The effects of JNK pathway on isoflurane induced neuronal apoptosis in the hippocampi of neonatal rats

Abstract

Objective To investigate the effects of the c-Jun N-terminal kinase (JNK)pathway on isoflurane induced neuronal apoptosis and the proteins expression of phospho-JNK, Bcl-2 and Bax in the hippocampi of neonatal rats. Methods Forty-eight neonatal rats at postnatal day 7 (P7) were randomly assigned into 4 groups: DMSO control group (group D), SP600125 control group (group SP30), isoflurane+ DMSO group (group Iso+ D), isoflurane+ SP600125 group (group Iso+ SP30). Rats were exposed to air (control group) or 1.1% isoflurane (isoflurane group) for 4 h. The JNK inhibitor SP600125 at 30 μg or 12% DMSO 5 μl was intraventricularly administered 20 min before the exposure. The brains of some rats in each group were perfused and embedded by paraffin 6 h after the exposure. Neuronal apoptosis in the hippocampi CA1 area was detected by TUNEL (n=6). The fresh hippocampi of other rats in each group were dissected 6 h after the exposure and the proteins expression of phospho-JNK, Bcl-2 and Bax were detected by Western blot (n=6). One way ANOVA were used for data analysis among groups. Results The number of TUNEL positive cells in the hippocampal CA1 regions in group Iso+ D (135.72±21.26 per mm2) increased by 5 folds compared with group D (24.07±1.35 per mm2) (P<0.01); while the number of apoptotic cells in group Iso+ SP30 (42.49±5.56 per mm2) decreased by 84%(P<0.05)compared with group Iso+ D. The expression of phospho-JNK p46 kd in group Iso+ D increased by 44.1%(P<0.01), while both phospho-JNK at p46kd and at p54kd in group Iso+ SP30 decreased significantly (P<0.05, P<0.01) compared with group Iso+ D. The protein expression of Bax increased 1.5 folds (P<0.05) and Bcl-2 decreased by 42.2% (P<0.05) in group Iso+ D compared to group D; while SP600125 significantly decreased expression of Bax (P<0.05) and increased expression of Bcl-2 (P<0.01). Conclusion JNK activation contributes to isoflurane-induced neuroapoptosis in the developing brain. Maintaining Bcl-2 expression and inhibiting Bax expression may be involved in the neuroprotective effects of SP600125. Key words: Apoptosis; Isoflurane; C-Jun N-terminal kinase; Hippocampus