Abstract
To compare the development of the auditory system in hearing and completely acoustically deprived animals, naive congenitally deaf white cats (CDCs) and hearing controls (HCs) were investigated at different developmental stages from birth till adulthood. The CDCs had no hearing experience before the acute experiment. In both groups of animals, responses to cochlear implant stimulation were acutely assessed. Electrically evoked auditory brainstem responses (E-ABRs) were recorded with monopolar stimulation at different current levels. CDCs demonstrated extensive development of E-ABRs, from first signs of responses at postnatal (p.n.) day 3 through appearance of all waves of brainstem response at day 8 p.n. to mature responses around day 90 p.n.. Wave I of E-ABRs could not be distinguished from the artifact in majority of CDCs, whereas in HCs, it was clearly separated from the stimulus artifact. Waves II, III, and IV demonstrated higher thresholds in CDCs, whereas this difference was not found for wave V. Amplitudes of wave III were significantly higher in HCs, whereas wave V amplitudes were significantly higher in CDCs. No differences in latencies were observed between the animal groups. These data demonstrate significant postnatal subcortical development in absence of hearing, and also divergent effects of deafness on early waves II–IV and wave V of the E-ABR.
Highlights
The auditory system demonstrates extensive developmental changes during postnatal life, both in humans as well as in altricial animals
Wave I of evoked auditory brainstem responses (E-auditory brainstem responses (ABRs)) could not be distinguished from the artifact in majority of congenitally deaf white cats (CDCs), whereas in hearing controls (HCs), it was clearly separated from the stimulus artifact
Electrical stimulation of the auditory nerve may yield a different extent of activation in the central auditory system in deafened animals
Summary
The auditory system demonstrates extensive developmental changes during postnatal life, both in humans as well as in altricial animals (review in [1]). Extensive changes in the auditory cortex have been demonstrated in adult CDCs [7] as well as in neonatallydeafened cats [8] Many of these changes are the consequence of an altered postnatal developmental sequence [9]. Electrically-evoked auditory brainstem responses (E-ABRs) are used clinically in human cochlear implanted subjects to objectively assess the auditory function [18,19,20]. The present data reveal that auditory deprivation does affect the brainstem and that these functional effects can be detected using E-ABRs. The data demonstrate that a significant portion of the developmental process is, preserved in complete deafness. The present data show that different portions of the afferent auditory pathway are differentially sensitive to deprivation
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