Effect of chemical sympathectomy with 6-hydroxydopamine on osteoclast activity in the gerbilline middle ear bulla

Hypothesis: Chemical sympathectomy with 6-hydroxydopamine (HDA) increases m iddle ear bulla bone resorption in the Mongolian gerbil. Background: Many diseases of the middle ear have pathologic processes linke d to abnormal bone remodeling. Numerous factors controlling bone remodeling have been identified. An understanding of these factors and their role in pathologic remodeling is therefore essential. Sympathectomy, induced both s urgically and pharmaceutically, is known to increase middle ear bone resorp tion. suggesting a role for the central nervous system in bone metabolism. This effect, however, may be confounded by hemodynamic changes induced by h emicranial surgical sympathectomy or by uncertainty in the action of pharma ceutical agents on the sympathetic nervous system. In this experiment, a th ird modality with unique properties, chemical sympathectomy with HDA, was u sed to quantify further the effect of sympathectomy on middle ear bone remo deling. Methods: Eight gerbils designated experimental received in traperitoneal in jections of HDA (75 mg/kg) for 1 week, whereas eight animals designated con trol received similar injections of saline. One week after injections, the animals were euthanized and bulla bone samples were analyzed histomorphomet rically to determine osteoclastic activity. In addition, to assess for any direct effects on bone metabolism, the activity of HDA was determined in vi tro using the calvarial calcium re lease assay. Results: The in vitro study found HDA to have no direct stimulatory activit y on calcium release. The in vivo study showed HDA to increase osteoclastic activity significantly in middle ear bone. Conclusion: HDA-induced sympathectomy increases bone resorption in gerbilli ne middle ear bone.