The aim of the present study was to investigate the effects and possible mechanism of tetramethylpyrazine(TMP)on morphine-induced microglia activation and tolerance. The antinociception and morphine tolerance were assessed in mice using hot-water tail flick test. IBA-1(ionized calcium binding adapter molecule 1), the marker of microglia, was detected by immumofluorescence method. The expression of p-p38 MAPK and total p38 MAPK(mitogen-activated protein kinase, MAPK)was analyzed by Western blot; real-time polymerase chain reaction(RT-PCR)was used to detect the expression level of tumor necrosis factor-α(TNF-α)and interleukin-1β(IL-1β). Results showed that TMP(15, 30, 60 mg/kg, ip)inhibited morphine-induced up-regulation of IBA-1, p-p38, TNF-α and IL-1β in a dose-dependent manner, yet with no effect on the expression of total p38 MAPK. In conclusion, TMP significantly inhibited the activation of microglia evoked by morphine via p38 MAPK signaling pathway, thus attenuating morphine antinociception tolerance.

Objective:To evaluate the relationship between milk fat globular epidermal growth factor Ⅷ (MFG-E8)-mediated efferocytosis and sepsis-associated encephalopathy (SAE) in mice.Methods:Forty clean-grade healthy male C57BL/6 mice, aged 2-3 months, weighing 18-22 g, were divided into 4 groups ( n=10 each) using a random number table method: sham operation group (group Sham), cecal ligation and perforation (CLP) group (group CLP), sham operation+ phosphate buffer solution (PBS) group (group Sham+ PBS) and CLP+ recombinant mouse MFG-E8 group (group CLP+ rmMFG-E8). SAE was induced by CLP in anesthetized mice.PBS 1 μl and rmMFG-E8 1 μg were injected into the lateral cerebral ventricle in Sham+ PBS and CLP+ rmMFG-E8 groups after operation for 5 consecutive days.Novel object recognition test was performed at 6 days after operation, and the contextual fear conditioning test was performed at 7 and 8 days after operation.The percentage of time spent exploring a novel object, discrimination index and percentage of freezing time induced by condition were calculated.The animals were sacrificed after the end of behavioral tests, and the hippocampus was extracted for determination of the expression of MFG-E8 and GTP-Rac1 (by Western blot), the mRNA expression levels of interleukin (IL)-6, tumor necrosis factor (TNF)-α and IL-1β (using real-time reverse transcription-polymerase chain reaction) and the apoptosis rate in hippocampus (by TUNEL). Results:Compared with group Sham, the percentage of time spent exploring a novel object, discrimination index and percentage of freezing time were significantly decreased, hippocamcal MFG-E8 expression was down-regulated, GTP-Rac1 expression was up-regulated, mRNA expression of IL-6, TNF-α and IL-1β was up-regulated, and apoptosis rate was increased in group CLP ( P<0.05). Compared with group CLP, the percentage of time spent exploring a novel object and discrimination index were significantly increased, freezing time was prolonged, hippocamcal MFG-E8 and GTP-Rac1 expression was up-regulated, mRNA expression of IL-6, TNF-α and IL-1β was down-regulated, and apoptosis rate was decreased in group CLP+ rmMFG-E8 ( P<0.05). Conclusion:The reduction of hippocampal MFG-E8-mediated efferocytosis may be involved in the pathophysiological mechanism of SAE in mice.