Scanning electron microscopic observations of rat tibia using the HCl-collagenase method.

The metaphysis of rat tibia was examined by scanning electron microscopy (SEM) using the HCl-collagenase method (EVAN et al., 1976) and the three-dimensional structure of osteocytes and the relationship between osteocytes and osteoblasts were demonstrated. After the HCl-collagenase treatment, the bone matrix near the exposed surface was completely removed but the cellular components retained their structural integrity. Young osteocytes located close to osteoblasts showed flattened, spindly shapes. They were connected with adjacent osteoblasts by short, wide and slightly branched processes. On the other hand, the osteocytes located in the deeper portion of trabecular bone were smaller in size, being round or oval and flattened in shape. They were connected with both osteoblasts and neighboring osteocytes by long and more extensively branched processes forming a complicated network. From these results, it is suggested that osteoblasts extend their processes perpendicularly to the bone surface, with these processes branching off and connecting to each other at the osteoid layer.