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Previous studies have shown that intermittent hypobaric hypoxia (IH) preconditioning protected neurons survival from brain ischemia. However, the mechanism remains to be elucidated. The present study explored the role of nitric oxide (NO) in the process by measuring the expression of NO synthase (NOS) and NO levels. Male Wistar rats (100) were randomly assigned into four groups: sham group, IH + sham group, ischemia group and IH + ischemia group. Rats for IH preconditioning were exposed to hypobaric hypoxia mimicking 5000 m high-altitude (PB = 404 mmHg, PO2 = 84 mmHg) 6 h/day, once daily for 28 days. Global brain ischemia was established by four-vessel occlusion that has been created by Pulsinelli. Rats were sacrificed at 7th day after the ischemia for neuropathological evaluation by thionin stain. In addition, the expression of neuronal NOS (nNOS), inducible NOS (iNOS), and NO content in the hippocampal CA1 subfield were measured at 2nd day and 7th day after the ischemia. Results revealed that global brain ischemia engendered delayed neuronal death (DND), both nNOS and iNOS expression up-regulated, and NO content increased in the hippocampal CA1 subfield. IH preconditioning reduced neuronal injury induced by the ischemia, and prevented the up-regulation of NOS expression and NO production. In addition, L-NAME + ischemia group was designed to detect whether depressing NO production could alleviate the DND. Pre-administration of L-NAME alleviated DND induced by the ischemia. These results suggest that IH preconditioning plays a protective role by inhibiting the over expression of NOS and NO content after brain ischemia. [ABSTRACT FROM AUTHOR]

Highlights • Global brain ischemia caused delayed neuronal death(DND) in CA1 hippocampus in rats. • The ischemia led to GLT-1 down-regulation and p-p38 MAPK up-regulation in rats. • Lethal OGD decreased GLT-1 and increased p-p38 MAPK expression in astrocytes. • SB203580 or p38 MAPK siRNA reduced neuronal death and GLT-1 decreasing after OGD. • SB203580 alleviated the DND and GLT-1 down-regulation after brain ischemia in rats. Abstract The previous studies have shown that glial glutamate transporter-1 (GLT-1) participates in cerebral ischemic injury in rats. However, the mechanism involved remains to be elucidated. This study was undertaken to investigate whether p38 MAPK was involved in regulating GLT-1 in the process. At first, it was observed that global brain ischemia for 8 min led to obvious delayed neuronal death, GLT-1 down-regulation and p-p38 MAPK up-regulation in CA1 hippocampus in rats. Then, whether p-p38 MAPK was involved in regulating GLT-1 during cerebral ischemic injury was studied in vitro. Astrocyte-neuron co-cultures exposed to oxygen and glucose deprivation (OGD) were used to mimic brain ischemia. It was observed that lethal OGD (4-h OGD) decreased GLT-1 expression and increased p-p38 MAPK expression in astrocytes. The p-p38 MAPK protein rised from 0 min to 48 h that is the end time of the observation, and the peak value was at 12 h, which was 12.45 times of the control group. Moreover, pre-administration of p38 MAPK inhibitor SB203580 or its siRNA dose-dependently increased GLT-1 expression, and meanwhile alleviated the neuronal death induced by lethal OGD. The above results indicated that p38 MAPK signaling pathway participated in regulating GLT-1 during OGD injury in vitro. Finally, back to in vivo experiment, it was found that pre-administration of SB203580 by intracerebroventricular injection dose-dependently reversed the down-regulation of GLT-1 expression and attenuated the delayed neuronal death normally induced by global brain ischemia in CA1 hippocampus in rats. Taken together, it can be concluded that the mechanism of GLT-1 mediating cerebral ischemic injury depends on the activation of p38 MAPK. [ABSTRACT FROM AUTHOR]