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Updated: Aug 4, 2026
In Ovo Electroporation in the Chicken Auditory Brainstem
Published on: June 9, 2017
Morphometric changes in the chick nucleus magnocellularis following acoustic overstimulation
J C Saunders1, H J Adler, Y E Cohen
1Department of Otorhinolaryngology: Head and Neck Surgery, University of Pennsylvania, Philadelphia 19104, USA. saunderj@mail.med.upenn.edu
Insights
Intense sound exposure shrinks nucleus magnocellularis (NM) cells in chicks, but cell size recovers within 43 days. NM structure and cell density remained unaffected by noise exposure.
Area of Science:
- Neuroscience
- Auditory Neuroscience
- Cell Biology
Background:
- Intense sound exposure can cause cochlear damage.
- The nucleus magnocellularis (NM) is a key auditory processing center in birds.
- Understanding the effects of acoustic trauma on neural structures is crucial for auditory research.
Purpose of the Study:
- To investigate the impact of intense sound-induced cochlear damage on the nucleus magnocellularis (NM) in neonatal chicks.
- To assess the structural recovery of NM cells following acoustic trauma.
- To correlate structural changes with functional recovery timelines.
Main Methods:
- Neonatal chicks were exposed to intense sound and allowed recovery periods of 0, 15, 27, and 43 days.
- Brainstems were processed, sectioned, and NM cells were measured for cross-sectional area.
- NM cell density was calculated at specific percentile positions.
- Age-matched control groups were used for comparison.
Main Results:
- Immediately after sound exposure, NM cell cross-sectional area was significantly reduced.
- NM cell size largely recovered to near-normal levels by 43 days post-exposure.
- The overall coronal area of the NM and NM cell density were not affected by sound exposure at any recovery interval.
Conclusions:
- NM cell size reduction following acoustic injury is reversible.
- Structural recovery of NM cells occurs despite prior functional restoration.
- Shrinkage may result from reduced cochlear nerve activity due to acoustic trauma.
Abstract:
The present investigation considered the effects of cochlear damage caused by exposure to intense sound on the nucleus magnocellularis of the chick. Neonatal chicks exposed to intense sound were separated into four groups with post-exposure recovery durations of 0, 15, 27, and 43 days. Four age-matched, non-exposed control groups were also formed. At each recovery interval, the control and exposed birds were sacrificed and their brains prepared for paraffin embedding. The brain stem region containing the nucleus magnocellularis (NM) was serially sectioned in the coronal plane. All sections containing NM cells were identified and then coded in terms of their percentile distance from the most caudolateral section. Sections along the nucleus at the 15th, 30th, 50th, 65th, 80th, and 95th percentile positions were selected for evaluation, and the cross-sectional areas of individual NM cells in these sections were then measured. Cell areas were corrected for the bias introduced by eccentricity of the nucleus. The number of NM cells per 1,000 microm2 was also calculated at the 50th and 65th percentile positions. These procedures were repeated for the age-matched, non-exposed control animals. The cross-sectional cell area in exposed animals, immediately after the exposure, was reduced significantly at all positions, but returned to near normal by 43 days of recovery. However, the coronal area of NM in the sections at the 50th and 65th percentile position, as well as NM cell density, were unaffected by the exposure at all recovery intervals. The observation of structural recovery in NM cells at 43 days post-exposure was remarkable because it occurred at least 4 weeks after complete functional restoration of single-cell activity in the NM. The shrinkage in NM cell size throughout the nucleus may be due to a general reduction in spontaneous activity in the cochlear nerve fibers caused by the acoustic injury to the chick basilar papilla.
