Abstract: ObjectiveTo explore the potential behavioral alterations in the Morris water maze test and the changes of neural nitric oxide synthase(nNOS)expression in the brain of offspring rats born by cesarean section.MethodsThe pregnant rats were randomly allocated into vaginal delivery and cesarean section groups.Fetuses were delivered by cesarean section on day 21 of the gestation.Morris water maze tests were performed on postnatal day 30 and 115.Then the offspring rats were sacrificed and their brain tissues were collected on postnatal day 7,30 and 115.Using immunohistochemical staining,the expressions of nNOS in the cortex of frontal lobe,hippocampus and corpora striatum were detected.ResultsMorris water maze results showed that the escape latency of the offspring rats,on postnatal day 115,in vaginal delivery group was significantly shorter than that of cesarean group(19.36±10.51 s vs 30.51±14.11 s,P<0.05).Immunohistochemical staining manifested that the density of nNOS positive cells in frontal cortex of 30-day-old offspring rats in cesarean section group(3.60±2.07)was higher than that of vaginal delivery group(1.20±0.45)(P<0.05).The density of nNOS positive cells in the hippocampus in vaginal delivery group was significantly fewer than that of cesarean section group(1.20±0.45 vs 5.80±1.79,P<0.001).The density of nNOS positive cells within the corpora striatum in vaginal delivery group(0±0) was significantly lower than that of cesarean section group(21.4±9.13)(P<0.001).In the offspring rats of 115-day-old, the density of nNOS positive cells in the hippocampus of vaginal delivery group(2.00±0.71)were fewer than that of cesarean group(3.80±1.48)(P<0.05).ConclusionThe upregulated expression of nNOS in the cortex,corpora striatum of offspring rats born by cesarean section might revert to normal in adulthood.The abnormal nNOS expression in hippocampus will remain even in adulthood and results in the abnormality of behavior cognitive ability.The results indicate that cesarean delivery could impact hippocampus region persistently and impair the spatial memory and learning ability related to hippocampus in rats.