Relationship between anxiety and tinnitus development in a rat model

Tinnitus, the auditory perception of sound without an external environmental stimulus, affects 15 % of the human population and is associated with hearing loss. Interestingly, anxiety may be a significant risk factor in tinnitus pathophysiology potentially due to underlying common neural circuits of the auditory and limbic systems. The current study aimed to investigate the effects of stress-induced anxiety on tinnitus development in a rat model. Neonatal dexamethasone (DEX) exposure was used to mimic early life stress with the aim of inducing an anxiety-like phenotype in adulthood. These animals were then exposed to an acoustic trauma (AT) to investigate proportion and time to tinnitus development. DEX exposure (n = 18) induced changes in anxiety-like behaviour, compared to vehicle control animals (n = 15), with increased anxiety-like behaviour in acoustic startle response tests but not in the Elevated Plus Maze. There was no difference in the proportion of animals that developed behavioural signs of tinnitus between DEX and control groups, however, animals that developed behavioural signs of tinnitus had higher levels of anxiety prior to AT. Furthermore, neuronal recordings in the medial geniculate nucleus, a region crucial in the gating of non-salient auditory information, indicated that rats with behavioural signs of tinnitus had elevated spontaneous and burst firing rates compared to rats without behavioural signs of tinnitus. Overall, these findings further illuminate our understanding of the relationship between anxiety and susceptibility to tinnitus development, and are consistent with the body of clinical literature highlighting the correlation between anxiety and tinnitus percept.