gms | German Medical Science

Introduction: Recently, we reported on stress-induced hypersensitivity, which persisted until 24 h following the rats’ exposure. Simultaneously, the concentrations of corticosterone and TNFa increased in serum. The expression of genes associated with the HPA axis like GR and Hif1a increased in the inferior colliculus (IC), and in the spiral ganglion (SG) to a lesser extent. In the organ of Corti, the mRNA expression of prestin was up-regulated. Here, we analyzed the gene expression of further hypoxia- and stress-related genes in the IC and SG.

Methods: Adult Wistar rats had been exposed to a rodent repellent in their cages for 24 h (61–65 dB SPL, 300 Hz, 1/s, 15-s interval). Immediately, 3, 6 and 24 h as well as 7 days after the exposure, we analyzed the gene expression in the SG and CI (real-time RT-PCR, 2-ΔΔct, reference gene: ribosomal subunit 16). Non-exposed animals served as controls.

Results: In the SG, the mRNA expressions of iNos and Hsf1 transcripts significantly increased 24 h post-stress. In the IC, these genes were already up-regulated immediately and after 3 h. Simultaneously, the Tnfa and Tnfar were up-regulated. We also found up-regulations of the Sp, Ngfb and Sod2 immediately and of Cox2 3 h post-stress. After 24 h, the expression of Hsp70 was up-regulated. All gene expressions were on the basal level after 7 days.

Conclusion: The 24-h exposure to stress induced temporary up-regulations of hypoxia-related and regeneration genes in the auditory system of the rat. In the IC, these changes were found to be earlier and more pronounced than in the SG indicating that tissue of the central auditory system reacts more sensitively to activation of the HPA axis than tissue of the peripheral auditory system in our model.