Differential impact of temporary and permanent noise-induced hearing loss on neuronal cell density in the mouse central auditory pathway.
Although acoustic overstimulation has a major pathophysiological influence on the inner ear, central components of the auditory pathway can also be affected by noise-induced hearing loss (NIHL). The present study investigates the influence of a noise-induced temporary threshold shift (TTS) and/or permanent threshold shift (PTS) on neuronal cell densities in key structures of the central auditory pathway. Mice were noise-exposed (3 h, 5-20 kHz) at 115 dB sound pressure level (SPL) under anesthesia, and were investigated immediately (TTS group, n = 5) after the exposure, or 1 week later (PTS group, n = 6). Unexposed animals were used as controls (n = 7). Frequency-specific auditory brainstem responses (ABR) were recorded to examine auditory thresholds. Cell density was determined within the dorsal (DCN) and ventral (VCN) cochlear nucleus; the central nucleus of the inferior colliculus (ICC); the dorsal, ventral, and medial subdivisions of the medial geniculate body (MGBd, MGBv, and MGBm); and layer I to VI of the primary auditory cortex (AI I-VI). ABR thresholds were significantly elevated in the TTS group (52-69 dB SPL) and in the PTS group (33-42 dB SPL) compared to controls. There was a significant decrease in cell density only in the VCN of the TTS group (-10%), most likely induced by the acute overstimulation of neurons. Cell density was significantly reduced in all investigated auditory structures at 1 week post-exposure (PTS group), except in layer II of the AI (VCN: -30% and DCN: -30% (high-frequency); -39% (low-frequency); ICC: -31%; MGBd: -31%; MGBm: -28%; MGBv: -31%; AI: -10 to 14%). Thus there were dramatic changes within the neuronal cytoarchitecture of the central auditory pathway following a single noise exposure. The present findings should help clinicians to better understand the complex psychoacoustic phenomena of NIHL.
Gröschel
Moritz
M
Department of Otolaryngology at ukb, Charité Medical School, Berlin, Germany.
Götze
Romy
R
Ernst
Arne
A
Basta
Dietmar
D
D000818:Animals; D001303:Auditory Cortex / Q000473:pathology; D001306:Auditory Pathways / Q000473:pathology*; D001309:Auditory Threshold / Q000502:physiology; D002452:Cell Count; D017626:Cochlear Nucleus / Q000473:pathology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005260:Female; D005829:Geniculate Bodies / Q000473:pathology; D006317:Hearing Loss, Noise-Induced / Q000473:pathology*; D007245:Inferior Colliculi / Q000473:pathology; D008297:Male; D051379:Mice; D009474:Neurons / Q000473:pathology*; D016707:Tissue Fixation