No Signature of Osteocytic Osteolysis in Cortical Bone from Lactating NMRI Mice.

The roles of osteocytes in bone homeostasis have garnered increasing attention since it has been realized that osteocytes communicate with other organs. It has long been debated whether and/or to which degree osteocytes can break down the bone matrix surrounding them in a process called osteocytic osteolysis. Osteocytic osteolysis has been indicated to be induced by a number of skeletal challenges including lactation in CD1 and C57BL/6 mice, whereas immobilization-induced osteocytic osteolysis is still a matter of controversy. Motivated by the wish to understand this process better, we studied osteocyte lacunae in lactating NMRI mice, which is a widely used outbred mouse strain. Surprisingly, no trace of osteocytic osteolysis could be detected in tibial or femoral cortical bone either by 3D investigation by synchrotron nanotomography, by studies of lacunar cross-sectional areas using scanning electron microscopy, or by light microscopy. These results lead us to conclude that osteocytic osteolysis does not occur in NMRI mice as a response to lactation, in turn suggesting that osteocytic osteolysis may not play a generic role in mobilizing calcium during lactation.