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Updated: Aug 30, 2026
Auditory Brainstem Response and Outer Hair Cell Whole-cell Patch Clamp Recording in Postnatal Rats
Published on: May 24, 2018
Mild carbon monoxide exposure diminishes selectively the integrity of the cochlea of the developing rat
Ivan Lopez1, Dora Acuna, Douglas S Webber
1Surgery Department, Division of Head and Neck, David Geffen School of Medicine, Los Angeles, California 90095, USA. ivan@hnsurg.medsch.ucla.edu
Insights
Chronic carbon monoxide (CO) exposure in developing rats affects the auditory system. Mild CO exposure caused nerve swelling and reduced key enzymes in the cochlea and spiral ganglion.
Area of Science:
- Neuroscience
- Auditory System Research
- Toxicology
Background:
- The peripheral auditory system's development is sensitive to environmental factors.
- Chronic exposure to low levels of carbon monoxide (CO) may impact neurodevelopment.
- Understanding CO's effects on the auditory system is crucial for public health.
Purpose of the Study:
- To investigate the effects of chronic, low-level carbon monoxide (CO) exposure on the developing peripheral auditory system in rat pups.
- To analyze morphological and biochemical changes in the organ of Corti and spiral ganglion.
Main Methods:
- Rat pups were exposed to 12 or 25 ppm CO from postnatal day 8 to 22.
- Morphological analysis using immunochemical and histological techniques.
- Assessment of key enzymes and protein markers (e.g., Cytochrome oxidase, Synaptophysin).
Main Results:
- No significant changes in inner and outer hair cells at 12 or 25 ppm CO.
- Swollen nerve terminals innervating inner hair cells observed at 25 ppm CO.
- Reduced levels of Cytochrome oxidase, NADH-TR, and calcium ATPase at 25 ppm CO.
- Decreased immunostaining for neurofilament and myelin basic proteins.
Conclusions:
- Mild chronic CO exposure during development selectively impacts cochlear components.
- Auditory system development is vulnerable to low-level CO toxicity.
- Specific enzymes and proteins in the cochlea and spiral ganglion are affected by CO exposure.
Abstract:
Rat pups were chronically exposed to carbon monoxide (CO) concentrations (12 or 25 ppm) in air starting at day 8, through 22 days of age, to examine the changes in the peripheral auditory system. Gastrostomy-reared rat pups, with or without CO exposure, were used and compared with mother-reared pups. The organ of Corti and the neurons of the spiral ganglion were analyzed for their morphology by using immunochemical and histological techniques. The inner and outer hair cells in the organ of Corti of animals exposed to 12 and 25 ppm CO were not different from the controls. However, at 25 ppm CO exposure, the nerve terminals innervating the inner hair cells were swollen. The somata of neurons in the spiral ganglion showed mild changes in the cytoplasm, and signs of mild vacuolization were observed in myelin covering their central processes. Synaptophysin, a marker for synaptic vesicles, and choline acetyltransferase, a marker for cholinergic terminals, showed no difference in immunoreactivity in CO exposed animals at 12 and at 25 ppm when compared with their age-matched controls. Also, Na(+)K(+) ATPase immunoreactivity patterns were normal compared with controls. Three enzymes were significantly reduced at the 25 ppm CO exposure: Cytochrome oxidase, NADH-TR, and calcium ATPase were decreased in both the organ of Corti and the neurons of the spiral ganglion, and decreased immunostaining for the neurofilament and myelin basic proteins was found. We conclude that components of the cochlea are selectively affected by mild chronic CO exposure during development.
