Both JNK and P38 MAPK pathways participate in the protection by dexmedetomidine against isoflurane-induced neuroapoptosis in the hippocampus of neonatal rats

Dexmedetomidine, a highly selective α2-adrenergic agonist, has been reported to attenuate isoflurane-induced cognitive impairment and neuroapoptosis. However, the underlying molecular mechanisms remain poorly understood. The aim of this study was to investigate whether mitogen-activated protein kinase (MAPK) pathway was involved in dexmedetomidine-induced neuroprotection against isoflurane effects. Seven-day-old (P7) neonatal Sprague-Dawley rats were pretreated with various concentrations of dexmedetomidine, and then exposed to 0.75% isoflurane or air for 6h. Terminal deoxyribonucleotide transferase-mediated dUTP nick end labeling (TUNEL) was used to detect neuronal apoptosis in their hippocampus. Activated caspase-3, extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH2-terminal kinases (JNK), p38, phospho-ERK1/2, phospho-JNK and phospho-p38 proteins were detected by Western blotting in the hippocampus at the end of exposure. Also, P7 rats were pretreated with 75 μg/kg dexmedetomidine alone, or given the ERK inhibitor U0126 before dexmedetomidine pretreatment, or pretreated with the p38 MAPK inhibitor SB203580 or JNK inhibitor SP600125 alone, and then exposed to 0.75% isoflurane for 6h. Isoflurane induced significant neuroapoptosis, increased the protein expression of phospho-JNK, phospho-c-Jun, phospho-p38 and phospho-nuclear factor-κB (NF-κB), decreased the level of phospho-ERK1/2 protein and reduced the ratio of Bcl-2/Bax in the hippocampus. Dexmedetomidine pretreatment inhibited isoflurane-induced neuroapoptosis and restored proteins expression of MAPK pathways and the Bcl-2/Bax ratio after isoflurane exposure. Moreover, SB203580 and SP600125 also partly attenuated the isoflurane-induced protein changes. However, U0126 did not reverse dexmedetomidine-induced neuroprotection. Our results indicate that the JNK and p38 pathways, not the ERK pathway are involved in dexmedetomidine-induced neuroprotection against isoflurane effects.