Neurogenic pathway mediated remote preconditioning protects the brain from transient focal ischemic injury

Attenuation of ischemic injury can be achieved by priming the brain with a sub-lethal ischemic insult, a phenomenon known as ischemic preconditioning (IP). We sought to determine if subjecting a distant organ, such as the lower limb, to a similar priming ischemic insult would result in protection of the brain from a subsequent severe ischemic injury, as induced by middle cerebral artery occlusion (MCAo) and if this protection is mediated via a neurogenic pathway. Adult Wistar male rats were subjected to either remote preconditioning (RPC) or sham surgery and then subsequently underwent 2 h MCAo 24, 48 or 72 h after the RPC/sham RPC stimulus. Of the animals undergoing RPC, only those that sustained MCAo 24 h later showed significantly smaller cerebral infarct volumes (150.34±30.91 mm(3)) and better clinical neurological outcomes (1.15±0.69) as compared to the sham RPC group (infarct volume 250.25±26.98mm(3); neurological score 1.80±0.87) (P<0.05). RPC animals sustaining MCAo at 48 and 72 h later did not show significant differences in cerebral infarct volumes or clinical neurological outcomes as compared to the sham RPC group. Furthermore, attenuation of the neuroprotective effect by the ganglion blocker hexamethonium suggested a neurogenically mediated pathway responsible for this phenomenon. Remote sub-lethal ischemic injury to both lower limbs results in cerebral protection from subsequent ischemia within 24 h of initiation of the RPC stimulus and this protection in part may be mediated via a neurogenic pathway.