Functional regeneration of sensory axons into the adult spinal cord.

The arrest of dorsal root axonal regeneration at the transitional zone between the peripheral and central nervous system has been repeatedly described since the early twentieth century. Here we show that, with trophic support 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 selective regrowth of damaged axons across the dorsal root entry zone and into the spinal cord. Dorsal horn neurons were found to be synaptically driven by peripheral nerve stimulation in rats treated with NGF, NT3 and GDNF, demonstrating functional reconnection. In behavioural studies, rats treated with NGF and GDNF recovered sensitivity to noxious heat and pressure. The observed effects of neurotrophic factors corresponded to their known actions on distinct subpopulations of sensory neurons. Neurotrophic factor treatment may thus serve as a viable treatment in promoting recovery from root avulsion injuries. I