A behavioral paradigm to judge acute sodium salicylate-induced sound experience in rats: a new approach for an animal model on tinnitus.

Behavioral conditioning studies on rats have been proven to be a valid animal model for the evaluation of acute and chronic phantom auditory experience (tinnitus). We developed an animal model for short-term, acute induced phantom auditory sensations in rats. Rats were trained in a conditioning chamber to actively access a liquid feeder whenever a constant white noise sound was present. During silence, no reward was given. Fulfilling the demands of animal protection laws for maximal avoidance of pain and fear, punitive paradigms were maximally reduced. After 15-17 learning sessions, all animals performed more accesses to the reward feeder during periods of sound than during periods of silence. Tinnitus was induced by the administration of sodium salicylate (350 mg/kg body weight) given 3 h before testing. The feeder access activity of a rat treated with salicylate was significantly increased during periods of silence, indicating a phantom auditory experience. The presumptive auditory experience was estimated to be comparable to a white noise sound of about 30 dB SPL rms. The activity increase was less pronounced for lower doses of sodium salicylate (150 mg/kg body weight) and was not found in animals trained on a dark-light paradigm, as expected. As the learning sessions of the operant conditioning were performed without pharmacological treatment, unintentional drug effects, for example, on learning and motivation of a rat were minimized in this behavioral paradigm. Furthermore, the behavioral changes reported here were shown to be a specific drug effect evoking a phantom auditory experience of a rat and cannot be explained by unspecific drug effects on motor activity, motivation, learning or hearing loss. The conditional paradigm is discussed in the context of its potential as a model for testing drugs that may have a therapeutic value in tinnitus research.