Somatosensory and Brainstem Auditory Evoked Potentials in the Gunn Rat Model of Acute Bilirubin Neurotoxicity

Abstract

Brainstem auditory evoked potentials (BAEPs) are a sensitive indicator of bilirubin neurotoxicity. Somatosensory evoked potentials (SEPs) have been proposed as another measure of toxicity, though the lemniscal pathways that generate the SEP are not involved in kernicterus. In 16 to 17-d-old jaundiced (jj) Gunn rats, serial BAEPs and SEPs were obtained up to 8 h after acute bilirubin toxicity. jjs were injected with 150 mg/kg sulfadimethoxine to displace bilirubin into brain tissue (n = 8); littermate controls were jjs given saline (n = 4) and nonjaundiced given sulfadimethoxine or saline (n = 7). After anesthesia, BAEP and SEP recordings were obtained at baseline and serially after injection. SEPs to median nerve stimulation were recorded from surface electrodes over the brachial plexus (Erb's) and contralateral parietal cortex, and subtracted to obtain central conduction time (CCT). There were no statistically significant different baseline values between groups. Baseline BAEP I, I-II, and I-III were 1.22 ± 0.13, 1.11 ± 0.12, and 2.10 ± 0.15 ms, and SEP Erb's and CCT were 1.48 ± 0.20 and 5.59 ± 0.50 ms, respectively (n = 19). At 6.8 ± 1.5 h after injection BAEP I, I-II, and I-III increased 0.10 ± 0.08, 0.18 ± 0.17, and 0.56 ± 0.33 ms over baseline, respectively (p = 0.005, 0.01, and 0.001, respectively, paired, 1-tailed t-tests), in experimental but not control groups. SEP Erb's decreased slightly, −0.06 ± 0.04 ms in experimental and −0.08 ± 0.08 ms in control groups, while CCT did not change significantly. BAEPs were completely abolished in two jjs with no SEP changes. When injection of sulfonamide induced significant peripheral and central BAEP abnormalities in jaundiced rats, no SEP abnormalities occurred. SEPs assess proprioception but not other somatosensory function or sensory integration. The results demonstrate the selectivity of acute bilirubin toxicity for the auditory nervous system.