OBJECTIVETo probe the changes of fast component of brainstem auditory evoked potentials (FC-BAEP), slow component of brainstem auditory evoked potentials (SC-BAEP) and the mitochondrial ultrastructures of the neurons in the brainstem in the rat pups with hyperbilirubinemia.

METHODS7 days old SD rat pups were randomly divided into control group (C, 17 rat pups) and two test groups (T1, 17 rat pups and T2, 17 rat pups). Bilirubin solutions (2 g/L) were injected into the abdominal cavity of the rat pups in the group T1 and T2 at the postnatal day 7 and 10. Six hours after the second injection, seven rat pups of each group were randomly selected to test serum bilirubin concentration via a micro-gauge. FC-BAEP and SC-BAEP were examined with an evoked potential recorder in the rest rat pups of each group at postnatal day 17 and 20. At the postnatal day 20, the endocardial perfusion was performed in these rat pups for the fixation of the brain, and then the brains were taken out. The cochlear nuclei were used for observation via electron microscope.

RESULTSSix hours after the injection of bilirubin solution at the postnatal day 10, the serum bilirubin concentrations of the rat pups in group T1 and T2 were increased significantly. Except for II-IV inter-peak latency(IPL), all the peak latency(PL) and IPL of FC-BAEP evoked via three sound stimulating rates (10/s, 40/s,80/s) at the postnatal day 17 prolonged significantly in the rat pups of group T1 and T2, and the PL in group T2 were much longer than that in group T1. Except for II-IV IPL of FC-BAEP evoked via sound stimulating rates of 10/s and 40/s, all the PL and IPL at the postnatal day 20 prolonged significantly in the rat pups of group T1 and T2. The PL of SC-BAEP evoked via sound stimulating rate of 10/s at the postnatal day 17 and 20 in the rat pups of group T1 and T2 prolonged significantly, and the PL at the postnatal day 17 in group T2 were much longer than that of group T1. The changes of mitochondria of the neurons in the cochlear nuclei at the postnatal day 20 in the rat pups of group T1 and T2 were characterized by swell, the slurred membranes, the broken crista and so on.

CONCLUSIONThere were the abnormal changes of FC-BAEP, SC-BAEP and the mitochondrial ultrastructures of the neurons in the brainstem in the rat pups with hyperbilirubinemia. The PL and IPL of FC-BAEP and SC-BAEP could be taken as the objective and sensitive indexes for early monitoring the bilirubin-induced hearing loss and brain injury.