الفهرس 
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Abstract
The present work was designed to investigate the age related structural changes in olfactory bulb of rabbits, it is hoped that the study will provide data for further correlative work with functional modalities of olfaction.A total number of twelve male baladyrabbits were used. They were divided into two groups; each group consisted of six rabbits:
Group I:Adult male rabbits aging from 7-10 months, weighting 1.5-2kg.Group II: Senile male rabbits aging 30-36 months, weighting 2.5-3kg.
The heads of all rabbits were cut by a razor blade. The olfactory bulbs were fixed in Bouin’s solution for ten days then paraffin blocks and coronal sections were performed from one olfactory bulb of each group and stained with hematoxylin and eosin. The other olfactory bulb was used to prepare epon blocks.Semithin and ultrathin sections were cut and examined under the light and electron microscope. In hematoxylin and eosin stained sections, the total width of olfactory bulb layers and width of different layers were measured in six specimens of group1 and compared to 6 specimens of group2. The maximum diameter of glomeruli,the number of glomeruli and mitral cells were counted. The means and standard deviations of all measurements were recorded and the results were tabulated and analyzed using the independent T test.There was statistically significant difference between group 1 and group2 as regard the mean total width of all layers, width of glomerular layer, external plexiform layer,mitral cell layer, internal plexiformlayer, mean number of the glomeruli, mean number of mitral cells and maximum diameter of glomeruli.There was no statistically significant difference between group 1 and group 2 as regards the mean width of olfactory nerve fibers layer and granular celllayer.Histological examination of the olfactory bulbs of group 1 revealed that the olfactory bulb was easily identified in coronal sections by its characteristic glomeruli and mitral cells. The olfactory nerve fibers layer was the most superficial layer of the olfactory bulb and contained ensheathingcells, followed by the glomerular layer in which glomeruli were surrounded by periglomerularinterneurons, then outer plexiform layerthat wasbounded deeply by the mitral cell layer. Mitral cells in the mitral cell layer arranged in a single widely spaced row of neurons. Mitral cells were large pyramidal cells characterized by their vesicular nucleus, with long apical dendrite and an axon. A thin internal plexiform layer wasobserved deep to the mitral cell layer separating it from thegranular cell layer.
Histological examination of the olfactory bulbs of group 2 revealed that the six layers of the olfactory bulb were identified. Glomeruli appeared smaller, not compact and shrunken. There wereperiglomerularvacuolations. Mitral cells appeared degenerated darkly stained with wide pericellularspace, irregular cell membrane, interrupted apical dendrite and vacuolated cytoplasm. The granular cell layercontainedamalgamated groups of granule cellswith spacing around the cells,shrunken dark cells and small vacuolations.
Electron microscopic study of periglomerular cell showed clumping of nuclear chromatin, peripheral arrangement of chromatin,irregular separated nuclear membrane. Their cytoplasm contained multiple vacuoles, distorted mitochondria and apparent increase inlysosomes and lipid pigments.
Electron microscopic study of mitral cells showed rounded mitral cell nuclei with clumped islets of chromatin and peripheral arrangement of chromatin, patchy separation of nuclear membranes with nuclear membrane irregularity, vacuolated cytoplasm showing: distorted mitochondria, cisternae of rough endoplasmic reticulum. There were apparent increase in the lysosomes and lipid pigments. Some myelinated nerve fibers revealed separation between lamellae of myelin sheath and interrupted myelin sheath.