Recovery of hair cells was studied at various times after acoustic trauma in adult quail. An initial loss of hair cells recovered to within 5 percent of the original number of cells. Tritium-labeled thymidine was injected after this acoustic trauma to determine if mitosis played a role in recovery of hair cells. Within 10 days of acoustic trauma, incorporation of [3H]thymidine was seen over the nuclei of hair cells and supporting cells in the region of initial hair cell loss. Thus, hair cell regeneration can occur after embryonic terminal mitosis.

Williams syndrome (WS) is a genetic neurodevelopmental disorder, most often accompanied by mild-to-moderate mental retardation. Individuals with WS show unique communication strengths and impairments that are challenging to treat in community, educational, and vocational settings. Many issues regarding characteristics of auditory sensitivity in WS remain to be resolved. Our purpose was to obtain behavioral (screening and pure-tone audiometry) and objective (distortion product otoacoustic emission-DPOAE) measures of auditory system function from a group of 27 individuals with WS, 6-48 years of age. These measures were gathered both at an international professional conference (n = 19) and in a clinic setting (n = 8). In the behavioral screening conditions, 16/19 (84%) of the individuals failed the hearing screening; and in the behavioral diagnostic hearing condition, 6/8 (75%) demonstrated sensorineural hearing loss (SNHL) and 1/8 demonstrated a hearing loss of undetermined type. In the objective DPOAE testing, 19/25 (76%) had DPOAE absolute amplitudes below the 5th percentile for ears with normal hearing [Gorga et al. (1997); Ear Hear 18(6):440-455]. We report SNHL in 14/18 (78%) of school-age children with WS. Post hoc analyses revealed a significant effect for age, suggesting a pattern of progressive hearing loss. An effect size analysis indicated a clinically meaningful difference in the hearing sensitivity between school-aged children and adults in the high frequencies (4,000 and 8,000 Hz). Similar hearing loss phenotype was observed in patients with familial nonsyndromic supravalvular aortic stenosis (SVAS), suggesting that molecular defects in the elastin gene in the pathogenesis of SNHL in WS. This study highlights the importance of early and regular hearing testing for WS patients and suggests that elastin may have a previously unappreciated function in maintaining hearing sensitivity.

Developmental changes in the site of receptor damage following pure-tone acoustic overstimulation were examined in the basilar papillae of embryonic and hatchling chickens. During development, a systematic shift in the position of damage toward the apex of the cochlea was produced by each of three frequencies, suggesting that the transduction properties of the sensory epithelium systematically shift with age. These results imply that neurons in the central nervous system may be maximally stimulated by different sounds during development.

No abstract

Postmitotic hair-cell regeneration in the inner ear of birds provides an opportunity to study the effect of renewed auditory input on auditory perception, vocal production, and vocal learning in a vertebrate. We used behavioral conditioning to test both perception and vocal production in a small Australian parrot, the budgerigar. Results show that both auditory perception and vocal production are disrupted when hair cells are damaged or lost but that these behaviors return to near normal over time. Precision in vocal production completely recovers well before recovery of full auditory function. These results may have particular relevance for understanding the relation between hearing loss and human speech production especially where there is consideration of an auditory prosthetic device. The present results show, at least for a bird, that even limited recovery of auditory input soon after deafening can support full recovery of vocal precision.The avian inner ear provides a useful model for the study of hair-cell regeneration and recovery in the vertebrate ear, but the ultimate value of this regenerative capacity depends on whether it results in functional recovery of auditory and vocal behavior (1-3). In response to either acoustic trauma or insult from ototoxic drugs, both young and adult birds show a temporary period of hair-cell loss and regeneration, usually culminating in considerable anatomical, physiological, and behavioral recovery within several weeks (4-12). Behavioral recovery, as typically defined, refers only to a return of absolute auditory sensitivity to near pretrauma levels (13-16). Much less is known about the recovery of more complex auditory behavior, and nothing is known about the effect of hearing loss and recovery on the production or recognition of learned vocalizations. Though evolutionarily distant from humans, birds provide the only animal model for studying hearing restoration by renewed sensory-cell input and for examining the effect of such recovery on learned vocalizations. The question is whether a ''new'' auditory periphery results in sufficient functional recovery that a bird can again perceive, learn, and produce complex acoustic communication signals. The nature of this recovery bears on fundamental issues in auditory plasticity and sensorimotor interfaces. Moreover, the ability to track the time course of such recovery in a vertebrate auditory system may have particular significance for the effective use of auditory prosthetic devices, such as cochlear implants, for the severely hearing impaired (17).Budgerigars (domesticated parakeets), learn new vocalizations throughout life, especially in response to changes in their social milieu (18)(19)(20). Further, our work, as well as the work of others, has shown that these birds experience hair-cell loss and threshold shift after administration of the ototoxic drug kanamycin followed, within several days or weeks, by hair-cell regeneration and a gradual recovery to within 20 dB of normal auditory sensitivity (21,22). In th...