The Effect of Physical Activity on Serum Oxytocin Levels and Depression During Pregnancy and Postpartum in Female Mice

Mothers experience hormonal changes and mood disorders during pregnancy. Oxytocin plays a central role in the nervous system in both directions of the mother-infant relationship. In the mother's body, this hormone is normally present in the hormonal cycle and is released from the posterior pituitary gland, and also plays an important role during vaginal stimulation and delivery by acting on receptors (3). The onset of depressive symptoms in the first two weeks after delivery is directly related to a decrease in plasma oxytocin levels during pregnancy, which impairs the emotional adjustment of mother and baby (42). Since physical activity leads to stress in the body and improves blood circulation in the heart and blood vessels, which stimulates the posterior pituitary gland to secrete oxytocin; Exercise can increase oxytocin levels in pregnant women (5). There are drug restrictions for mothers in the treatment of depression during pregnancy and postpartum. Postpartum depression is a condition characterized by persistent experiences of sadness or decreased ability to experience pleasure, irritability, low self-esteem, and overt anxiety (2). Depression in pregnant women is a threat not only to the health of the mother, but also to the health of the baby. Depressive disorders may affect the baby from the embryonic stage, and may also affect the delivery process and the mother-baby relationship in later years. It is important to note that even regular walks that are low-intensity exercise during pregnancy can significantly reduce depressive symptoms in pregnant women (17). Physical activity can also have a positive effect on depressive disorders. After exercise, endorphin levels rise, which is responsible for a more positive and happy mind. While depression reduces the levels of neurotransmitters such as serotonin, norepinephrine or dopamine, their concentration increases with physical activity (8). There is a sudden increase in body size and weight during pregnancy, while physical activity prevents overweight or obesity (11). Therefore, today, exercise for women during pregnancy and after is emphasized by experts (6). According to the American Congress of Midwifery, pregnant women can exercise for 30 minutes or more a day with moderate intensity during pregnancy, but not every day of the week, if there is no ban. High-intensity exercise is not recommended during pregnancy due to insufficient studies on the level of intensity (1). However, it should be borne in mind that for the safety of pregnant women and children, all activities should be performed in consultation with a gynecologist. If the type of physical activity is carefully selected and whether it is done under supervision or without supervision (optional exercise), statistically significant results will be achieved in reducing depressive symptoms. The aim of this study was to evaluate the effect of exercise on serum oxytocin levels and depression during pregnancy and postpartum in female mice.

This study is an experimental study that was performed in the laboratory on mice and is applied in terms of purpose. Sixty healthy female NMRI mice with an approximate age of 80-90 days and weighing 22-25 g were prepared from Pasteur Institute of Iran and kept in light conditions for 12 hours of light and 12 hours of darkness at a temperature of 23 ± 1 °C. Adequate food was provided to them. NMRI mice, after two weeks of adaptation,were given one male for each female to mate, and they were placed in a cage several times to obtain the required number of pregnant mice. Then, the next morning, the vaginal plaque was checked as a pregnancy indicator. Thus, 40 female mice became pregnant and these mice, in which vaginal plaque was seen, were considered as the first day of pregnancy and the animals were transferred to separate cages. Inside the cage of each pregnant animal were two rotating wheels for exercise. By the end of the study, the rotating wheels were inside the animal cage. In this study, animals were divided into four groups to measure depression and oxytocin levels during pregnancy and postpartum. There were 10 NMRI mice in each group. Group 1: Active female mice were tested for behavioral and hormonal disorders during pregnancy. Group 2: Active female mice underwent behavioral and hormonal tests in the post-pregnancy period. Group 3: Active female mice were tested for behavioral and hormonal measures during pregnancy. Group 4: Active female mice underwent behavioral and hormonal tests in the post-pregnancy period. Active group exercise was optional. Exercise and non-exercise rats in the pregnant group on the 18th day of gestation and exercise and non-exercise rats in the postpartum group were evaluated on the 7th day postpartum. First, each mouse was exposed to another unfamiliar mouse and gently placed in the opposite corners of a 20 × 80 × 80 cm square box and examined for 7 minutes. The amount of time animals spend interacting with each other is considered an indicator of depressive behavior. After behavioral assessments, deep anesthesia was performed with ketamine (50 mg / kg) and xylazine (5 mg / kg). The animal's breast was then dissected and blood was drawn from the heart. The vials containing blood were placed on an ice pack for 30 minutes, then centrifuged at serum at 2000 RPM for 15 minutes and stored at -20 ° C. Serum oxytocin levels were measured based on the method in the RayBiotech Co. kit using ELISA technique. Shapiro-Wilk test was used to evaluate the normality of data distribution. Levin test was used to evaluate the homogeneity and homogeneity of variance of dependent variable between different samples. One-way analysis of variance with Tukey post hoc test was used to evaluate the differences between the groups. All statistical tests were performed at the significance level of P <0.05 by SPSS software version 22.

The results showed that the mean changes of oxytocin during pregnancy and postpartum were significantly different between active and inactive groups. The results of the depression test showed that the duration of visit of mice between the active and inactive groups during pregnancy was not significantly different, but in the postpartum period in the active group, a significant change was observed .The test was based on social interaction, meaning that the longer the interaction, the better, and shows that depression is improving.

Based on this study, it can be concluded that physical activity reduces the symptoms of depression during pregnancy and can be a safe preventive treatment. Physically active women have a lower risk of depression than inactive women. Physical activity also indirectly stimulates the secretion of oxytocin, which can reduce the symptoms of depression in the postpartum period. On the other hand, oxytocin secretion during pregnancy also has an advantage. It should also be noted that the introduction of physical activity during or before pregnancy does not always protect a pregnant woman from developing depression or does not affect its course during pregnancy. This indicates the existence of multifactorial dependence, where physical activity is only one component. It is difficult to determine the release of central oxytocin in humans, and the exact mechanism of the link between oxytocin and depression has not yet been determined, and these studies are mostly derived from animal studies. Overall, oxytocin is involved in the cause of depressive symptoms in the postpartum period and more research should be done on the neurological and endocrine aspects.