Objective     To determine the effects of

prematurity

hypoxia and hyperoxia preconditioning on bilirubin neurotoxicity.     Methods     Seventy-two 7-day-old rats in full-term group and premature group (36 in each group)

were randomly divided into 6 subgroups

control group

bilirubin group

hypoxia group

hyperoxia group

hypoxia+bilirubin group

and hyperoxia+bilirubin group (n=6). After the rats were kept in a chamber of 95%O

2

(for hyperoxia groups) or 8% O

2

(for hypoxia groups) for 3 h

0.02 ml normal saline or 10 mg/ml bilirubin at 20 μg/g body weight was injected into the cerebellomedullary cistern in control group and bilirubin groups. After behavior evaluation at 24 h after injection

the rats were sacrificed

and their brain tissues were collected. The apoptosis and necrosis of neurocytes

the expressions of iNOS and TNF-α in the hippocampus were detected by HE staining

TUNEL and immunohistochemical staining

respectively.     Results     The rats in the bilirubin groups appeared to have different degrees of abnormal behaviors

such as proneness

tumble

limbs twitched

rolled and less activity. These behaviors were more obvious in the premature rats. HE staining showed that the apoptosis and necrosis of neurocytes in hypoxia+bilirubin group were more significant than in the other groups. TUNEL showed that compared with the bilirubin group in full-term mice (23.33±4.89)

the apoptotic rate in the hippocampus of bilirubin group in premature mice (30.17±3.76) was significantly increased (P0.05); Compared with the bilirubin groups of full-term and premature mice (23.33±4.89 and 30.17±3.76)

the apoptosis rates of the corresponding hypoxia+bilirubin groups (27.67±3.01 and 34.33±3.01) were increased dramatically (P0.05); whereas those of hyperoxia+bilirubin groups didn’t not show obviously increase (P0.05). Immunohistochemistry showed

compared with the rats in full-term bilirubin group

TNF-α in the hippocampus of bilirubin premature mice (0.425±0.014) was increased significantly (P0.05)

while the expression of iNOS (0.253

±0.009) was not significantly increased

and the expression of iNOS (0.437±0.024) and TNF-α (0.440±0.001) in hypoxia+bilirubin group was increased remarkably (P0.05). In contrast

in hyperoxia+bilirubin group

the expression of iNOS (0.254±0.010) was not obviously increased (P0.05)

whereas the release of TNF-α (0.416±0.011) was not significantly increase (P0.05).     Conclusion     Bilirubin aggravates the damage of hippocampus neurocytes by inducing cell apoptosis and releasing TNF-α. Hypoxia and prematurity improve the expression and releases of inflammatory factors and deteriorate bilirubin neurotoxicity. To control perinatal asphyxia and prematurity and  inhibit bilirubin-induced inflammation play vital role in prophylaxis of bilirubin encephalopathy.