title: Tonotopic reorganization and spontaneous firing in inferior colliculus during both short and long recovery periods after noise overexposure.
abstract: BACKGROUND
  Noise induced injury of the cochlea causes shifts in activation thresholds and changes of frequency response in the inferior colliculus (IC). Noise overexposure also induces pathological changes in the cochlea, and is highly correlated to hearing loss. However, the underlying mechanism has not been fully elucidated. In this study, we hypothesized that overexposure to noise induces substantial electrophysiological changes in the IC of guinea pigs.
  
  
  RESULTS
  During the noise exposure experiment, the animals were undergoing a bilateral exposure to noise. Additionally, various techniques were employed including confocal microscopy for the detection of cochlea hair cells and single neuron recording for spontaneous firing activity measurement. There were alterations among three types of frequency response area (FRA) from sound pressure levels, including V-, M-, and N-types. Our results indicate that overexposure to noise generates different patterns in the FRAs. Following a short recovery (one day after the noise treatment), the percentage of V-type FRAs considerably decreased, whereas the percentage of M-types increased. This was often caused by a notch in the frequency response that occurred at 4 kHz (noise frequency). Following a long recovery from noise exposure (11-21 days), the percentage of V-types resumed to a normal level, but the portion of M-types remained high. Interestingly, the spontaneous firing in the IC was enhanced in both short and long recovery groups.
  
  
  CONCLUSIONS
  Our data suggest that noise overexposure changes the pattern of the FRAs and stimulates spontaneous firing in the IC in a unique way, which may likely relate to the mechanism of tinnitus.
authors: Feng
authors: F
authors: Wang
authors: Li
authors: L
authors: Zuo
authors: Bo
authors: B
authors: Hong
authors: Dongyi
authors: D
authors: Han
authors: Ethan M
authors: EM
authors: Range
authors: Lingyun
authors: L
authors: Zhao
authors: Yanan
authors: Y
authors: Sui
authors: Weiwei
authors: W
authors: Guo
authors: Department of Otolaryngology-Head and Neck Surgery, Chinese PLA General Hospital, Beijing 100853, China. labrat304@gmail.com.
authors: Liangfa
authors: L
authors: Liu
mesh_terms: D000200:Action Potentials; D000818:Animals; D003051:Cochlea / Q000293:injuries*; D005260:Female; D006168:Guinea Pigs; D006317:Hearing Loss, Noise-Induced / Q000209:etiology / Q000503:physiopathology*; D007245:Inferior Colliculi / Q000503:physiopathology*; D008297:Male; D009474:Neurons / Q000502:physiology*; D009622:Noise / Q000009:adverse effects; D013997:Time Factors; D014012:Tinnitus / Q000209:etiology / Q000503:physiopathology*