| Background:Postoperative cognitive dysfunction (POCD) is a serious complication after surgery. Advanced age and severe surgical trauma are two main risk factors for POCD. Though the pathogenesis of POCD remains unclear, trauma induced neuroinflammation plays a key role in the disease process. Blood-brain barrier (BBB) is a dynamic interference that regulates the nutrition and toxic substance in and out of the central nervous system (CNS), and plays a crucial role in maintaining a stable circumstance of the CNS. Based on recent findings, it has been suggested that surgery adversely affects the BBB permeability and function. Mast cells are distributed in a variety of anatomical sites, including the CNS, where they are located perivascularly, capture and respond to immune signals from the blood at the first time. There is substantial evidence suggests that mast cells can promote the BBB breakdown. Therefore, we hypothesized that the activation of mast cells may drive BBB breakdown and thereby impact cognitive dysfunction secondary to peripheral surgery. Object:To investigate the effect of mast cells on BBB and their relationship with POCD.Methods:A total of 128 adult male Sprague-Dawley ratswere randomly allocated to four groups:(i) i.c.v. injection of normal saline (Ctrl group); (ii) i.c.v. injection of cromolyn (Cro group); (iii) tibial fracture surgery following i.c.v. injection of normal saline (Op group); (iv) tibial fracture surgery following i.c.v. injection of cromolyn (Cro+op group). Rats in the Cro group and Cro+op group received 200 μg/2μl cromolyn i.c.v. 30 min before surgery, while the others received an equivalent volume of normal saline.Every group was divided into 1 day group and 3 day group. Hippocampal sections were stained in 0.05% toluidine blue or tryptase for mast cell staining. Contextual fear conditioning and Y maze are used to assess learning and memory. The mRNA level of TNF-α and IL-1β in hippocampus was determined by Real-time PCR. BBB permeability of the rat brain was determined by Evans blue extravasation. The expression of occludin and claudin-5 was assessed by western blot analysis. The expression of MMP-2 and MMP-9 was determined by western blot analysis and immunochemistry.Results:As compared to controls,the mast cell number increased in hippocampal area CA1 of adult rats that underwent tibial fracture surgery at day 1 (P<0.01) and day 3 (P<0.01), which was inhibited by i.c.v. injection of cromolyn (day1:P<0.01, day 3:P<0.05 or P<0.01). Compared to controls, the rats exposed to surgery exhibited a significant reduction in cognitive function at day 1 (P<0.01) and day 3 (P<0.01). Treatment with cromolyn significantly improved freezing behavior and the number of learning trials on dayl (P<0.01) and day 3 (P<0.05 or P<0.01), respectively. One day following surgery, mRNA levels of TNF-α and IL-1βin the hippocampus significantly increased (P<0.01). Pre-treatment with cromolyn partially abolished the increase in surgery-induced TNF-α and IL-1β production (P<0.01). At day 3, mRNA expression of IL-1β of Op group remained high (P<0.01) and the effect of cromolyn on IL-1β mRNA expression still existed (P<0.05). At day 1,EB content of the hippocampus was significantly increased in the Op group (P<0.01) as compared with Ctrl group. Prophylactic cromolyn significantly decreased the EB quantification (P<0.01). At day 3, there was no difference between four groups. One day following surgery, occludin and claudin-5 levels of the hippocampus significantly decreased in the Op groupas compared with Ctrl group (P<0.01).Pre-treatment with cromolyn partially reserved this effect (P<0.05). At day 3, there was no difference between the four groups. At day 1,MMP-2 and MMP-9 expression of surgery-exposed rats was significantly higher than the expression in control rats (P<0.01),which was reversed by cromolyn (P<0.01),a result confirmed by immunohistochemical staining (P< 0.05 or P< 0.01).At day 3,both expression of MMP-2 and MMP-9 returned to baseline level.Conclusion:The present study identifies that the mast cell number increased in hippocampal area CA1 of adult rats that underwent tibial fracture surgery at day 1 and day 3, which was related to BBB disruption, CNS inflammation and cognitive dysfunction. |
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