Abstract
Tinnitus has been suggested to arise from neuronal hyperactivity in auditory areas of the brain, and anti-epileptic drugs are sometimes used to provide relief from tinnitus. Recently, the anti-epileptic properties of the cannabinoid drugs have gained increasing interest; however, the use of cannabinoids as a form of treatment for tinnitus is controversial. In this study, we tested whether a combination of delta-9-tetrahydrocannabinol (delta-9-THC) and cannabidiol (CBD), delivered in a 1:1 ratio, could affect tinnitus perception in a rat model of acoustic trauma-induced tinnitus. Following sham treatment or acoustic trauma, the animals were divided into the following groups: (1) sham (i.e., no acoustic trauma) with vehicle treatment; (2) sham with drug treatment (i.e., delta-9-THC + CBD); (3) acoustic trauma-exposed exhibiting tinnitus, with drug treatment; and (4) acoustic trauma-exposed exhibiting no tinnitus, with drug treatment. The animals received either the vehicle or the cannabinoid drugs every day, 30 min before the tinnitus behavioral testing. Acoustic trauma caused a significant increase in the auditory brainstem response (ABR) thresholds in the exposed animals, indicating hearing loss; however, there was a partial recovery over 6 months. Acoustic trauma did not always result in tinnitus; however, among those that did exhibit tinnitus, some of them had tinnitus at multiple frequencies while others had it only at a single frequency. The cannabinoids significantly increased the number of tinnitus animals in the exposed-tinnitus group, but not in the sham group. The results suggest that cannabinoids may promote the development of tinnitus, especially when there is pre-existing hearing damage.
Highlights
Tinnitus is the perception and conscious awareness of sound that is not physically present
In general, acoustic trauma resulted in a frequency-dependent increase in the auditory brainstem response (ABR) thresholds in the ipsilateral ear, which was similar for the tinnitus and no-tinnitus groups and which recovered partially over 6 months post-exposure
There was a considerable recovery of the ABR thresholds at 6 months following acoustic trauma (Figures 1A,B, right panel), pairwise comparisons revealed a significant difference between the ABR thresholds before and immediately after acoustic trauma (P = 0.0001), immediately and at 6 months after acoustic trauma (P = 0.0001) as well as before and at 6 months after acoustic trauma (P = 0.0001)
Summary
Tinnitus is the perception and conscious awareness of sound that is not physically present. These phantom sounds can be ringing or buzzing noises or sometimes hissing, grinding, or roaring. Many people experience tinnitus transiently at some time in their life, but for chronic tinnitus sufferers, the condition can be frustrating and debilitating. In severe cases, it can be extremely disturbing, and even lead to suicide [1]. Tinnitus affects 25% of the American population at some stage in their life, with 8% of people experiencing persistent or chronic tinnitus [1]. While the prevalence of chronic tinnitus normally increases with age, it is alarming that an increasing number of adolescents and young adults are experiencing it due to risky music-listening behaviors, such as prolonged exposure to high-volume music by using portable music players, or going to excessively loud nightclubs or attending pop/rock concerts [2]
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