Objective    To investigate the effects of extracellular signal-regulated protein kinase (ERK) 1/2 on the expression of bilirubin-induced nuclear transcription factor-κB (NF-κB) in rat’s hippocampal neurons

and to discuss the possible mechanism of ERK 1/2 signal pathway on preventing bilirubin neurotoxity in hippocampal neurons.     Methods    Hippocampal neurons cultured in vitro were randomly divided into a control group

a bilirubin group

a PD98059 (MEK/ERK inhibitor) + bilirubin group and an erucin (ERN

ERK activator) + bilirubin group. Modified MTT assay and Annexin V-FITC/PI dual fluorescent staining were employed to detect the relative survival rate and apoptosis rate of hippocampal neurons. Immunocytochemistry was employed to detect the expression of NF-κB p65 protein.     Results    There were statistical differences among the above four groups in terms of the relative survival rate of hippocampal neurons [100%

(67.546±3.241)%

(50.591±3.981)% and (80.020±8.552)%

P0.01]. There were statistical differences among the above four groups in terms of the apoptosis rate of hippocampal neurons[(6.859±1.559)%

(20.729±1.368)%

(28.474±1.710)%

and (13.741±5.150)%

P0.05]. At the same time point

there were statistical differences among the above four groups in terms of the mean optical density (MOD) of NF-κB (P0.01)

with the control group having the lowest value. In the bilirubin group

the MOD of NF-κB reached the highest value (0.266±0.033) at 3 h

decreased over time

and reached the lowest value (0.183±0.021) at 24 h (P0.01). The PD98059+bilirubin group had a similar trend

yet with a significantly decreased MOD (P0.05). In the ERN+bilirubin group

on the contrary

the MOD of NF-κB reached the lowest value (0.128±0.028) at 3 h

increased over time

and reached the highest value (0.305±0.043) at 24 h (P0.01).     Conclusion    In hippocampal neurons

bilirubin-induced NF-κB expression is in a time-dependent manner. ERK1/2 signal pathway protects hippocampal neurons from bilirubin-induced injury

and the protection mechanism may be related to the down-regulation of NF-κB early expression (3~6 h) and the up-regulation of NF-κB late expression (24 h).