Postnatal development of the brainstem auditory evoked potential and far-field cochlear microphonic in non-sedated rat pups.

Normal postnatal development of the scalp-recorded cochlear microphonic (CM) response and brainstem auditory evoked potential (BAEP) were studied in rat pups. BAEP latencies decreased and amplitudes increased as a function of maturation. These changes occurred rapidly between 14 and 23 days of age with gradual change occurring thereafter. The observed latency changes indicated that the auditory pathway matures in a sequential manner from the most peripheral to the most rostral structures. For example, CM latency stabilized (matured) by day 17 while BAEP wave I and II latencies stabilized by days 23 and 35, respectively. BAEP waves III and IV still showed significant latency decreases between days 42 and 70. The between-litter variability for CM and BAEP wave latencies also decreased with age. In contrast to peak latency measures, CM and BAEP amplitudes followed an independent time course of postnatal development. CM amplitude did not increase significantly after day 14. Amplitudes of all 4 BAEP components increased steadily from day 14 to 29, then stabilized. Unlike latency variability, amplitude variability was independent of age. There were no significant gender-dependent differences in amplitudes or latencies between the ages of 14 and 70 days.