Supplemental Effect of Garlic and Stevia Extract along with Endurance Activity on Serotonin and Serotonin-Receptor Gene Expression in the Brain Tissue of Male Wistar Rats Obesity

Several studies have reported that obesity causes vascular disorders in all tissues such as the heart and even the central nervous system along with disorders in the function of the hypothalamus, in such a way that these disorders in the nervous system, especially in the hypothalamus as the center of homeostasis and control of satiety and hunger can cause a significant increase in weight at different ages and even in children. Recent studies have led researchers to the etiology of this global epidemic and have drawn their attention to the influence of genetics, environmental factors, social and behavioral factors. Appetite is a physiological response to eating food, and behavioral signals and energy fluctuations throughout the day regulate the appetite in the central nervous system. Among these, the monoamine neurotransmitter serotonin can cause the development and evolution of some behaviors related to appetite through the regulation of the interval between two meals and the role of this neurotransmitter in inducing satiety. On the other hand, some studies have shown that moderate and intense sports activity and even intense intermittent exercise led to an increase in serotonin levels, which can have an effect on the caloric intake of obese women. In addition, recently, the attention of sports science researchers has been drawn to the use of medicinal plants effective in fat metabolism. Among medicinal herbs, there has been a recent increase in interest in naturally sweet herbs such as stevia and garlic. The purpose of this research was to investigate the effect of endurance training with garlic and stevia supplementation on serotonin gene expression and serotonin receptor in the brain tissue of obese Wistar rats.

35 obese male Wistar rats fed with a high-fat diet (24 grams of fat, 24 grams of protein and 41 grams of carbohydrates per 100 grams) were divided into seven groups, including: 1) Sham. 2) stevia supplement, 3) garlic supplement, 4) endurance exercise, 5) stevia supplement+endurance exercise, 6) garlic supplement+endurance exercise, and 7) healthy control. The training groups performed incremental endurance training for 15-50 minutes at a speed of 15-25 meters per minute, five sessions per week for eight weeks. Garlic and stevia supplements were added to the diet of the supplemented groups at a dose of 250 mg/kg. 48 hours after the last training session and in a state of 12 hours of fasting, the rats were anesthetized with ketamine (80 mg/kg) and xylosin (15 mg/kg) in a ratio of 3 to 1. Further, after ensuring complete anesthesia and painlessness, rats were perfused with 10 cc of 9% sodium chloride to drain the brain tissue from the blood. In order to extract the brain tissue, first the rats were completely restrained and after cutting the upper part of the skull, the brain tissue was carefully separated, and after weighing and washing, they were placed in special tissue preservation cryotypes and immediately cooled to -80 were transferred. The qReal Time PCR method was used to measure the gene expression levels of the variables in the brain tissue. One-way ANOVA with Tukey’s post hoc test was used for the data analysis. All statistical methods were performed using SPSS version 26 software at a significance level of P<0.05.

Regarding serotonin, the results showed that there was no significant difference in serotonin gene expression level between the healthy control group and the sham group (P = 0.903). Also, there was no significant difference between the sham group with stevia (P = 0.856), garlic (P = 0.994), endurance training+stevia (P = 0.303) and endurance training+garlic (P = 0.094). However, the results showed that the serotonin gene expression level of the endurance exercise group was significantly higher than that of the sham group (P = 0.000). Another important result is that there was no significant difference between the stevia and garlic groups (P = 0.996). However, adding endurance training to stevia had a significant effect on serotonin gene expression, so that the level of serotonin gene expression in the stevia+exercise group was significantly higher than the stevia group (P = 0.022). Also, adding endurance training to garlic caused the level of serotonin gene expression in the garlic+exercise group to be significantly higher than the stevia (P = 0.005) and garlic (P = 0.021) groups. Finally, the expression level of serotonin gene in the exercise group was significantly higher than all groups (P < 0.05).Regarding the serotonin receptor, the results showed that the expression level of the serotonin receptor gene in the healthy control group is significantly higher than the sham group (P = 0.003). Also, the level of serotonin receptor gene expression in stevia (P = 0.000), exercise (P = 0.000), exercise+garlic (P = 0.002) groups was significantly higher than the sham group. From other important results, it can be stated that the level of serotonin receptor gene expression in the stevia group was significantly higher than that of the garlic group (P = 0.000). Adding endurance exercise to stevia caused the serotonin receptor gene expression level to be significantly lower than the stevia group (P = 0.000). But, adding endurance exercise to garlic caused the serotonin receptor gene expression level to be significantly higher than the garlic group (P = 0.006). Finally, the expression level of the serotonin receptor gene in the exercise group was significantly higher than all groups (P < 0.05).

It seems that aerobic exercise with stevia supplement with AMPK activation mechanism activates hormone-sensitive lipase, improves fat and sugar metabolism and increases the expression of metabolic proteins in the hypothalamus. Therefore, it seems that consumption of stevia and aerobic exercise have synergistic effects in modulating and increasing serotonin in the brain tissue of desert rats exposed to high-fat food. Therefore, it can be concluded that endurance training with stevia supplementation synergistically affects the appetite control protein. However, more studies are needed on the changes in serotonin and serotonin receptor levels following the exercise and supplements used in this study.