturgeon, Acipenser güldenstädtii persicus n. Kurensis Belyaeff, stellate sturgeon, Ac. stellatus Pall. and the barbel sturgeon Ac. nudiventris Lov. Morphologic organization of the brain region was studied by using staining techniques of Nissl and Bielschowski (Viktorov’s modification). Five nuclei were identified in the caudal region of the posterior tubercular area in all studied species: caudomedial, caudal and lateral thalamic nuclei forming the medial group, as well as lateral torus and posterior thalamic nuclei forming the lateral group. The latter two nuclei have their subdivisions. Characteristic peculiarity of the caudal region is the presence of only migrated nuclei. It is concluded that the level of differentiation of the diencephalon posterior tubercular area of the sturgeons allows considering it as one of the most evolutionary advanced structures among those in the actinopterygian fish line.