Changes in the brainstem auditory evoked response of the rabbit during the first postnatal month.

Brainstem auditory evoked responses (BAERs) were recorded in 73 albino rabbits during the first postnatal month. Responses could not be evoked before the ninth day post-term using free field click stimulation at 60 dBHL. The onset of BAERs to these stimuli on or after day 9 was coincident with the onset of behavioural responses to sounds and, in the majority of animals, with eye opening. The onset of BAERs was delayed in animals with low body weight. The intensity required to evoke detectable BAERs in normally grown animals decreased rapidly after day 9 post-term. The most significant changes in the form of the BAER in the first postnatal month were an increase in the amplitude of peak III and the separation of peaks IV and V. Peak I and the negative dip after peak V (Vn) were consistent features of the BAER during development. The latencies of these deflections and the interval between them decreased by approximately 1.5 and 4 ms respectively up to the end of the first month post-term. On days 9 and 10 post-term, stimulation at a higher rate (40 Hz) failed to evoke a BAER in some animals. In other animals the change in stimulation rate from 10 to 40 Hz produced a large increase in the latency of peak V. The unusually large changes in the latencies of peaks and the interpeak intervals during the development of the rabbit indicate that this animal may be particularly suitable for studies of perinatal complications on development of the brainstem when the BAER is to be used as non-invasive measure of neural function.