The Effects of Baclofen on Chronic Tinnitus Induced By Acoustic Trauma

Abstract

Tinnitus is characterised by a phantom ringing in the ear. Approximately twelve million Americans experience tinnitus in a form severe enough to require medical attention. Despite this prevalence there is no effective treatment available due to the uncertain pathophysiology underlining tinnitus. Acoustic trauma is the most common cause of tinnitus and is often associated with neuronal hyperactivity in the central auditory system. Hence any drug that increases GABAergic neurotransmission within the central nervous system, such as baclofen, would decrease hyperactivity and thus alleviate tinnitus. To test this, sixteen Wistar rats were divided into sham (n = 8) and tinnitus (n = 8) groups. Tinnitus was induced by unilateral exposure to acoustic trauma and the presence of tinnitus was assessed by a frequency-specific shift in the discrimination function with a conditioned lick suppression paradigm. Hearing thresholds were also examined by acoustic brainstem-evoked responses (ABR). Once tinnitus was confirmed, the animals were injected with saline (vehicle) followed by baclofen at three different doses (1, 3 and 5 mg/kg) and reassessed for the presence or absence of tinnitus. Acoustic trauma significantly increased the ABR thresholds in the exposed ear and caused a significant downshift in the frequency-response curve in the noise exposed animals, which was indicative of tinnitus. Baclofen alleviated tinnitus like behaviour with the best results achieved at the 5mg/kg dose. However future research is required to determine optimal dose range and optimal treatment duration to ensure complete alleviation of tinnitus in both animals and human beings.