| Summary: | 碩士 === 國立陽明大學 === 解剖學及細胞生物學研究所 === 102 === Abstract
Background: Scopolamine, an acetylcholine muscarinic receptor antagonist, has long been regarded as a memory blocking agent. However, it was serendipitously discovered to produce rapid anti-depression effect in 2006. The mechanism underlying the therapeutic effect response is yet unknown. We used behavioral methods to assess mouse emotions, wireless electronic devices to record mouse’s autonomic nervous responses and sleep pattern, and molecular methods to examine the mammalian target of rapamycin complex 1 (mTORC1) signaling in mouse brain under the influence of scopolamine.
Materials and methods: 8-10 week-old male C57BL/6J Narl mice were used for experiments. We used stress-induced helplessness to model depression. Mice with a <60% success rate in the escape test after stress was regarded as helpless. Helpless mice were randomly assigned to receive scopolamine (1 mg/kg), methyl-scopolamine (1 mg/kg) or vehicle group. Thirty minutes after drug administration, the mice were re-evaluated in the escape test. The forced swim test (FST) was also used to evaluate scopolamine’s antidepressant effect. We implanted wireless electronic device on mouse skulls to record ECG, EEG and EMG. A week after operation, the mice were given scopolamine or vehicle and the electronic device was switched on to record the EEG, EMG and ECG signals for five hours. The EEG and EMG were used to determine sleep patterns and the ECG was analyzed to get heart rate variability. Another set of mice without electronic device were sacrificed for regional brain analysis after scopolamine/vehicle administration. Akt, phosphorylated Akt (ser473) (p-Akt), mTORC1 and phosphorylated mTORC1 (ser2448) (p-mTORC1) in the hippocampus and prefrontal cortex (PFC) were detected with western blots. The immunoreactive bands were quantified by densitometry using the Image J software. SPSS software was used for statistical analysis.
Results: The mice received scopolamine showed less immobility time than controls in the FST (p<0.001). In the stress-induced helplessness model, scopolamine increased successful escape rate and reduced escape time (p<0.01, p<0.05, respectively), but the effects were not observed with methyl-scopolamine. The mice treated with scopolamine displayed longer quiet sleep (deep sleep) (p<0.05), a higher ratio of delta wave (slow wave, indicating deep sleep) (p<0.001), and less paradoxical sleep (light sleep) (p<0.01) than control mice. Stress reduced p-Akt/Akt (p<0.001) and p-mTORC1/mTORC1 (p<0.01), while scopolamine increased p-Akt/Akt (p<0.01) and p-mTORC1/mTORC1 (p<0.01) in the hippocampus. The effects were not observed in the PFC.
Conclusion: Scopolamine exerts its anticholinergic effect through the brain rather than the peripheral nervous system to improve sleep and depression-like helplessness in mice. The molecular mechanism of scopolamine’s effects on emotional behaviors is possibly due to activation of the mTORC1 signaling pathway in the hippocampus.
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