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Prolonged sound exposure has different effects on increasing neuronal size in the auditory cortex and brainstem
1Department of Physiology, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan; Tzu Hui Institute of Technology, Nanzhou Township, Pingtung, Taiwan.
Hearing Research
|June 10, 2014
Summary
Sound exposure after the critical period can enlarge neurons in the auditory cortex and brainstem of young rats. This delayed plasticity occurs in both regions, with greater changes observed in the midbrain.
Area of Science:
- Neuroscience
- Auditory System Plasticity
- Developmental Neurobiology
Background:
- The auditory cortex can exhibit neuronal plasticity even after the critical period.
- It is unclear if this delayed plasticity is confined to the cortex or involves subcortical structures like the brainstem.
Purpose of the Study:
- To compare the effects of sound exposure on neuronal size in the auditory cortex and midbrain of young rats.
- To investigate the timing and extent of delayed auditory plasticity.
Main Methods:
- Young rats (postnatal day 22) were exposed to a 4 kHz tone (65 dB SPL) for 3 or 7 days.
- Neuronal size was analyzed morphometrically in the auditory cortex and midbrain.
- Histological sections (7 μm) were examined.
Main Results:
- Sound exposure significantly increased neuronal size in the auditory cortex (32%) and midbrain (67%).
- Midbrain neuronal enlargement occurred in both low and high-frequency regions, while cortical changes were mainly in high-frequency areas.
- Cortical changes were evident by day 29, with slight enlargement by day 22, suggesting synchronized or slightly preceded subcortical changes.
- No neuronal size changes were observed in the cochlear nucleus or visual midbrain.
Conclusions:
- Delayed auditory plasticity extends beyond the auditory cortex to subcortical structures like the midbrain.
- The observed differential effects suggest complex mechanisms beyond simple activity-driven changes, potentially involving the descending auditory system.
