Functional regeneration of sensory axone into the adult spinal cord

The arrest of dorsal root axonal regeneration at the transitional zone betw een the peripheral and central nervous system has been repeatedly described since the early twentieth century(1). Here we show that, with trophic supp ort to damaged sensory axons, this regenerative barrier is surmountable. In adult rats with injured dorsal roots, treatment with nerve growth factor ( NGF), neurotrophin-3 (NT3) and glial-cell-line-derived neurotrophic factor (GDNF), but not brain-derived neurotrophic factor (BDNF), resulted in selec tive regrowth of damaged axons across the dorsal root entry zone and into t he spinal cord. Dorsal horn neurons were found to be synaptically driven by peripheral nerve stimulation in rats treated with NGF, NT3 and GDNF, demon strating functional reconnection. In behavioural studies, rats treated with NGF and GDNF recovered sensitivity to noxious heat and pressure. The obser ved effects of neurotrophic factors corresponded to their known actions on distinct subpopulations of sensory neurons. Neurotrophic factor treatment m ay thus serve as a viable treatment in promoting recovery from root avulsio n injuries.