Blast-induced tinnitus and spontaneous activity changes in the rat inferior colliculus

• Blast exposure induces onset behavioral evidence of tinnitus in rats.
• Blast exposure induces onset hyperactivity in all frequency regions of the inferior colliculus.
• The induced hyperactivity becomes more robust toward a high frequency region over time.
• Blast also induces increased bursting activity in the inferior colliculus.

High-pressure blast shockwaves are known to cause tinnitus. Imaging studies have shown that blast-induced tinnitus may result from damage to the inner ear structures and/or direct brain impact that trigger a cascade of neuroplastic changes in both auditory and non-auditory centers. Nevertheless, information is still lacking on the neurophysiological mechanisms underlying blast-induced tinnitus. In this study, we used a rat model and investigated the effect of blast-induced tinnitus on spontaneous activity in the inferior colliculus (IC) at one day, one month, and three months following blast. Our results showed that rats with behavioral evidence of tinnitus exhibited hyperactivity in all frequency regions at one day post-blast. Although the induced hyperactivity persisted throughout a three-month recording period, it was more robust in middle frequency loci at one month after blast exposure and in middle-to-high-frequency loci at three months after blast. Our results also showed increased bursting rate in the low and middle frequency regions at one day after blast, in the middle frequency region at one month after blast, and in all frequency regions at three months after blast. The findings suggest that neuroplasticity as reflected by shifted tonotopic representations of hyperactivity and bursting activity subserves blast-induced tinnitus and hearing impairment.