Brainstem auditory evoked potentials correlate with morphological changes in Gunn rat pups

Abstract

The relationship of brainstem structure and function in bilirubin encephalopathy is incompletely understood. The present experiments compare quantitative measures of brainstem structures with brainstem auditory evoked potentials (BAEPs) in infant jaundiced (jj) and nonjaundiced (Nj) Gunn rats. Ten jj's from 4 litters were injected with sulfadimethoxine at 11–12 days of age to raise their brain bilirubin concentration. Littermate controls were jj's given saline, and Nj's given sulfadimethoxine or saline. At 15–17 days of age BAEPs were recorded, and rats were prepared for histological examination, as was reported in the previous paper (Conlee and Shapiro. 1991). Significant differences between groups were seen for BAEP wave I latency ( P = 0.002), I–II interwave interval ( P = 0.001), and amplitudes of waves I, II, III, and IV (each P <0.0005) due to increased latencies and decreased amplitudes in the jj-sulfa group. Animals with the most severe BAEP abnormalities had the most severe histological abnormalities. Cochlear nucleus volume had a positive linear correlation with the amplitude of BAEP waves I. II, and IV, and an inverse correlation with wave I latency and I–II interwave interval ( P ≦ 0.001). The highest correlations were BAEP I–II interwave interval and amplitude of waves I and II with cochlear nucleus volume ( r = −0.78, 0.71 and 0.70, respectively, P < 0.0005). In the cochlear nucleus, spherical cell area correlated with wave I latency and amplitude, and wave III amplitude ( P < 0.001), the I–II interwave interval, and the amplitudes of waves II and IV ( P < 0.01). In contrast, globular cells, which were not affected anatomically, did not correlate significantly with later BAEP waves. Cell area in the nucleus of the trapezoid body correlated with amplitude of I and II ( P < 0.01). There were no significant correlations of cell area in the superior olive with any of the BAEP values. These results show that BAEPs are sensitive indicators of morphometric abnormalities in the brainstem of jaundiced Gunn rats, and help to establish the predictive validity of BAEPs in determining the specific sites of bilirubin-induced brain damage.