Alterations Of Brain-derived Neurotrophic Factor, Tyrosine Related Receptor Kinase B And CAMP Response Element Binding Protein In The Hippocampus Of Gulf War Syndrome Rats

Objective: After the end of Gulf War, some soldiers of the U.S. military who participated in the Gulf War in the early nineties of last century appeared perseverative health problems which was difficult to deal with and also difficult to confirm the diagnosis with current medical and psychiatric theory, therefore it was termed Gulf War syndrome (GWS) or Gulf War illness (GWI). According to the definition given by U.S CDC in 2000, GWS symptoms were divided into three groups, namely non-exercise fatigue, emotional or cognitive disorders (anxiety, depression, emotional volatility, lack of concentration, sleep disturbance), skeletal muscle system abnormalities (two or more joints, muscle pain). The Patient who has at least one of the three symptoms can be diagnosed as GWS. The causes of GWS were still unknown, include depleted uranium weapons, pyridostigmine bromide (PB), pesticides (DEET), severe psychological stress and trauma, the unique Kuwait oil well fire smoke, vaccination, gastrointestinal and respiratory infections disease and the others. Base on the epidemiological studies of the Gulf War, it is agreed that the use of PB (to prevent the nerve gas) and DEET had significant correlation with the incidence of GWS. MRI studies showed that hippocampus volumes of the patients with GWS were significantly smaller than normal subjects. Brain-derived neurotrophic factor (BDNF) is the most abundant brain neurotrophic factor in brain, mainly detected in hippocampal neurons. Protein tyrosine kinase B receptor (TrkB) is the major high affinity receptor of BDNF. The expression of BDNF is directly regulated by the cAMP response element binding protein (CREB). In the chronic stress, BDNF is closely related with the damage of hippocampus. The purpose of this study is to establish the rat models of the Gulf War syndrom and chronic restraint stress, to observe the changes of the expressions of BDNF and its receptor TrkB as well as transcription factor CREB in hippocampal CA1 area, and to explore whether hippocampal damage in GWS relate to the change in the expression of BDNF.Methods: We established the chronic stress rat model by chronic restrictive stress and the Gulf War syndrome rat model by reference of Abdel-Rahman et al study. The animals were divided into three groups: 1. Control group: drinking water, subcutaneous injection of 70% ethanol; 2. Chronic restraint stress group: drinking water, subcutaneous injection of 70% ethanol, limiting stress 20min / d; and 3. Gulf War syndrome model groups: drinking PB (1.3mg / kg / d) with water, subcutaneous injection of DEET (40mg/kg/d) and 70% ethanol, limiting stress 20min /d. The experiments lasted 28 days. The weights of the animals in all groups were measured and recorded at 0 days, 14 days, 28 days. After the experiment, a half of experimental animals of each group was prepared to paraffin section for SABC immunohistochemical staining to examine the expressions of BDNF, TrkB, phaspho-CREB (pCREB) in hippocampus; another half of the animals were used for Western blot analysis.Results: 1. The weight of the rats increased in all groups, 42.65% in control group, 42.30% in chronic restraint stress group , 37.05% in GWS model group. Compared with control group, the weight gain of rats in model group and restrictive stress group had no significant statistical difference (P>0.05). 2. Immunohistochemical results: The average optical density of BDNF in the restraint stress group was lower than that of the control group (P <0.05). Compared with the control group and the chronic restraint stress group, the average optical density of BDNF in GWS model group was significantly decreased (P <0.05). The above immunohistochemical results were further demonstrated by Western blot analysis.Similar results were detected as to the changes of TrkB and pCREB in each group.Conclusion: 1. Weight gain was unaffected by chronic restrictive stress or PB / DEET treatment; 2. Chronic restrictive stress treatment could decrease the expressions of BDNF, TrkB, and pCREB in hippocampus of rats, indicating that BDNF plays an important role in the pathological process of hippocampus under chronic restrictive stress. 3. The expressions of BDNF, TrkB, and pCREB decreased in hippocampus of GWS rats, even significantly lower than these of chronic stress-treated rats. It revealed that PB and DEET might have effect on hippocampus by reducing the expressions of BDNF, TrkB, and CREB ,that might make GWS patients have corresponding clinical symptoms.