Background:Sevoflurane may have excitatory effect in CNS.Arc can be fostly expressed in hippocampus for the modulation of synaptic plasticity.ERK pathway revolves in learning and memory by mediating signals and modifications.This study arms at exploring their mechanism.Methods:SD rats were randomly assigned to three groups (sham.0.11% SEV and 0.3% SEV).Target dose of sevoflurane was given for 45rain and IA (0.4mA.2s) was followed alter inhalation.The memory retention was observed 24hs after.Westernblot of hippocampal tissue and PCR were pesformed after first IA.Results:0.11% SEV displayed an elevation of memory retention while 0.3% SEV descended.ARC mRNA levels showed no changes of ARC transcription level between groups.0.11% sevoflurane increased ARC protein in hippocampus.while 0.3% scvoflutane reversed it,Phosphorylated ERK was signiftcantly increased according to the increased concentration ofsevoflursne.Conclusion:ERK is down-regulated with hippocampal ARC expression in sevoflurane induced bidirectional regulation of memory.