Chronic Administration of Thymoquinone Enhances Adult Hippocampal Neurogenesis and Improves Memory in Rats Via Regulating the BDNF Signaling Pathway

Thymoquinone is a pharmacologically active component of Nigella sativa Linn. seeds. Despite the diverse neuropharmacological attributes of TQ, limited reports related to adult neurogenesis and memory research are available. In this study, we investigated the effects of TQ on the proliferation and neural differentiation of cultured neural stem/progenitor cells (NSCs/NPCs). We also investigated the effect of TQ chronic administration on neurogenesis and memory in adult rats. Under proliferation conditions, TQ (0.05-0.3 mu M) significantly increased NSCs/NPCs viability, neurosphere diameter, and cell count. TQ treatment under differentiation conditions increased the proportion of cells positive for Tuj1 (a neuronal marker). Furthermore, chronic oral administration of TQ (25 mg/kg/day for 12 weeks) to adult rats increased the number of bromodeoxyuridine (BrdU)-immunopositive cells double-stained with a mature neuronal marker, neuronal nuclei (NeuN), and a proliferation marker, doublecortin (Dcx), in the dentate gyrus of the hippocampus. TQ-administered rats showed a profound beneficial effect on avoidance-related learning ability, associated with an increase in the hippocampal mRNA and protein levels of brain-derived neurotrophic factor (BDNF), as measured by both real-time PCR and ELISA. Western blot analysis revealed that TQ stimulates the phosphorylation of cAMP-response element-binding protein (CREB), the upstream signaling molecule in the BDNF pathway. Furthermore, chronic administration of TQ decreased lipid peroxide and reactive oxygen species levels in the hippocampus. Taken together, our results suggest that TQ plays a role in memory improvement in adult rats and that the CREB/BDNF signaling pathways are involved in mediating the actions of TQ in hippocampal neurogenesis.

百里醌是黑种草种子的一种药理活性成分。尽管百里醌具有多种神经药理学特性，但有关成年神经发生和记忆研究的报道有限。在本研究中，我们探讨了百里醌对培养的神经干细胞/祖细胞（NSCs/NPCs）增殖和神经分化的影响。我们还研究了百里醌长期给药对成年大鼠神经发生和记忆的影响。在增殖条件下，百里醌（0.05 - 0.3 μM）显著提高了神经干细胞/祖细胞的活力、神经球直径和细胞数量。在分化条件下，百里醌处理增加了Tuj1（一种神经元标志物）阳性细胞的比例。此外，对成年大鼠长期口服百里醌（25 mg/kg/天，持续12周）增加了海马齿状回中溴脱氧尿苷（BrdU）免疫阳性细胞的数量，这些细胞同时被成熟神经元标志物神经元核（NeuN）和增殖标志物双皮质素（Dcx）双重染色。给予百里醌的大鼠在回避相关学习能力方面表现出显著的有益作用，同时通过实时定量聚合酶链反应（real - time PCR）和酶联免疫吸附测定（ELISA）检测发现，海马脑源性神经营养因子（BDNF）的mRNA和蛋白质水平升高。蛋白质印迹分析显示，百里醌刺激环磷腺苷效应元件结合蛋白（CREB）的磷酸化，CREB是BDNF通路中的上游信号分子。此外，百里醌长期给药降低了海马中的脂质过氧化物和活性氧水平。综上所述，我们的研究结果表明，百里醌在成年大鼠的记忆改善中发挥作用，并且CREB/BDNF信号通路参与介导百里醌在海马神经发生中的作用。