Effects Of Interauterine TCDD Exposure To Neurobehavioral Development And Spatial Memory And Learning In F1 Male SD Rat Offspring

2,3,7,8-Tetrachlorodibenzo-p-Dioxin(TCDD) is the most toxic congener of dioxin family, also a typical environmental endocrine disruptor. Dioxin and TCDD could pass the placental barrier, enter fetus through placental and breast milk, even at a very low level of exposure during geststion. Report from WHO pointed out in 2012, EEDs could influence early develop of exposure children, including cryptorchidism, hypospadias and early puberty, besides EEDs exposure could affect children nervous system development, leading to the defect of intelligence behavior and social-emotion. According to Developmental Origins of Health and Disease(DOHaD) Hypothesis, individual exposure to environmental insult during sensitive period, such as uteri and learly postnatal, could chang the programming or reprogramming the structure and function of orgns. Thses changes could induce to learning disorders and mental problems in later-life.ObjectiveThe purposes of our study was to investigate the influences of neurodevelopment and spatial memory and learning in F1 male offspring after gestational environmental endocrine disruptor TCDD exposure, and tried to explain the possible mechanism of all these changes.MethodsThe study assessed the nervous system development and spatial memory and learning in F1 male rats after TCDD uterine exposure.In our current study, animal model was established Sprague-Dawley rats were housed in plastic cage and were maintained at 25±2℃and 40-50% humidity, under standard 12/12 h light-dark cycle in a SPF biological laboratory. Food and water were available ad libidum. After acclimation, rats were mated overnight at a ratio of 1:1. The day sperm-positive vaginal plug observed were noted as gestation day 0(GD0). On gestational days 8-14(GD8-14), pregnant rats were given a consecutive daily dose of TCDD(200 or 800 ng/kg body weight/day, 5 ml/kg dosing preparation) or an equivalent volume of vehicle(i.e., DMSO and corn oil) in gavage. Pups were weaned until postnatal day 21. Male offspring were housed in the same condition until PND90.Early neurobehavioral developmental landmarks of male pups were designed at postnatal day 5(including Surface righting, Cliff avoidance and Negative geotaxis). Eye-opening was observes from postnatal day 10 until all male pups opened their eyes.On postnatal day 90, adult male rats were tested by Morris water maze to evaluate spatial memory and learning ability. Morris water maze designed according to the Nature Protocol. First 5 days were navigation trial, and then the sixth day was probe trial. All trials were videotaped, latency and cumulative distance(path length) to reach the platform was automatically recorded, as well as other behavioral information obtained during the acquisition training days. During the probe trial, the numbers of crossing over the previous platform, the time spent in each quadrant and the swim speed(cm/s) were also recorded.After Morris Water Maze test(3 days), all male rats were anesthetized by Chloral hydrate and were sacrificed. Blood samples were collected. We used ADVIA-Centaur XP to detect the level of Sex hormone(including testosterone and estradiol) and thyroid hormones(FT3, FT4, TT3, TT4 and TSH).Hippocampus was removed immediately and immersed in 4% Paraformaldehyde immediately for histological examinations. Nissl?s staining was designed to observe the morphology of hippocampus neuron and evaluate the number of neuron. Hippocampus astrocyte glial fibrillary acidic protein(GFAP) immunohistochemistry was used to evaluate the activity of astrocytes in hippocampus.Results1. Gestational TCDD exposure during gonadal sex determination could induce changes in early neurobehavioral develop in F1 male rats. Rats in 800ng/kg bw group performed higher motor activity and opened eyes earlier than control.2. Gestational TCDD exposure during gonadal sex determination induced F1 male rat spatial memory and learning defection when they turned to adult. Rats in 200 and 800ng/kg bw groups showed longer latency and longer path length to reach the hidden platform compared to the control group, In the probe test, the times of crossing over previous platform in the male rat of 800 ng/kg bw TCDD group was significantly reduced.3. Gestational TCDD exposure during gonadal sex determination induced F1 male rat serum hormones changes. Serum estradiol was decreased in 800ng/kg bw group compared to control, there were not significant decrease in serum testosterone and thyroid hormones(FT3, FT4, TT3, TT4).4. Gestational TCDD exposure during gonadal sex determination doesn?t affect the morphology and number of neuron in hippocampus CA1 subregion, while the activity of astrocytes in same region was significant reduce.ConclusionsGestational TCDD exposure during gonadal sex determination could lead to disadvantages in neurobehavioral development of F1 generation male rats. We observed promotion of early neurobehavioral development, while when F1 male rats turned to adult, their spatial memory and learning ability was damaged. Besides we found astrocytes activity in hippocampus CA1 region could related to this damage in adulthood. According to the serum estradio decreasing in TCDD treated groups, we could figure that, low level of estradio could not fully perform the protection of central nervous system. From our study, it?s highly possible that human gestational environmental endocrine disruptors exposure could induce neurobehavioral develop problems in offspring, especially of intelligence behavior and social-emotion. All these damages could last for whole life span. That remained us to pay more attention to the control of environmental endocrine disruptors, minimize the potential damages to human life.