Succinate dehydrogenase (SDH) activity in hair cells: a correlate for permanent threshold elevations

Area of Science:

• Auditory Neuroscience
• Ototoxicity Research
• Cellular Biology

Background:

• Hair cell loss is a common indicator of hearing loss, but histological and physiological data often lack strong correlation.
• The precise histological basis for potentiation of noise-induced auditory threshold elevation by carbon monoxide (CO) remains unclear.

Purpose of the Study:

• To investigate succinate dehydrogenase (SDH) activity in hair cells as a marker for cellular dysfunction and auditory sensitivity loss.
• To explore the histological basis of carbon monoxide's potentiation of noise-induced hearing loss.

Main Methods:

• Rats were exposed to octave-band noise (100 dB, 13.6 kHz, 2 h) or noise combined with carbon monoxide (1200 ppm).
• Compound action potential (CAP) threshold elevations and cochlear histological changes were assessed 4 weeks post-exposure.
• Succinate dehydrogenase (SDH) activity in hair cells was measured as an indicator of cellular function.

Main Results:

• Noise exposure alone caused elevated CAP thresholds with minimal hair cell loss but reduced SDH activity, particularly in inner hair cells, correlating with auditory sensitivity loss.
• Combined noise and CO exposure resulted in more severe CAP threshold elevation and SDH reduction, along with significant outer hair cell loss.
• Neither hair cell loss nor SDH reduction alone strongly correlated with auditory sensitivity reduction across all frequencies.

Conclusions:

• SDH activity reduction in inner hair cells is a sensitive indicator of auditory sensitivity loss, especially at low frequencies where hair cell loss is absent.
• Outer hair cell loss is associated with high-frequency hearing sensitivity reduction.
• The combined effects of noise and CO on auditory sensitivity involve complex interactions between hair cell integrity and metabolic activity.