| Thirty-two tammar wallabies, aged between postnatal days (PND) 96 and 293, were used to study the auditory development. The auditory brainstem responses (ABR) were obtained from anaesthetized animal before craniotomy, which exposed the right side of the brain.; The wallaby's auditory system generates auditory evoked potentials from PND 90 and undergoes an important development between PND 90 and 140, during which the number of the ABR components increases from only one positive peak to 5 positive components.; The functional development of the wallaby auditory brainstem takes an ascending sequence. The earliest age, at which the focal response is recorded, is PND 101 for the auditory nerve root (ANR), PND 110 for the cochlear nucleus (CN), PND 112 for the superior olive (SO) and PND 114 for the inferior colliculus (IC).; At PND 101, the auditory nerve is the only functional auditory station after the cochlea, and the ABR is a single positive deflection, corresponding in time to the ANR response.; At PND 110, when the CN response is first recorded, the ABR is a positive-negative deflection. Meanwhile, responses of the ANR and CN occur in the time span of the positive peak of the ABR, with the main component of the CN response corresponding to the second half of the ABR P wave.; Between PND 112 and 140, the threshold and latency of the SO response decrease and the amplitude increases. Auditory adaptation in the SO response, defined as a reduction in amplitude of the evoked potential and an increase in its latency during repetitive stimulation, is more pronounced with increased stimulus intensity and presentation rate, but becomes less pronounced with age from PND 112 until 160 PND, longer than the developmental period of response threshold, latency and amplitude.; At PND 114, auditory response is first detected from the rostral pole of the IC. With development, more caudal parts of the IC show auditory responses until all parts of the IC are responsive to sound at around PND 125. The threshold and latency of the IC response decrease and its amplitude increases until adult-like values are reached at about PND 160. The main component of the IC response is a negative wave. (Abstract shortened by UMI.)... |
