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Abstract
The present study described the olfactory epithelium of postnatal rats using both light and electron microscope either transmission or scanning electron microscopy, also the study described the olfactory bulb and tract of the rat using light microscope.
This study showed that the olfactory epithelium was formed of cells arranged into superficial, middle and deep layers and underlying lamina propria. The superficial layer was formed of the dendrites of olfactory receptor cells and the supranuclear parts of the supporting cells, while the middle layer included the nuclear parts of olfactory receptor cells; the deep layer was formed of the basal cells. The lamina propria includes the olfactory nerve bundles, bowman’s glands and connective tissue cells.
There was marked increase in the thickness of olfactory epithelium form the age of newborn till the age of six months with maximal increase at the age of seven days. The arrangement of the nuclei of the supporting cells and olfactory receptor cells was obvious in the development till the adult age, and then nuclei were intermingled with each other in the old age. Also there was marked increase in thickness of lamina propria mainly due to increased diameter of olfactory axons.
The laminar pattern of the olfactory bulb was not well developed in the newborn age and was only formed of olfactory nerve layer, the external plexiform layer, the mitral cell layer, the inner plexiform layer, the granule cell layer and subependymal layer. With the progress of development, the laminar pattern of the bulb started to be arranged. At the age of 7days the glomerular layer appeared to be well formed with marked demarcation between the mitral and the inner plexiform layer. At the sixteen days age and adult age, there is marked increase in thickness of the mitral, glomerular, outer plexiform and granule layers. The mitral layer was the most rabidly developed one in relation to other layers. In old age there was marked decrease in the thickness of the epithelium with marked deterioration of the laminar pattern especially among the mitral and inner plexiform layers.
The olfactory receptor cells were bipolar cells with peripheral and central processes. The peripheral one extended outwards towards the surface of the cell and projecting as olfactory knobs. On the other hand, the central processes extended into the deep layers of the epithelium towards the basal layer. The cytoplasm of the cell contained numerous elongated mitochondria and heterochromatic nuclei surrounded by scanty cytoplasm and few cell organelles. The olfactory knobs showed many cilia projecting over its surface.