A histomorphological investigation of the effect of cyclosporin on trabecular bone of the rat mandibular condyle

The effect of cyclosporin A (CSA) on the condylar trabecular bone was evaluated by microscopy. Twenty, 5-week-old male Sprague–Dawley rats were divided into a treated and a control group. Animals in the treated group received CSA, 15 mg/kg body weight, by gastric feeding daily for 4 weeks; controls received the vehicle only. Five animals from each group were killed at the end of weeks 2 and 4. After histological processing, 10 tissue sections from the mid-part of the mandibular condyle were examined. Generally, a histopathological osteopenia was observed around the condyle after CSA treatment, especially at the end of week 4. In the control animals, the trabecular bone volume steadily increased from weeks 2 to 4 (from 0.46±0.07 to 0.61±0.07 mm3/mm3). However, the bone volume was significantly less in the CSA group than in the control group at both times (0.33±0.02 vs 0.46±0.07 and 0.26±0.07 vs 0.61±0.07 mm3/mm3 for CSA vs control group at the end of weeks 2 and 4, respectively). Conversely, an increased marrow volume was observed in the CSA group at both these times (0.60±0.02 vs 0.42±0.08 and 0.71±0.06 vs 0.31±0.06 mm3/mm3 for CSA vs control group at the end of weeks 2 and 4, respectively). Decreases were also observed in trabecular thickness, osteoid seam width, osteoid volume and cortical bone width. Because trabecular bone mass, osteoid mass and cortical bone thickness all showed a decrease after CSA at both times, an inhibitory effect of CSA on trabecular bone formation in the mandibular condyle is proposed.