Salicylate induces anxiety-like behaviour and slow theta oscillation and abolishes the relationship between running speed and fast theta oscillation frequency

Salicylate intoxication is a cause of tinnitus in humans and it is often used to produce tinnitus‐like perception in animal models. Here we assess whether salicylate induces anxiety‐like electrophysiological and behavioural signs. Using microwire electrode arrays, we recorded local field potential in the ventral and, in some experiments dorsal hippocampus, in an open field arena 1 hour after salicylate (300mg/kg) injection. We found that animals treated with salicylate moved dramatically less than saline treated animals. Salicylate‐treated animals showed a strong 4‐6Hz (type 2) oscillation in the ventral hippocampus (with smaller peaks in dorsal hippocampus electrodes). Coherence in the 4‐6Hz‐theta band was low in the ventral and dorsal hippocampus when compared to movement‐related theta coherence (7‐10Hz). Moreover, movement related theta oscillation frequency decreased and its dependency on running speed was abolished. Our results suggest that salicylate‐induced theta is mostly restricted to the ventral hippocampus. Slow theta has been classically associated to anxiety‐like behaviours. Here we show that salicylate application can consistently generate low frequency theta in the ventral hippocampus. Tinnitus and anxiety show strong comorbidity and the increase in ventral hippocampus low frequency theta could be part of this association.