The structure and histochemistry of the olfactory and vomeronasal organs in the mouse

Abstract

Morphological and histochemical studies using light and electron microscopy have been carried out on the olfactory and vomeronasal organs of albino mice during development in adult life. At 10 days gestation, the earliest morphological evidence of differentiation of olfactory receptors from the cells of the olfactory placode is the outgrowth of centrally directed axonal process, followed at 11 days by differentiation of olfactory dendrites ending in ciliated knobs at the epithelial surface. Further morphological changes leading to the maturation of the olfactory receptors occur in the receptor perikaryal after the 17th day of gestation. During development, olfactory receptors are situated in juxtaposition to one another but become isolated by supporting cells in the adult. Morphological differentiation of supporting and basal cells and of Bowman’s glands is first evident on the 17th day of gestation. In the adult vomeronasal sensory epithelium the receptors are incompletely separated from one another by supporting cells, cilia are not present on their terminal knobs and typical basal cells and Bowman’s glands are absent. The histochemical distribution of enzymes alkaline phosphatase, acid phosphatase, Ca++ adenosine triphosphatase, succinic dehydrogenase, cytochrome oxidase and non-specific esterase in the adult olfactory and vomeronasal epithelia and the changes in their pattern of distribution during development have been investigated. The levels of activity of the first four enzymes at various developmental ages have been compared using microdensitometric methods. The presence of a neutral mucosubstance within the olfactory and vomeronasal receptors has also been described. The olfactory surface fluid and the secretions of Bowman’s glands have been characterised histochemically and found to contain a sulphated mucosubstance, in contrast to the secretions of the other nasal glands which contain either a neutral mucosubstance or sialomucins. The morphological and enzymatic characteristics of the olfactory and vomeronasal organs are discussed in relation to their possible functions.