The histochemical and cytochemical changes from formative to resorptive osteocytes

Based on their ultrastructural features, osteocytes have been classified in to three phases: formative, resorptive, and degenerative. However, the mech anism of the morphological changes from formative osteocyte to resorptive o steocyte is still unclear. Therefore, we labeled bone matrix with calcein a nd examined chronologically the histochemical changes in osteocytes from tw o distinct areas in the mandible, focusing on the relationship between oste ocytes and osteoclastic bone resorption. Tartrate-resistant acid phosphatas e (TRAP) activity was detected only in osteocytes located near sites of ost eoclastic bone resorption. Osteocytes far from osteoclasts lacked TRAP acti vity, even those that had been enclosed in bone matrix as long as the osteo cytes that did show TRAP activity. Furthermore, glycogen granules evidenced by periodic acid-Schiff and the periodic acid-thiocarbohydrazide-silver pr otein staining in osteocytes disappeared when the cell acquired TRAP activi ty. These findings suggest that the acquisition of TRAP activity in an oste ocyte is closely synchronized with bone resorption. Disappearance of glycog en in osteocytes in the same area may also be related to the acquisition of TRAP activity or bone resorbing activity. The osteocytes characterized by glycogen accumulation must be in the phase that follows the formative phase , in which osteocytes display neither formation nor resorption activity.