Neuronal organization of the olfactory bulb in the hagfish, Eptatretus burgeri: a Golgi study

The neuronal organization of the olfactory bulb (OB) in the hagfish (Eptatretus burgeri) was studied using the rapid Golgi method. Cytologically, two groups of cells, the mitral and stellate cells, were discernible in the OB. Cytoarchitecturally, the OB showed a distinct laminar structure. From the periphery inward, the following four strata were distinguished: the stratum nervosum, stratum glomerulosum, stratum mitrale and stratum stellatum. Olfactory fibers from the olfactory epithelium reach the rostral aspect of the OB and form the stratum nervosum. The olfactory fibers run deeply in the OB, enter the stratum glomerulosum and terminate in the olfactory glomeruli which are arranged in three to four rows. Numerous mitral and a few stellate cells are distributed in periglomerular areas. The dendrites of the mitral cells terminate in one to two glomeruli in tufted terminals, while those of the stellate cells are distributed in periglomerular areas. The stratum mitrale also consists of mitral and stellate cells. The mitral cells in this stratum extend long dendrites to 4-5 widely separated glomeruli and generate axons traveling caudally. The dendrites of the stellate cells are long and are distributed in the stratum glomerulosum and stratum stellatum, as well as within the stratum mitrale. The stratum stellatum occupies a narrow caudal area and consists mainly of stellate cells extending long dendrites to the stratum stellatum and stratum mitrale.