Background The early-life living environment plays an important role in the growth of offspring. Stressful events during pregnancy can induce changes in maternal intrauterine environment, which in turn affects the growth and development of offspring. Insulin like growth factor-Ⅱ (IGF-Ⅱ) and nuclear factor-κB (NF-κB) are mainly distributed in the areas related to cognition and emotional memory in the brain, they work together with monoamine neurotransmitters norepinephrine (NE) and dopamine (DA) to regulate the attention and response ability of the body. Enriched environment can improve learning and memory ability while promoting nerve regeneration through neurogenesis, synapsis, cerebrovascular regeneration and other neural remodeling effects.
Objective This experiment is designed to investigate the effects of enriched environmental intervention on the expressions of hippocampal synapse-associated proteins such as IGF-Ⅱand NF-κB in offspring of rats with chronic stress during pregnancy.
Methods Twenty female Wistar rats were randomly divided into a model group and a control group of 10 rats each; 15 male Wistar rats were randomly divided into a model group of 10 rats and a control group of 5 rats. The female rats of the model group received chronic unpredictable mild stress (CUMS) for 21 d, and were caged at a 1:1 female-to-male ratio on the 3rd day of the CUMS protocol. The female rats of the control group were reared in normal environment and caged at a 2:1 ratio. Blood samples were collected from the iliac vein of the female rats 1 day before and 1, 7, and 14 days after the CUMS protocol, and measured for plasma cortisol content by radioimmunoassay to calculate corticosterone concentration. The offspring rats were weaned on postnatal day 21 (PND21). The control offspring rats were randomly divided into a control offspring group and a control + enriched environment offspring group. The model offspring rats were divided into a model offspring group and a model + enriched environment offspring group, with 16 pups in each group. The offspring rats of two enriched environment groups were exposed to enriched environment for 6 h (13:00-19:00) every day, and the intervention period was 30 d. The other offspring rats were raised in normal environment. The offspring body weight was weighed on PND50, and behavioral parameters were measured, including horizontal movement score and vertical movement score, using a self-designed open box. Then the offspring rats were sacrificed and hippocampal tissue samples were collected. The levels of monoamine neurotransmitters norepinephrine (NE) and dopamine (DA) in hippocampus of the offspring rats were detected by ELISA. The relative expression levels of IGF-Ⅱ and NF-κB mRNA and protein in hippocampus of the offspring rats were determined by real-time quantitative PCR and Western blotting, respectively.
Results The plasma corticosterone concentrations of the female rats in the model group on the 7th and 14th days of stress(348.50±13.24) and (258.38±22.77) μg·L-1 were higher than those of the female rats in the control group(224.00±39.84) and (218.78±16.68) μg·L-1 (P < 0.05), suggesting that the female rats in the model group were stressed during pregnancy. After the enriched environment intervention, the body weights of the offspring rats in the model + enriched environment group and the control + enriched environment group on PND50(191.70±18.31) and (208.80±21.40) g were higher than those of the offspring rats in the model group and the control group(175.70±8.12) and (190.40±16.47) g (P < 0.05). The scores of horizontal movement and vertical movement of the offspring rats in the model + enriched environment group(46.10±9.26) and (23.50±7.99) were higher than the scores of the offspring rats in the model group(24.40±8.30) and (16.30±4.42) (P < 0.05). The vertical movement score of the offspring rats in the control + enriched environment group (27.20±9.94) was higher than that of the offspring rats in the control group (21.70±6.83) (P < 0.05). The levels of NE and DA of the model + enriched environment offspring group(1.42±0.65) and (2.85±0.75) μg·L-1 were higher than those of the model offspring group(0.89±0.26) and (1.94±0.64) μg·L-1 (P < 0.05). Compared with the model offspring rats(0.50±0.19) and (0.96±0.30), the relative expression levels of IGF-Ⅱ and NF-κB mRNA in hippocampus of the model + enriched environment offspring rats were increased(1.11±0.53) and (1.55±0.69) (P < 0.05). The relative expression levels of IGF-Ⅱ and NF-κB proteins in hippocampus of the model + enriched environment offspring rats(0.83±0.10) and (0.67±0.27) were higher than those of the model offspring rats(0.40±0.07) and (0.30±0.16) (P < 0.05); the relative expression levels of IGF-Ⅱand NF-κB proteins in hippocampus of the control + enriched environment offspring rats(1.41±0.11) and (0.75±0.30) were higher than those of the control offspring rats(0.76±0.07) and (0.59±0.07) (P < 0.05).
Conclusion Enriched environment can promote the weight gain and exercise capacity of the offspring of chronically stressed rats during pregnancy, and can increase the expressions of monoamine neurons NE and DA and synaptic related proteins NF-κB and IGF-Ⅱ in offspring hippocampus.
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