Osteocytes are surrounded by hard bone matrix, and it has not been possible previously to directly observe the in situ architecture of osteocyte morphology in bone. Electron microscope tomography, however, is a technique that has the unique potential to provide three-dimensional (3D) visualization of cellular ultrastructure. This approach is based on reconstruction of 3D volumes from a tilt series of electron micrographs of cells, and resolution at the nanometer level has been achieved. We applied electron microscope tomography to thick sections of silver-stained osteocytes in bone using a Hitachi H-3000 ultra-high voltage electron microscope equipped with a 360° tilt specimen holder, at an accelerating voltage of 2 MeV. Osteocytes with numerous processes and branches were clearly seen in the serial tilt series acquired from 3-μm-thick sections. Reconstruction of young osteocytes showed the 3D topographic morphology of the cell body and processes at high resolution. This morphological data on osteocytes should provide useful information to those who study osteocyte physiology and the several models used to explain their mechanosensory properties.

The number and distribution pattern of silver staining nucleolar organizer regions (AgNORs) were thought to reflect the cellular proliferative activity and the malignancy of tumours. Using a silver-staining method, the variations of AgNORs have been studied in patients with atypical inflammatory lesion (n = 5), malignant reticulosis (n = 5) and Wegener's granulomatosis (n = 6). Our results reveal that there was a statistically significant difference (p<0.01), highly suggestive of a difference in AgNOR counts between the atypical inflammatory lesion and Wegener's granulomatosis, with the Wegener's granulomatosis specimens having the higher irregular AgNORs, but the difference between Wegener's granulomatosis and malignant reticulosis is probably not clinically important. It is concluded that AgNORs may be useful in differentiating Wegener's granulomatosis from an atypical inflammatory lesion, and the simplified counting technique is adequate for the purpose.