Lectin histochemical analysis of the olfactory bulbs in the barfin flounder (Verasper moseri)

Several lines of evidence have shown that the olfactory system of the fish contains the main and accessory olfactory systems. However, morphological data indicate that the accessory olfactory bulb, the primary centre for the accessory olfactory system, will not differentiate in the fish. Therefore, the fish olfactory bulb is supposed to engage in both main and accessory olfactory systems. To examine this possibility, we investigated the olfactory bulb of the barfin flounder (Verasper moseri) by histochemical examination using lectins. The olfactory bulb of the barfin flounder showed a laminar structure with four layers, and diffuse glomerular architecture was observed in the glomerular layer. Based on the expression patterns of sugar residues, the glomerular layer of the barfin olfactory bulb was largely divided into three portions. Heterogeneity in the lectin-binding pattern among olfactory glomeruli was clearly demonstrated by the fluorescent double-lectin staining. The results of this study suggest that the fish olfactory bulb contains both regions equivalent to the main and accessory olfactory bulbs, and they are subdivided into small subsets with different functions.