Morphology, Morphometry and Neuroanatomy of the Olfactory Epithelium and the Olfactory Bulb of a Featherback Fish, Notopterus notopterus.

Olfactory organs of fishes show wide range of variations depending upon the systematic groups and ecological habitats. Number, shape and arrangement of the lamellae vary considerably among different teleosts ranging from flat unfolded surface to multi-lamellar rosette. Objective of the present work was to study the organization of olfactory system of Notopterus notopterus. As it is demersal in habitat, olfaction is expected to play a prominent role in various life processes. With the help of Haematoxylin-Eosin and Kluver and Barrera (1953) staining techniques, organization of the olfactory epithelium and olfactory bulb was studied. In N. notopterus, olfactory epithelium is a multilamellar structure comprising 70-76 lamellae radiating from a median raphe. Each lamella comprises sensory and nonsensory regions. Sensory region shows ciliated, microvillous, crypt receptor cells, supporting cells and basal cells. Nonsensory region has ciliated nonsensory cells, basal cells and mucous cells. Within the median raphe, distinct melanophores innervated by axons from olfactory receptor neurons are observed. Olfactory epithelium is connected to the bulb by a short olfactory nerve. Olfactory bulb is a concentrically arranged four layered structure with olfactory nerve layer on the outermost side followed by glomerular layer, mitral cell layer and granular cell layer. Ruffed cells are observed surrounding the mitral cells. In dorsomedial region of the olfactory bulb, giant cells of nervus terminalis are prominent. In the present study, fiber projections from the olfactory receptor neurons to ventral telencephalon are clearly demonstrated histologically, indicating the pathway of chemosensory signal from olfactory receptor neurons to the higher brain areas. This work will be useful to study the neuroanatomy of the olfactory system and ultimately to understand neurobiology of fish olfaction.