The three dimensional architecture of the rat femur bone marrow stroma was observed by scanning electron microscopy. The bone marrow was fixed and vibrated by ultrasonication to dislodge the hematopoietic cells embedded in the meshes of the marrow reticulum. The stromal reticulum was exposed, while its three dimensional architecture was preserved.
The marrow stromal reticulum consisted of intersinusoidal reticular cells and perivascular reticular cells (adventitial cells), and a small amount of reticular fibers. Two types of meshwork were noted in the bone marrow reticulum. Each mesh of one type was the size of one hematopoietic cell. This meshwork consisted of short and broad or stout cytoplasmic processes. A hematopoietic cell was enwrapped by attenuated cytoplasmic sheaths of the reticular cells and sequestered from the surrounding hematopietic cells. The other type of meshwork was composed of straight running, long and slender filopodia of the reticular cells. Several hematopoietic cells were tightly packed in each mesh of the meshwork of this type, thus presenting a polyhedral appearance. Attenuated adventitial cells enveloped the marrow blood vessels, and were connected with each other by their sheath-like cytoplasmic processes but round, variously sized intercellular spaces remained. The intersinusoidal reticular cells extended their processes to the adventitial cells and the adventitial cells also stretched their processes to the intersiusoidal reticulum.
