Dual Isoflurane-induced Preconditioning Improves Neuroprotection in Rat Brain In Vitro and the Role of Extracellular Signal-regulated Protein Kinase

Abstract

To test the ability of isoflurane-induced preconditioning against oxygen and glucose deprivation (OGD) injury in vitro. Rat hippocampal slices were exposed to 1 volume percentage (vol%), 2vol% or 3vol% isoflurane respectively for 20 minutes under normoxic conditions (95% O₂/5% CO₂) once or twice (12 slices in each group) before OGD, with 15-minute washout after each exposure. During OGD experiments, hippocampus slices were bathed with artificial cerebrospinal fluid (ACSF) lacking glucose and perfused with 95% N₂ and 5% CO₂ for 14 minutes, followed by a 30-minute reperfusion in normal ACSF. The CA1 population spike (PS) was measured and used to quantify the degree of neuronal function recovery after OGD. To assess the role of mitogen-activated protein kinases (MAPKs) in isoflurane preconditioning, U0126, an inhibitor of extracellular signal-regulated protein kinase (ERK1/2), and SB203580, an inhibitor of p38 MAPK, were used before two periods of 3vol% isoflurane exposure. The degree of neuronal function recovery of hippocampal slices exposed to 1vol%, 2vol%, or 3vol% isoflurane once was 41.88%±9.23%, 55.05% ± 11.02%, or 63.18% ± 10.82% respectively. Moreover, neuronal function recovery of hippocampal slices exposed to 1vol%, 2vol%, or 3vol% isoflurane twice was 53.75% ± 12.04%, 63.50% ± 11.06%, or 76.25% ± 12.25%, respectively. Isoflurane preconditioning increased the neuronal function recovery in a dose-dependent manner. U0126 blocked the preconditioning induced by dual exposure to 3vol% isoflurane (6.13% ± 1.56%, P < 0.01) and ERK1/2 activities. Isoflurane is capable of inducing preconditioning in hippocampal slices in vitro in a dose-dependent manner, and dual exposure to isoflurane with a lower concentration is more effective in triggering preconditioning than a single exposure. Isoflurane-induced neuroprotection might be involved with ERK1/2 activities.