Abstract: BACKGROUND: Eupatilin, a flavonoid active component derived from Artemisia sinensis, has been reported to relieve inflammation and improve neurological scores in rats with subarachnoid hemorrhage, but its role and mechanism in learning and memory remain unclear. 
OBJECTIVE: To investigate the effects of eupatilin on learning and memory abilities and P38 mitogen activated protein kinase (p38 MAPK)/signal transducer and activator of transcription-3 (STAT3) pathway proteins in rats with subarachnoid hemorrhage. 
METHODS: A total of 50 Sprague-Dawley rats were randomly divided into sham surgery group, model group, eupatilin group, hesperetin group, eupatilin+hesperetin group, with 10 rats in each group. Except for the sham surgery group, the rats in the other groups were used to construct a subarachnoid hemorrhage model through intravascular perforation. Two hours after successful modeling, the eupatilin group was injected with 10 mg/kg eupatilin via the tail vein, the hesperetin group was injected with 50 mg/kg hesperetin (p38 MAPK/STAT3 signaling pathway activator) via the tail vein, the eupatilin+hesperetin group was injected with 10 mg/kg eupatilin and 50 mg/kg hesperetin via the tail vein, and the sham surgery group and the model group were injected with 10 mL/kg saline via the tail vein. The drug treatment lasted for 24 hours. The neurologic deficit score and Morris water maze experiment were applied to detect the neurological function and learning and memory abilities of rats. Hematoxylin-eosin staining was performed to detect the histopathological changes of the hippocampus. TUNEL method was used to detect neuronal apoptosis. Immunohistochemical staining was conducted to detect the number of doublecortin-positive cells in hippocampal tissue. Western blot was applied to detect the expression of p38 MAPK/STAT3 protein in hippocampal tissue. 
RESULTS AND CONCLUSION: Compared with the sham surgery group, rats in the model group had lower neurological deficit scores, learning and memory abilities, and number of doublecortin-positive cells (P < 0.05), and higher neuronal apoptosis rate and protein expression of p-p38 MAPK/p38 MAPK and p-STAT3/STAT3 (P < 0.05). Compared with the model group, rats in the eupatilin group showed higher neurological deficit scores, learning and memory abilities, and number of doublecortin-positive cells (P < 0.05), and lower neuronal apoptosis rate and protein expression of p-p38 MAPK/p38 MAPK and p-STAT3/STAT3 (P < 0.05), while those in the nerolone group showed lower neurological deficit scores, learning and memory abilities, and number of doublecortin-positive cells (P < 0.05), and higher neuronal apoptosis rate and protein expression of p-p38 MAPK/p38 MAPK and p-STAT3/STAT3 (P < 0.05). Compared with the eupatilin group, rats in the eupatilin+hesperetin group had lower neurological deficit scores, learning memory abilities, and number of doublecortin-positive cells (P < 0.05), and higher neuronal apoptosis rate and protein expression of p-p38 MAPK/p38 MAPK and p-STAT3/STAT3 (P < 0.05). Hematoxylin-eosin staining showed that compared with the model group, the nerve cells were more neatly arranged in the eupatilin group, disorganized in the hesperetin group, and arranged in a similar way to the model group in the eupatilin+hesperetin group. To conclude, eupatilin may improve learning and memory abilities of rats with subarachnoid hemorrhage by inhibiting the p38 MAPK/STAT3 signaling pathway.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: eupatilin, P38 MAPK/STAT3 signaling pathway, subarachnoid hemorrhage, learning and memory abilities, neuronal death, engineered tissue construction