Aspects of development of bone marrow in male albino rats: Light and electron microscope study

ABSTRACT

Twenty five healthy male albino rats were utilized in this study to throw more light on the histological and ultra structural changes in femur's bone marrow at different ages in albino rats. They were classified into five groups [5 animals each] group A, [prenatal, 17-19 days of gestation], group B [newborn, I-day old], group C [one week old], group D [adult, 3-6 months old], and group E [senile, more than I8-months old]. The animals were sacrificed and small pieces of femurs were taken and processed for light and electron microscopes examination. The bone marrow was consisted of vascular and non vascular elements. The vascular elements of the prenatal group showed small capillaries and many dilated blood sinusoids. They were lined with flat endothelial cells with little cytoplasm. Large cells[adventitial cells] with large nuclei, pale cytoplasm and long processes were noticed on the abluminal side of dilated sinusoids in the marrow of the newborn. The marrow arterioles of 1 week- old and adult groups were lined with cuboidal lining cells and surrounded by pericytes with flat nuclei and long processes. However, in the senile group, multiple thick walled arterioles with narrow lumen were detected. The non vascular elements of the marrow were formed of hemopoietic and non hemopoietic cells. In the prenatal group, some cells showed small electron dense nuclei, dense cytoplasm and irregular cell membrane [apoptotic cells]. Many large macrophages with eccentric nuclei were seen in cIose relation with the apoptotic cells. Giant cells with multiple nuclei and vacuolated cytoplasm [osteoclasts] were noticed adjacent to calcified spicules. Many hemopoietic cells at different stages of development were noticed at 1-day of age. Apoptotic neutrophils with dark nuclei and muddy cytoplasmin together with mitotic cells were also observed. Hemopoietic cells were markedly increased at the age of I-week, adult, till senile. Fat cells and many megakaryocytes were also marked. The megakaryocytes appeared as large cells with multilobulated nuclei and numerous electron dense granules in their cytoplasm. Also, intracytoplasmic canaliculi appeared as elongated vesicles which may branch. These canaliculi were of smooth surface and enclosed empty cores. With senility, there was marrow hypocellularity. Most of the cells were apoptotic. In conclusion, bone marrow started its function as a hemopoietic organ postnatally. In senile group apoptosis predominated mitosis. Predominance of mitosis in young ages making them more recommended as a potent source for bone marrow transplantation