ABSTRACT
Objective To evaluate the effect of ketamine on the expression of tryptophan hydroxylase 2 (TPH2) in the median raphe nuclei of mentally depressed mice.Methods Thirty-six healthy SPF male C57BL/6J mice,aged 8-12 weeks,weighing 20-26 g,were divided into 3 groups (n=12 each) using a random number table:control group (C group),depression group (D group) and depression plus ketamine group (D+K group).Mental depression was induced by forcing the animals to swim in a narrow cylinder from which they can not escape.Ketamine 15 mg/kg was intraperitoneally injected once a day for 7 consecutive days starting from 1 day after successful establishment of the model in group D+K.The equal volume of normal saline was given instead of ketamine in C and D groups_ Forced swimming test was performed again at 30 min after the last administration,and the immobility time was recorded.Open field test was also performed at 30 min after the last administration,and the total horizontal distance and the number of standing on the back legs were recorded.The mice were sacrificed after the end of the behavioral testing,and the hippocampi and median raphe nuclei were isolated.High-performance liquid chromatography-electrochemical detection assay was used to measure the content of 5-hydroxytryptamine (5-HT) in hippocampi.The expression of TPH2 protein and mRNA in the median raphe nuclei was detected using Western blot and real-time polymerase chain reaction,respectively.Results Compared with group C,the immobility time was significantly prolonged,the total horizontal distance was shortened,the number of standing on the back legs and content of 5-HT in hippocampi were deceased,and the expression of TPH2 protein and mRNA in the median raphe nuclei was down-regulated in group D,and the total horizontal distance was significantly shortened,the number of standing on the back legs was decreased (P＜0.05),and no significant change was found in the immobility time,content of 5-HT in hippocampi or expression of TPH2 protein and mRNA in the median raphe nuclei in group D +K (P＞0.05).Compared with group D,the immobility time was significantly shortened,the content of 5-HT in hippocampus was increased,the expression of TPH2 protein and mRNA in the median raphe nuclei was up-regulated (P＜0.05),and no significant change was found in the total horizontal distance or the number of standing on the back legs in group D+K (P＞0.05).Conclusion The mechanism by which ketamine produces anti-depressant effect may be related to up-regulation of TPH2 expression in the median raphe nuclei and increase in the synthesis of 5-HT in hippocampi of mice.
ABSTRACT
Alcohol abuse and cigarette smoking have been on the rise worldwide and it has been reported that alcohol and nicotine influence serotonergic neuronal activity in the dorsal raphe. Serotonin (5-hydroxytryptamine, 5-HT) has been implicated in the pathophysiology of various neuropsychiatric disorders. In the present study, the effects of alcohol and nicotine on the synthesis of 5-HT and the expression of tryptophan hydroxylase (TPH), the rate limiting enzyme of 5-HT synthesis, in the dorsal and median raphe of young rats were investigated via immunohistochemistry. The numbers of the 5-HT-positive and TPH-positive cells in raphe nuclei were reduced by alcohol and nicotine treatment, and these numbers were reduced more potently by co-administration of alcohol and nicotine. Based on the results, it can be suggested that the pathogenesis of alcohol- and nicotine-induced neuropsychological disorders involves alcohol- and nicotine-induced suppression of 5-HT synthesis and TPH expression in raphe, and that this may be of particular relevance in the consumption of alcohol and nicotine during adolescence.