Prenatal low dosage dioxin (TCDD) exposure impairs cochlear function resulting in auditory neuropathy

Area of Science:

• Environmental Toxicology
• Developmental Biology
• Auditory Neuroscience

Background:

• 2,3,7,8-tetrachorodibenzo-p-dioxin (TCDD) is a persistent environmental contaminant and potent teratogen.
• Aryl hydrocarbon receptor (AhR) mediates TCDD toxicity, but its normal function is unclear.
• Hair cell development is critical for cochlear function.

Purpose of the Study:

• To investigate if dioxin exposure during critical hair cell development disrupts cochlear function.
• To compare the effects of TCDD exposure across three mouse strains with different AhR-b alleles.

Main Methods:

• Pregnant mice (C57BL/6, BalbC, CBA) received TCDD or vehicle on embryonic day 12.
• Cochlear function was assessed at 1.5 months using auditory brainstem responses (ABRs) and distortion-product otoacoustic emissions (DPOAEs).
• ABRs measured hearing thresholds, while DPOAEs assessed outer hair cell function.

Main Results:

• TCDD exposure significantly elevated ABR thresholds in C57BL/6 mice (Ahb-1 allele), indicating hearing impairment.
• BalbC and CBA mice (Ahb-2 allele) showed no significant elevation in ABR thresholds.
• DPOAEs were unaffected in all strains, suggesting a mild auditory neuropathy in susceptible mice.

Conclusions:

• The Ahb-1 allele confers susceptibility to TCDD-induced hearing deficits.
• Auditory brainstem response testing may serve as a sensitive biomarker for TCDD toxicity.
• Developmental dioxin exposure could be a risk factor for auditory neuropathy.