Role of hippocampal ERK1/2 in exogenous carbon monoxide-induced improvement of cognitive function in a rat model of hemorrhage shock and resuscitation

Abstract

Objective To evaluate the role of hippocampal extracellular signal-regulated kinase 1/2 (ERK1/2) in exogenous carbon monoxide(CO)-induced improvement of cognitive function in a rat model of hemorrhage shock and resuscitation. Methods Ninety clean-grade healthy male Sprague-Dawley rats, aged 9-10 weeks, weighing 350-400 g, were divided into 5 groups (n=18 each) using a random number table method: sham operation group (S group), hemorrhage shock and resuscitation group (H group), CO group, PD98059-CO group (PCO group) and PD98059 group (P group). Hemorrhagic shock was induced by withdrawing blood from the femoral vein until mean arterial pressure was reduced to 25-35 mmHg which was maintained for 60 min and resuscitated by infusing the blood withdrawn over 15 min until the initial blood pressure was achieved, and normal saline was infused when needed.Rats were exposed to air mixture containing 1% CO for 3 h in a glass box after the end of resuscitation in group CO.ERK1/2 inhibitor PD98059 (30 μmol/L) 30 μl was injected into the cerebral ventricle at 30 min before hemorrhage in PCO and PC groups.Right femoral artery and vein were only cannulated, and normal saline was injected into the cerebral ventricle in group S. Rats were sacrificed at 3 h after the end of resuscitation, brains were removed and hippocampi were isolated for determination of CO content (by gas chromatograph assay). Cognitive function was assessed by Morris water maze test at 15 days after the end of resuscitation, rats were then sacrificed and hippocampi were isolated for determination of cell apoptosis in hippocampal CA1 region by TUNEL and cleaved caspase-3 immunofluorescence, and the apoptosis rate was calculated.Rats were sacrificed at 6 h after the end of resuscitation, and hippocampi were isolated to detect the expression of phosphorylated ERK1/2 (p-ERK1/2), Bcl-2 and Bax by Western blot. Results Compared with group S, the escape latency was significantly prolonged in H, PCO and P groups, and the hippocampal CO content and apoptosis rate were increased, the expression of cleaved caspase-3 and ERK1/2 was up-regulated, and the Bcl-2/Bax ratio was decreased in H, CO, PCO and P groups (P<0.05). Compared with group H, the escape latency was significantly shortened, the hippocampal CO content was increased, and the apoptosis rate was decreased, the cleaved caspase-3 expression was down-regulated, p-ERK1/2 expression was up-regulated, and Bcl-2/Bax ratio was increased in group CO, and the escape latency was significantly prolonged, the hippocampal CO content was decreased, the apoptosis rate was increased, the cleaved caspase-3 expression was up-regulated, p-ERK1/2 expression was down-regulated, and Bcl-2/Bax ratio was decreased in group P (P<0.05). Compared with group CO, the escape latency was significantly prolonged, the apoptosis rate was increased, the cleaved caspase-3 expression was up-regulated, p-ERK1/2 expression was down-regulated, and Bcl-2/Bax ratio was decreased in group PCO (P<0.05). Conclusion The mechanism by which exogenous CO improves cognitive function is related to raising the phosphorylation of ERK1/2 in hippocampal neurons and inhibiting neuronal apoptosis in a rat model of hemorrhage shock and resuscitation. Key words: Extracellular signal-regulated MAP kinases; Carbon monoxide; Reperfusion injury; Hippocampus; Apoptosis; Cognition disorders