Flunarizine enhances survival and regeneration of sensory and motor neurons after peripheral nerve injury

The diphenylpiperazine, flunarizine, partially prevents apoptosis after trophic factor deprivation in neural crest-derived neurons. Flunarizine protects dorsal root ganglion neurons (DRG) after nerve growth factor (NGF) withdrawal in vitro and after peripheral nerve injury in newborn rats in vivo. We have further studied the mechanisms of neuronal protection by flunarizine. Oligosomal DNA fragmentation, a hallmark of apoptosis, was significantly decreased by treatment of DRG neurons with flunarizine after NGF deprivation. We examined the effect on survival of the timing of administration of flunarizine to DRG neurons both in vitro and in vivo. Flunarizine effectively rescued dissociated DRG neurons if administered up to six hours after NGF withdrawal. In vivo, flunarizine prevented DRG neuronal death after sciatic axotomy in newborn rats if given soon after injury. Long-term experiments were done to test the ability of flunarizine to protect neurons and enhance regeneration after sciatic nerve injury. Newborn rats were subjected to peripheral nerve injury and administered flunarizine for four weeks; no further treatment was given for an additional 12 weeks. The group treated with flunarizine demonstrated a significantly increased number of DRG and spinal motor neurons that had regenerated axons into the distal sciatic nerve as determined by retrograde labeling with HRR Myelinated axons in the sural nerve in the group treated with flunarizine increased by nearly two-fold compared to control animals. Thus, flunarizine was able to enhance survival and promote long-term regeneration of sensory and motor spinal neurons after peripheral nerve injury.