| Tinnitus and hearing loss are the frequent auditory-related co-morbidities of blast trauma. The etiology of blast-induced tinnitus is also muddled by brain mechanisms associated with emotional and cognitive problems such as anxiety, memory loss, and depression. We set out to develop a realistic and ecologically valid model to address changes of cognitive status and psychological state that are associated with blast- induced tinnitus. In this study, 19 adult rats were randomly divided into the sham group (n=6) and the blast group (n=13). Blast exposure (14 psi) was conducted via a shock wave tube to expose the left ears of the rats in the blast group, and a sham exposure was conducted to the rats in the sham group. Blast-induced tinnitus was evaluated with gap detection and pre-pulse inhibition (PPI) acoustic startle reflex paradigms; the changes of thresholds of the hearing was evaluated with auditory brainstem response (ABRs), the change in the level of anxiety was evaluated with elevated plus maze; and the change in the status of memory was evaluated with one-day Morris water maze. To investigate blast-induced neuronal changes in the limbic structures, we utilized MEMRI technique. Obtained with MRIcro, MR intensity signal-to-noise ratios (SNRs) of 83 selected limbic structures were measured to represent the level of synaptic activity. Of the 13 rats that were exposed to blast shock wave, 8 rats developed chronic tinnitus on post-exposure day 35 (PED35) and 5 rats did not. Our results showed that compared to rats in the sham group (n=6), (1) rats in the blast group with or without tinnitus demonstrated higher level of anxiety (p<0.05); (2) rats in the blast group that exhibited behavioral evidences of tinnitus (n=8) demonstrated neuronal hyperactivity in bilateral amygdaloidal complex, specifically bilateral basolateral groups and the left cortical-like group of the amygdala (p<0.05); and (3) rats in the blast group demonstrated neuronal hyperactivity in bilateral nucleus accumbens core (p<0.05). In conclusion, the elevated level of synaptic activity in the bilateral amygdala and nucleus accumbens core indicates central plasticity associated with blast-induced tinnitus. |
