Stress alters brain cell properties and then disturbs cognitive processes, such as learning and memory. In this study, we investigated the effect of postnatal treadmill exercise on hippocampal neurogenesis and spatial learning ability of rat pups following prenatal noise stress. The impact of exercise intensity (mild-intensity exercise vs heavy-intensity exercise) was also compared. The pregnant rats in the stress-applied group were exposed to a 95 dB supersonic machine sound for 1 h once a day from the 15th day after mating until delivery. After birth, the rat pups in the exercise groups were made to run on a treadmill for 30 min once a day for 7 consecutive days, starting 4 weeks after birth. The spatial learning ability was tested using radial-arm maze task and hippocampal neurogenesis was determined by 5-bromo-2′-deoxyuridine (BrdU) immunohistochemistry. The rat pups born from the stress-applied maternal rats spent more time for the seeking of water and showed higher number of error in the radial-arm maze task compared to the control group. These rat pups showed suppressed neurogenesis in the hippocampus. In contrast, the rat pups performed postnatal treadmill exercise saved time for seeking of water and showed lower number of error compared to the stress-applied group. Postnatal treadmill exercise also enhanced neurogenesis in the hippocampus. The mild-intensity exercise showed more potent impact compared to the heavy-intensity exercise. The present results reveal that postnatal treadmill exercise lessens prenatal stress-induced deterioration of brain function in offspring.
Stress is a biologically significant factor altering brain cell properties, and then disturbs cognitive processes, such as learning and memory, and consequently limits the quality of human life (
Hippocampus is the brain area implicated in memory acquisition and neuroendocrine regulation of stress hormones (
Exercise is known to enhance cell proliferation and/or neurogenesis in the hippocampal dentate gyrus (
In the present study, we investigated whether maternal stress during the late pregnancy exerts influence on hippocampal neurogenesis and spatial learning ability of offspring. And then, the effect of postnatal treadmill exercise on hippocampal neurogenesis and spatial learning ability of rat pups following prenatal noise stress were also investigated. In addition, the impact of exercise intensity (mild-intensity exercise vs heavy-intensity exercise) was also compared.
Male Sprague-Dawley rats (250±10 g, 12 weeks old, n=15) and female Sprague-Dawley rats (180±10 g, 8 weeks old, n=15) were used for this study. The experimental procedures were performed in accordance with the guidelines of the National Institutes of Health and the Korean Academy of Medical Sciences. The female rats were allowed to mate with the male rats for 1 day. After mating, the female rats were housed individually in a plastic home cage with a controlled temperature (20±2°C) and light-dark cycles consisting of 12 h light and 12 h darkness (lights on from 07:00 h to 19:00 h). Food and water were made available
Two weeks after mating, the pregnant rats were divided into two groups: the control group and the stress-applied group (n=6 in each group). From the 15th day after mating, the pregnant rats were subcutaneously injected with 100 mg/kg 5-bromo-2′-deoxyuridine (BrdU: Sigma Chemical Co., St. Louis, MO, USA), once a day at 30 min before the starting of experimental treatment until delivery. The pregnant rats in the stress-applied group were exposed to a 95 dB supersonic machine sound for 1 h once a day from the 15th day after mating until delivery, while the rats in the control group were left undisturbed. After birth, the offspring were left together with the respective maternal rats.
And then, the effects of intensity of postnatal treadmill exercise on hippocampal neurogenesis were investigated. The rat pups born from the control group were divided into three groups: the control group, the mild-intensity exercise group, and the heavy-intensity exercise group. The rat pups born from the stress-applied group were divided into three groups: the stress-applied group, the stress-applied and mild-intensity exercise group, and the stress-applied and heavy-intensity exercise group. The rat pups in the all groups were also subcutaneously injected with 50 mg/kg BrdU once a day at 30 min before the starting of treadmill running for 7 consecutive days.
The rat pups in the exercise groups were made to run on a treadmill for 30 min once a day for 7 consecutive days starting 4 weeks after birth, according to the previously described method (
The spatial learning ability was tested using radial-arm maze task, as the previously described method (
For brain tissue preparation, the animals were fully anesthetized with Zoletil 50® (10 mg/kg, i.p.; Vibac Laboratories, Carros, France), transcardially perfused with 50 mM phosphate-buffered saline (PBS), and then fixed with a freshly prepared solution consisting of 4% paraformaldehyde (PFA) in 100 mM phosphate buffer (PB, pH 7.4). The brains were then removed, postfixed in the same fixative overnight, and transferred into a 30% sucrose solution for cryoprotection. Coronal sections of 40 μm thickness were made using a freezing microtome (Leica, Nussloch, Germany).
For detection of newly generated cells in the hippocampus, BrdU incorporation was visualized
The area in the selected region of the hippocampus was measured using Image-Pro® Plus software (Media Cybernetics, Silver Spring, MD, USA). The number of BruU-positive cells in each area in the hippocampus was counted hemilaterally through a light microscope (Olympus, Tokyo, Japan). The data were expressed as the number of cells per mm2 of the area of the hippocampus. Statistical analysis was performed using t-test and one-way ANOVA followed by Duncan
The time taken to complete eight successful performances was 98.57±17.05 sec in the control group, 59.28±9.73 sec in the mild-intensity exercise group, 64.00±6.67 sec in the heavy-intensity exercise group, 294.33±54.41 sec in the stress-applied group, 76.22±8.53 sec in the stress-applied and mild-intensity exercise group, and 108.11±13.09 sec in the stress-applied and heavy-intensity exercise group.
The number of error made before eight successful performances was 6.57±1.70 in the control group, 2.42±0.76 in the mild-intensity exercise group, 4.42±0.91 in the heavy-intensity exercise group, 12.11±1.53 in the stress-applied group, 5.77±1.20 the stress-applied and mild-intensity exercise group, and 11.22±1.73 in the stress-applied and heavy-intensity exercise group.
In the present results, the rat pups born from the stress-applied maternal rats spent more time for the seeking of water and showed higher number of error in the radial-arm maze task compared to the control group (
The number of BrdU-positive cells the hippocampal CA1 region was 2,495.04±93.67/mm2 in the control group, 2,954.26±98.06/mm2 in the mild-intensity exercise group, 2,689.29±107.59/mm2 in the heavy-intensity exercise group, 2,200.28±132.77/mm2 in the stress-applied group, 2,617.42±72.86/mm2 in the stress-applied and mild-intensity exercise group, and 2,479.19±41.18/mm2 in the stress-applied and heavy-intensity exercise group.
The number of BrdU-positive cells in the hippocampal CA2 and CA3 regions was 1,187.69±28.84/mm2 in the control group, 1,644.55±121.70/mm2 the mild-intensity exercise group, 1,402.80 ±74.07/mm2 in the heavy-intensity exercise group, 1,096.42±60.82/mm2 in the stress-applied group, 1,303.50±76.68/mm2 in the stress-applied and mild-intensity exercise group, and 1,256.76±45.91/mm2 in the stress-applied and heavy-intensity exercise group.
In the present results, the rat pups born from the stress-applied maternal rats showed suppressed neurogenesis in the hippocampus compared to the control group (
Prenatal stress in rats induced lifespan reduction of neurogenesis in the hippocampal dentate gyrus and produced impairment in hippocampal-related spatial tasks (
In the present results, the rat pups born form the maternal rats exposed to the noise stress during pregnancy showed decrement in hippocampal neurogenesis. These rat pups also showed impairment of spatial learning ability.
Exercise has been recommended as one of the non-pharmacologic means for treating neuropsychiatric diseases (
In this study, we focused the effects of postnatal treadmill exercise of rat pups after receiving noise-induced stress during pregnancy. In the present results, postnatal treadmill exercise of rat pups born form the noise-exposed maternal rats during pregnancy showed increment in hippocampal neurogenesis. These rat pups also showed improved spatial learning ability in spite of noise exposure during pregnancy. In item of the exercise intensity, the mild-intensity exercise showed more potent impact compared to the heavy-intensity exercise. The present results reveal that post-natal treadmill exercise lessens prenatal stress-induced deterioration of brain function in offspring.
This work was supported by the National Research Foundation of Korea funded by the Korean Government (NRF-2010-327-G00123).
No potential conflict of interest relevant to this article was reported.
Photomicrographs of 5-bromo-2′-deoxyuridine (BrdU)-positive cells in the hippocampus. Black dots represent BrdU-positive cells. The scale bar represents 400 μm.