Dexamethasone reduces the expression of p75 neurotrophin receptor and apoptosis in contused spinal cord

Apoptosis is an important cause of secondary cell death in spinal cord injury (SCI). SCI induces the expression of the low affinity neurotrophin receptor p75 (p75NTR), that in the absence of the high affinity component, TrkA, can promote cell death by apoptosis. We therefore hypothesized that a reduction of p75NTR expression in SCI may increase tissue sparing and therefore improve recovery of function. As a tool to test our hypothesis we used the synthetic glucocorticoid dexamethasone (DEX) to down-regulate p75NTR expression. A standardized thoracic spinal cord contusion injury was produced in female rats. Laminectomized and SCI rats received various doses of DEX immediately after injury and the treatment was continued daily for 7 days. DEX, given at high doses (20 mg/kg, s.c.) but not at low doses (1 or 8 mg/kg) prevented the increase in p75NTR mRNA and protein in SCI rats, without affecting the expression of TrkA. High doses of DEX also reduced cellular apoptosis both in white and gray matters. This effect correlated with the ability of DEX to accelerate behavioral recovery of function measured by a combined behavioral score. These data suggest that reduction of p75NTR in SCI may be a therapeutic strategy to limit cell and tissue damage and therefore to improve recovery of function in SCT patients. (C) 2001 Elsevier Science B.V. All rights reserved.