Noise induced hearing loss and vestibular dysfunction in the guinea pig

Abstract This study analysed the acoustic and vestibular functional and morphological modifications in guinea pigs after acoustic trauma. Animals were exposed to noise (6 kHz, at 120 dB SPL for 60 minutes) and then auditory brainstem responses (ABR) and vestibuloocular reflex (VOR) were measured at 6 hours, 1 day, 3, 7, and 21 days after noise. Western blotting and immunostaining for 4-hydroxy-2-noneal (4-HNE) and vascular endothelial growth factor (VEGF) were performed in the cochlear and vestibular regions at 1 and 7 days after noise exposure. A significant decrease of VOR gain was observed on day 1 and the recovery was completed at day 21. ABR threshold values reached a level of 80 dB at day 1 after trauma reaching a value of about 50 dB SPL on day 21. 4-HNE expression, a marker of lipid peroxidation was strongly increased in the cochlea. In the vestibule, 4-HNE immunoreactivity was faint. However, VEGF was up-regulated both in the cochlea and vestibule. In conclusion, the expression of VEGF in both cochlear and vestibular structures suggests a reparative role with potentially therapeutic implications. Sumario Este estudio analiza las modificaciones vestibulares funcionales y morfológicas en los cobayos después de un trauma acústico. Los animales fueron expuestos a ruido (6kHz, a 120dB SPL durante 60 minutos) y se midieron las respuestas auditivas de tallo cerebral (ABR) y el reflejo vestíbulo-ocular (VOR); a las 6 horas, al siguiente día y los días 3, 7 y 21 después del ruido. Se realizaron pruebas de Western Blot e inmuno-reacciones para 4-hydroxi-2-noneal (4-HNE) y para factor de crecimiento vascular endotelial (VEGF) en las regiones coclear y vestibu-lar en los días 1 y 7 después de la exposición a ruido. Los resultados mostraron un descenso significativo de la ganancia del VOR en el día 1 y la recuperación fue completa en el día 21. Los umbrales de ABR llegaron a un nivel de 80dB en el día 1 después del trauma, alcanzando un valor de 50dB SPL en el día 21. El marcador 4-HNE, indicativo de peroxidación de los lípidos, estaba bastante aumentado en la cóclea. En la región vestibular, la reacción 4-HNE fue débil. Sin embargo, el VEGF se reguló por incremento tanto en la cóclea como en el vestíbulo. En conclusión, la expresión del VEGF en las estructuras tanto cocleares como vestibulares sugiere un papel reparador con potenciales implicaciones terapéuticas.

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