Objective To investigate the effect of subclinical hypothyroidism during pregnancy on hippocampus insulin-like growth factor Ⅰ (IGF-Ⅰ) signaling pathway in rat offspring.Methods A total of 60 female Wistar rats were evenly divided into control(CON),subclinical hypothyroidism(SCH),and clinical hypothyroidism (CH) groups.The hippocampus of progenies were collected on the postnatal day 3,postnatal day 7 to measure protein kinase B (Akt) and phosphorylated-Akt (p-Akt) by Western blot,IGF-Ⅰ and insulin-like growth factor Ⅰ receptor (IGF-Ⅰ R) by Elisa.Morris water maze and field excitatory postsynaptic potential long-term potentiation were measured at the postnatal 40 day.Results Western blot and Elisa revealed that levels of IGF-Ⅰ,IGF-Ⅰ R,and p-Akt of pups from SCH group were lower than that of CON group and were higher than CH group on day 3 (P ＜ 0.05).On day 7,the levels of IGF-Ⅰ,IGF Ⅰ R,and p-Akt of pups from SCH group were lower than CON group (P＜ 0.05),but no difference was observed in p-Akt and IGF-Ⅰ R level between SCH group and CH group (P ＞ 0.05).Latencies of all groups had shortened in Morris water maze test with increasing of training trials.The slope of field excitatory postsynaptic potenial was increased in all groups after Theta burst stimulation.The amplification percentage of slope of field excitatory postsynaptic potenial in SCH group's was lower than control group's but was higher than CH group's(all P values＜0.05).Conclusions Maternal subclinical hypothyroidism impairs long-term potentiation induction in hippocampus of rat might be associated with the levels of IGF-Ⅰ,IGF-Ⅰ R,and p-Akt.