Study Of Dexmedetomidine Alleviates Cerebral Ischemia/Reperfusion Injury And Neuron Apoptosis Through P38 MAPK Signaling Pathway In Rat

Background The brain is very sensitive to ischemia and hypoxia, which can cause irreversible neurological damage. If ischemia exceeds a certain period of time, recovery of blood flow often cause further damage to the brain tissue. It called ischemia/ reperfusion injury(I/RI). During the perioperative period, especially in the perioperative period with high risk, which is simultaneous with cerebrovascular accident. The direction of clinicians is prevention of cerebrovascular adverse events.Mitogen-activated protein kinase(MAPK) family is a set of intracellular serine/threonine protein kinases. Some studies have reported that the p38 MAPK signaling pathway in the MAPK family is activated in the brain tissue after I/R,participates in cell apoptosis.Dexmedetomidine(Dex) is a highly selective alpha 2 adrenoceptor agonist. A great deal of studies has confirmed the cerebral protective effects ofdexmedetomidine, and its protective mechanism has also been revealed, but research about the molecular signal transduction pathway is still in the initial stage. It is not confirmed whether the protective effects of dexmedetomidine on cerebral I/R through inhibition of p38 MAPK signaling pathway.In this study, we established local cerebral I/R injury model using the method of middle cerebral artery occlusion to observe the neuroprotective effects of dexmedetomidine on local cerebral I/RI. Through the observations of p38 MAPK signal transduction pathway after dexmedetomidine treatment and inhibiting the activation of alpha 2 receptors and p38 MAPK signaling pathway, we discuss the mechanism of p38 MAPK signaling pathway about how it works in neuroprotective effects of dexmedetomidine on cerebral I/RI.Objectives To establish the rat cerebral artery I/R model and treat the rat model with dexmedetomidine, yohimbine, SB203580, and to observe the symptoms of neurological damage, brain edema, cerebral infarction, brain cortical neuron apoptosis and p-p38 expression in rats. To verify the the neuroprotective effects of dexmedetomidine against local cerebral I/RI and to study the mechanism of p38 MAPK pathway in this process.Methods1 Experimental grouping: the rats were randomly divided into for groups of 8with 18 rats in each group: sham control group: Sham+Dex group, Sham+SB group,Sham+Yoh+Dex group, I/R group, I/R+Dex group, I/R+SB group, I/R+Yoh+Dex group.2 Establishment of cerebral I/R model: Thread the suture into the middle cerebral artery from the left external carotid artery of rats, and pull out the suture 90 min later to achieve reperfusion. The suture are not thread into the middle cerebral artery in Sham operation.3 The NDS score: 0 for no obvious symptoms of neurological damage; 1 for left anterior limb flexion, failure to fully extended when the tail is raised. 2 for circleing to the left side when moving but maintaining balance at rest. 3 for dumping to left side when moving and standing instability; 4 for failure to walk, consciousness disappear.4 Evaluation of animal model: excluding the following rat: suture insertion depth less than 17 mm, excessie intraoperative blood loss, the formation of thrombus in basilar artery, SAH, no symptoms of nerve injury, consciousness loss or failure to survive at the observe time.5 Administration: dexmedetomidine 3 ?g/kg within 5 min when ischemia begining, then 6 ?g/kg/h for 2 h, i.v. The control group was administrated with the same amount of NS. SB203580 0.1 nmol/L, 30 min before ischemia, i.c.v. Yohimbine0.5 mg/kg, 30 min before ischemia, i.p.6 Measure of cerebral edema and infarct volume: the percentage of ischemic side increased volume and the percentage of infarct volume was calculated after TTC staining.7 The expression of cleaved caspase-3 and p-p38 in ischemic brain tissue is detected by immunofluorescence stain, and the coexpression of p-p38/Neu N, GFAP and Ox-42 observed by immunefluorescent double labeled staining.8 The expression of p-p38 and p38 was detected by Western blotting analysis and immunostaining.Results1 Evaluation of I/R model: the success rate of MCAO model was about 66.1%.2 The NDS score, cerebral edema, infarct volume,brain ischemic area of Cleaved-Caspase-3 expression: Sham control group, Sham+Dex group, Sham+SB group and Sham+Yoh+Dex group has no difference. I/R group was higher than Sham group. I/R+Dex group was significantly lower than I/R group. I/R+SB group was lower than I/R group, but higher than I/R+Dex group. I/R+Yoh+Dex group was lower than I/R group, but higher than I/R+Dex group.(P < 0.05)3 The number of p-p38 positive cells and the ratio of p-p38/p38 in ischemic brain tissue: Sham control group, Sham+Dex group, Sham+SB group and Sham+Yoh+Dex group was not different. I/R group was higher than Sham group.I/R+Dex group was lower than I/R group. I/R+SB group was lower than I/R group,but higher than I/R+Dex group. I/R+Yoh+Dex group was lower than I/R group, but higher than I/R+Dex group.(P < 0.05)4 p-p38/Neu N and p-p38/GFAP double immunohistochemical detection has few consistent distribution area; p-p38/OX-42 has more uniformly distributed areaConclusion1 Dexmedetomidine has neuroprotective effects to alleviate the local cerebral I/RI and inhibit neuron apoptosis.2 p38 MAPK pathway is involved in the neuroprotective effects of dexmedetomidine on cerebral I/RI.3 In rats with focal cerebral I/R model, effects of dexmedetomidine on p38 MAPK pathway incompletely depend on alpha 2 adrenergic receptor.