Glycoconjugate expression in the olfactory bulb of the premetamorphic larva of the Japanese sword-tailed newt (Cynops ensicauda)

Abstract

We examined the organization of the olfactory organ and assessed the lectin histochemistry to investigate the glycoconjugate distribution of the olfactory bulb in premetamorphic larvae of Cynops ensicauda. The nasal cavity was an oval chamber that contained olfactory epithelium and a primitive vomeronasal organ. Secretory products were found in the supporting cells of the two sensory epithelia and in the respiratory cells. Ten lectins bound to the olfactory and vomeronasal nerve fibers as well as to the glomeruli in the olfactory bulb. The binding intensity in larvae was weaker than that reported previously in mature animals. This difference suggests a functional correlation between the expression change of glycoconjugates and the developmental refinement of the olfactory system during metamorphosis.

Keywords: lectin; metamorphosis; olfactory system; salamander; vomeronasal organ.

Fig. 1.

Transverse sections of the olfactory organ of larval Cynops ensicauda. The left and top sides of panels (a, c) are lateral and dorsal portions, respectively. (a, b) Hematoxylin-eosin staining. In stage 58 larvae, the olfactory and vomeronasal epithelium (OE; arrows, and VNE; arrowhead) were partitioned by ridges of nonsensory epithelium (asterisks). Nuclei of supporting, receptor, and basal cells (SC, RC and BC) were located in the upper, middle, and basal regions of the OE and VNE, respectively. onf, olfactory nerve fibers. (c, d) Periodic acid-Schiff (PAS) staining. In both the OE and VNE, PAS reaction was found in the free border (insets in panel (d)) and the supranuclear region of the supporting cells. Respiratory cells in ridges were also positive with PAS (asterisks). Scale bars: 100 µm (a, c), 25 µm (b, d).

Fig. 2.

Hematoxylin-eosin staining and lectin bindings in the main and accessory olfactory bulb (MOB and AOB) of larval Cynops ensicauda. The left and top sides of each panel indicate the rostral and lateral portions in hemispheres of the telencephalon, respectively. (a) Horizontal section of the olfactory bulb, stained with hematoxylin-eosin. The olfactory and vomeronasal nerves (ON and VN) terminated in the glomeruli of the MOB (MOB-GL) and in those of the AOB (AOB-GL), respectively. (b–h) LEL (b) and SBA (c) exhibited a different binding intensity between the MOB and AOB. BSL-I (d) and PNA (e) showed a different preference for binding between the nerve and glomerular layers. WGA (f), s-WGA (g), and PSA (h) bound with a uniform labeling to the ON and VN and to the MOB-GL and AOB-GL. Arrows in the panels represent the border between the MOB and AOB. Scale bar: 100 µm.