The effects of chronic tinnitus caused by acoustic trauma on social behaviour and anxiety in rats

Tinnitus is associated with significant increases in anxiety disorders in humans, which is thought to affect social interaction; however, there has been only one previous study of the effects of tinnitus on social interaction in animals treated with salicylate and no previous study of the effects of tinnitus on anxiety in animals. In the present study, we used acoustic trauma to induce tinnitus in rats and investigated its effects on social interaction and anxiety in animals confirmed to have tinnitus. When social behaviours were grouped, we found that animals with tinnitus engaged in significantly more aggressive behaviours toward both tinnitus and sham control animals (P=0.03). When individual social behaviours were analysed without considering whether a tinnitus or sham animal was interacting with a member of its own treatment group, tinnitus animals were found to engage in significantly more anogenital investigation (P=0.01) and significantly less social grooming (P=0.003). When the data were analysed according to whether an animal was interacting with a member of its own group, tinnitus animals were found to bite sham animals significantly more than other tinnitus animals (P=0.005). Sham animals also bit tinnitus animals significantly more than other sham animals (P=0.02), as well as climbing away from them more (P=0.04), kicking (P=0.003), nudging them more (P=0.04), and sleeping with them more (P=0.02). By contrast, sham animals sniffed tinnitus animals significantly less than sham animals (P=0.05). There were no significant differences between the sham and tinnitus animals in performance in the elevated plus and elevated T maze tests of anxiety. However, tinnitus animals displayed a slight but significant increase in locomotor activity in the open field (P=0.04). These data suggest that tinnitus results in complex changes in social interaction in rats, which are not due simply to increases in anxiety.