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Development of the middle ear in neonatal chinchillas. I. Birth to 14 days
G S Hsu1, R H Margolis, P A Schachern
1Otitis Media Clinical Research Center and Department of Otolaryngology, UniversitY of Minnesota School of Medicine, Minneapolis, USA.
Insights
Middle ear function in young chinchillas shows immature acoustic admittance, but hearing sensitivity is mature at birth. Structural analysis revealed no fetal tissue, suggesting other factors influence middle ear development.
Area of Science:
- Otolaryngology
- Developmental Biology
- Auditory Neuroscience
Background:
- Human middle ear function varies significantly with age, contrasting with mature hearing sensitivity at birth.
- Hypotheses for developmental changes include immature ear canal walls and persistent fetal tissue.
- Understanding these changes is crucial for diagnosing auditory development issues.
Purpose of the Study:
- To investigate the relationship between middle ear function, hearing sensitivity, and middle ear structure in neonatal chinchillas.
- To assess developmental changes in middle ear acoustics and anatomy from birth up to 14 days.
- To evaluate the presence of fetal tissue in the developing chinchilla ear.
Main Methods:
- Multifrequency tympanometry (226–2,000 Hz) assessed middle ear function.
- Auditory brainstem response measured hearing sensitivity (clicks, 1–8 kHz tone bursts).
- Histologic analysis of temporal bones examined structural characteristics.
Main Results:
- Neonatal chinchillas exhibited low acoustic admittance and complex tympanometry, unlike adults.
- Acoustic admittance remained constant from 1 to 14 days, suggesting later developmental changes.
- Hearing sensitivity was mature at birth; no significant age-related structural changes or fetal tissue were found.
Conclusions:
- Chinchilla hearing is mature at birth, but middle ear function is not.
- Developmental changes in chinchilla middle ear function occur over a longer period than studied.
- The absence of fetal tissue suggests other factors contribute to middle ear development differences.
Abstract:
Measures of middle-ear function in humans show large differences among neonates, infants, and adults. In contrast, hearing sensitivity is essentially mature at birth. Hypotheses that have been proposed to explain the developmental changes in middle-ear function include: (i) contaminating effects of the immature neonatal ear-canal wall and (ii) persistent fetal tissue in the ear canal, tympanic membrane (TM), and middle-ear space. To better understand the relationships between middle-ear function, hearing sensitivity and the structure of the middle ear, 30 chinchillas, aged 1-14 days, were studied. Middle-ear function was assessed by multifrequency tympanometry with probe tones ranging from 226 to 2,000 Hz. Hearing sensitivity was measured by auditory brainstem response using clicks and 1, 2, 4, and 8 kHz tone bursts. Structural characteristics were analyzed from temporal bone histologic preparations. At all frequencies, the acoustic admittance of the neonatal car is very low and tympanometric patterns are complex and irregular, compared to adult animals. The admittance is essentially constant from 1 to 14 days, indicating that developmental changes occur over a much wider age span than that investigated here. Hearing sensitivity of the chinchilla appears to be mature at birth. Histologic analysis indicated that there were no age-related changes in TM thickness, TM diameter, distance from TM to promontory, and stapes footplate diameter. There were small increases in bone thickness, middle-ear area, mastoid bulla area, and in the perimeters of the middle ear and mastoid bulla. There were no significant amounts of loose mesenchyme or other fetal tissue in the middle-ear space.
