Our study revealed that hyperglycemia increased expression of GRP78 and ATF6 in neurons at I/R 1 d, and that quercetin reversed the effect of hyperglycemia, indicating that hyperglycemia activated ERS and that the damage alleviating effect of quercetin in hyperglycemic ischemic animals is associated with inhibition of ERS. The gene discussed is HSPA5; the disease is Hyperglycemia.