| Objective: Stress is the body’ systemic and nonspecific adaptive reaction in the act of a variety of internal and external environmental factors and the social and psychological factors, also known as stress reaction, the stimulus is called the stress factor. Along with the society’s development and progress, there are more and more stress factors, as well as getting more and more attention. Virtually every aspect of our body and brain can be influenced by stress. Chronic stress is associated with impaired cognition, as well as causing neuroendocrine system and brain proteins alterations. However, the precise mechanism of stress-associated cognitive deficits has not been clear yet. And the effective preventive and therapeutic means is still to be determined in clinic. Stress-associated cognitive deficits were observed together with reduced synaptic proteins and neurotrophic factor expression. Brain derived neurotrophic factor(BDNF), as a member of the neurotrophin family, plays an important role in memory and synaptic plasticity. It has been shown that, neurons in the hippocampus respond to repeated stress by showing atrophy and a down-regulation BDNF expression that is associated with memory impairment [1]. These data suggest that BDNF may be potentially participates in the molecular mechanism of stress-associated cognitive deficits. How to prevent the hippocampus neuron damage and the decline of BDNF caused by chronic stress plays a role in the prevention and treatment of stress-associated cognitive deficits. Now more recognized animal model of chronic stress mainly include: chronic restraint stress model, chronic unpredictable mild stress model, communication model, social failure stress animal model and the empty bottle stress model, etc.[2-5] Among them, the chronic restraint stress model is relatively simple and easy to operate, and is one of the most popular stress model. More than a large number of clinical studies have confirmed that salvianolic acids exerts a variety of pharmacological effects, including improving microcirculation, anti-inflammatory, antioxidant, eliminating free radicals and neuroprotective effects. This study intends to establish a chronic restraint stress model to explore the potential neuroprotective effects of salvianolic acids against restraint stress-induced cognitive deficits and the mechanisms and the change of the expression of BDNF in the hippocampus. Methods: 3 months healthy male Kunming mice were used in the chronic restraint stress model. The mice were randomly divided into the following three groups(n = 14):(1) The control group(control): The mice without stress treatment and with daily intraperitoneal injection of saline(10ml/kg).(2) The chronic restraint stress group(stress): The mice with daily intraperitoneal injection of saline(10ml/kg), and restraint for 8 h(9:00-17:00).(3) The chronic restraint stress plus salvianolic acids group(stress+sal): The mice with daily intraperitoneal injection of salvonolic acids(10ml/kg), and restraint for 8 h(9:00-17:00). Mice in each group were bred under the same conditions with food and water adlibitum for 14 days. At the first, seventh and fourteenth day, we weighed them. Then, their learning and memory capacity were tested by novel object recognition test(NORT). After the behavioral tests, the mice were sacrificed by decapitation and their brains were collected. And then, observed the neuropathological changes of hippocampal neurons in each group by HE-stainning and detected the hippocampus BDNF mRNA and protein expression by real-time PCR and immunohistochemical method. Result: 1 Changes of body weight At the first, 7th and 14 th day, we weighed the mice. The increment of body weight(g) =14th day body weight(g) – first day body weight(g). The results showed: at the first day, the control group body weight was 40.50 ± 2.66. Compared with control group, the stress group body weight(39.78±2.71) and the stress+sal group body weight(38.93±1.50) were no significant difference. At the 7th day, the control group body weight was 47.03±2.40.Compared with control group, the stress group body weight(42.30 ±2.93) and stress+sal group body weight(40.64 ± 3.33) were significantly decreased(P < 0.01). At the 14 th day, the control group body weight was 48.53±3.01. Compared with control group, the stress group body weight(43.61± 3.92) and stress+sal group body weight(42.69±2.35) were significantly decreased(P < 17.76±2.76.The stressed rats spent less time(11.86±2.42) exploring the novel objects, compared with that of the control group(P < 0.05) and stress+sal The results showed that chronic stress made the expression of BDNF mRNA declined significantly, and salvonolic acids can improve the expression of BDNF gene. 5 Changes of the BDNF protein in hippocampus We used immunohistochemical method to detect the BDNF protein expression in hippocampus and counted the number of immunopositive cells of BDNF in each group. The number of immunopositive cells of BDNF in control group was 36.08±0.7 and that of the stress+sal group was 34.19±0.6. The number of immunopositive cells of BDNF in stress group(33.49±0.98) was significantly lower than the control group(P < 0.05) and stress+sal group(P < 0.05). The above results showed that chronic stress made the expression of BDNF protein declined significantly, and salvonolic acids can improve the expression of BDNF protein. Conclusion: Salvonolic acids can significantly improve cognitive dysfunction caused by chronic stresses; its possible mechanism is the improvement of BDNF expression in hippocampus. |
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