The development of the olfactory mucosa in the mouse : electron microscopy

Abstract

In a previous paper we outlined the chief events occurring in the development of the olfactory organ in mice as seen with the light microscope (Cuschieri & Bannister, 1974); although these observations provide a broad description of cytological changes, many details of cell differentiation require the use of the electron microscope for their study. The olfactory epithelium possesses many of the structural characteristics of the central nervous system, since it contains the cell bodies of neurons which develop in situ from the ectodermal cells of the olfactory placode in a manner reminiscent of the origin of neuroblasts in the neural tube. Light microscope studies indicate that the differentiation of the placode is a complex matter, for during fetal development a number of distinct types of non-neural cell are formed in addition to the receptors. The development of the olfactory epithelium is also related to the ontogeny of the neighbouring olfactory bulb, into which the central ends of the olfactory axons grow to synapse with second-order neurons at about the 12th day of gestation in mice (Hinds, 1972a, b; Hinds & Hinds, 1972). In view of the interesting problems associated with the development of the olfactory epithelium it is surprising that the ultrastructural changes have been so little studied. A few short accounts of certain aspects of olfactory epithelial development have been published recently (Breiphol, 1972; Breiphol, Laugwitz & Bornfeld, 1974; Breiphol, Mestres & Meller, 1973) and early postnatal changes have also been mentioned by Frisch (1967) and by Seifert & Ule (1967), but no overall account of the various stages of fetal olfactory organ development has so far been given. The present observations concern the development of the olfactory epithelium and olfactory axons from the 10th day of gestation until the postnatal period, and deal with some of the important cytological changes occurring during this time.