Identification of Tufted Cells in the Olfactory Bulb

Abstract

WE do not know whether two different types of secondary olfactory neurones exist. Classical anatomical studies have separated secondary olfactory neurones into two types: tufted cells and mitral cells¹. Mitral cells form a discrete layer in the olfactory bulb and send their axons by way of the lateral olfactory tract (LOT) to ipsilateral cortical structures. Tufted cells are smaller than mitral cells and are scattered throughout the external plexiform layer. The efferent path of tufted cell axons is not clear. Previously, tufted cell axons were thought to cross by way of the anterior limb of the anterior commissure (AAC) and terminate in the contralateral olfactory bulb¹, but recent anatomical studies^2,3 do not confirm the entrance of tufted cell axons into the AAC. There are now at least two different views about the projection of tufted cell axons. Lohman and Mentink⁴ propose that tufted cell axons enter the LOT and that, therefore, at least some tufted cells may be considered displaced mitral cells. Valverde⁵, however, states that tufted cell axons do not leave the olfactory bulb.