Co-expression of nerve growth factor and p75NGFR in the inferior alveolar nerve after mandibular distraction osteogenesis

During mandibular distraction osteogenesis (DO), the inferior alveolar nerve (IAN) is damaged during distractor activation, but spontaneously recovers during consolidation. Although many neurotrophic factors are known to play critical roles, there have been few studies on the mechanism of peripheral nerve recovery after DO. The aim of this study was to observe the expression pattern of p75NGFR (low-affinity receptor of NGF) and to detect autocrine growth activity in IANs following mandibular DO. Unilateral mandibular distractions (0.5 mm each, twice per day for 10 days) were conducted on eight mongrel dogs. Two each were killed at 7, 14, 28 and 56 days after completing distraction. The distracted IAN and contralateral control nerve were harvested. Immunohistochemical staining was performed to determine p75NGFR expression, and double immunofluorescent staining to detect NGF and p75NGFR co-expression. Levels of p75NGFR expression were found to be significantly elevated at 7 and 14 days in Schwann cells located in the outer layer of axon, but were almost undetectable at 28 and 56 days. In double immunofluorescent images, the co-expression of NGF and p75NGFR was also detected at 7 and 14 days. p75NGFR plays an important role in remyelination due to its abundant expression in Schwann cells of damaged nerves, and NGF is an autocrine growth factor present in distracted IANs during the early consolidation period after mandibular DO.