Rapid induction of localized bone resorption in the auditory bulla of the Mongolian gerbil, Meriones unguiculatus, by increased air pressure.

Osteoclastic bone resorption can be induced within the auditory bulla of the Mongolian gerbil by minute increases in air pressure. The objective of this study was to determine the rate at which osteoclasts are induced in areas of resorption and to compare the rate of osteoblast recruitment. Stainless steel tubes were implanted into the middle ears of 31 male gerbils through which a static pressure of 10 mm Hg above atmospheric was applied. The animals were killed at intervals (0, 1, 2, 4, 6, and 8 days) and the ventral wall of the bulla was studied histomorphometrically. The osteoclast area and osteoclast number were measured along the inner surface of the bone of the bulla; the activity of osteoblasts of the outer surface was also estimated. A significant increase in osteoclasts was found over time (P less than 0.0001). There was no significant increase in osteoclasts at 1 day (P = 0.5) but at 2, 4, 6, and 8 days there was a significant increase (P less than 0.03). Osteoblast activity on the outside of the bulla wall paralleled osteoclast activity. In this quantifiable, experimental system, a localized modeling process may be induced within 2 days without the confounding elements of localized trauma or inflammation inherent in other models of localized bone remodeling.