Pain Mechanisms and Sensory NeuroscienceResearch PaperRelationship between noise-induced hearing-loss, persistent tinnitus and growth-associated protein-43 expression in the rat cochlear nucleus: does synaptic plasticity in ventral cochlear nucleus suppress tinnitus?
Highlights
▶Adult rats were unilaterally exposed to narrow-band noise centered at 12 kHz at 126 dB for 2 h. ▶Noise exposure causes hair cell loss, auditory nerve degeneration, and synaptic growth in the VCN. ▶Noise causes tinnitus in some but not all rats despite same pattern of hair cell loss. ▶No-Tinnitus rats show more GAP-43 expression in VCN than Tinnitus rats 10 weeks after noise. ▶Long-term synaptic plasticity in ventral cochlear nucleus may suppress noise-induced tinnitus.
Section snippets
Animals
Twelve adult male Sprague–Dawley rats (Sasco, Charles River Laboratories International, Inc., Wilmington, MA, USA) were used for this study. Nine experimental rats were unilaterally exposed to high-intensity noise in order to induce tinnitus-like behavior in some rats. Rats were screened for tinnitus before and after the noise exposure using gap prepulse inhibition of acoustic startle (GPIAS) as described below and subsequently separated into two following groups: “Noise-No-Tinnitus” and
Tinnitus screening
All experimental rats and age-matched controls were screened for tinnitus-like behavior with the GPIAS paradigm before noise exposure (“Baseline”), days 1–10 after exposure (“Short-term”), and weeks 8–10 after exposure (“Long term;” Fig. 3). Startle amplitudes at the “no-gap” condition were present in all rats at baseline as well as after noise exposure showing that all rats were capable of a significant startle response. At baseline, all rats showed significant inhibition of startle amplitude
Discussion
Unilateral exposure to narrow-band noise centered at 12 kHz and presented at 126 dB SPL for two h caused nearly complete loss of IHC and OHC in the exposed ear except in the extreme apex. In contrast, little or no hair cell loss was observed in the opposite plugged ear. Ten weeks after exposure, eight rats showed strong expression of GAP-43 in the auditory nerve and medial VCN on the noise-exposed side but not in lateral VCN or in DCN. Up-regulation of GAP-43 in medial VCN was significantly
Acknowledgments
We thank Dr. Paul Allen at the University at Rochester for generously sharing the custom software for startle reflex testing. This project was supported by grant from NIH (R.S., R01 DC009091 and R01DC009219).
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