Tinnitus

Tinnitus is described as a sensation of hearing sounds without any external source. This sensation can be similar to hear ringing, clicking, hissing or other sounds. Tinnitus can interfere with concentration and sleep and can cause Anxiety, depression and suicide attempt. Studies showed that the endocannabinoid system plays an important role in the development of tinnitus through the CB1 receptor and 2AG. THC and CBD can modulate tinnitus symptoms, however, the specific mechanism of cannabinoids remain unclear. Since the endocannabinoid system is involved in tinnitus development, studying the effects of cannabinoids on it can be helpful to find a future treatment for this disorder.

Receptors: 
Endocannabinoids: 
Phytocannabinoids: 
Literature Discussion: 

CB1 receptors and 2AG are expressed in the auditory brainsteam and their role may involve modulation of the balance of excitation and inhibition in auditory circuits  (Zhao et al., 2009). Also, the endocannabinoid system may play a role in multisensory integration in the brain (Zhao et al., 2011). The  development of tinnitus in rats may be related to a reduced number of CB1 receptors in the ventral cochlear nucleus (Zheng et al., 2007).

Studies with animals suggest that synthetic cannabinoid agonists or mixed administration of phytocannabinoids THC and CBD could exacerbate induced tinnitus symptoms (Zheng et al., 2010, 2015).

A recent review on the topic points out the relationship between the potential anti-epileptic effects of cannabinoids and their application to tinnitus (Smith and Zheng, 2015). More specific research on the role of CB1 receptor in the auditory brainsteam could help to find if there is any appropriate cannabinoid cocktail to treat this disease.

Literature:

Smith, P.F., and Zheng, Y. (2015). cannabinoids, cannabinoid receptors and tinnitus. Hear. Res. Zhao, Y., Rubio, M.E., and Tzounopoulos, T. (2009). Distinct functional and anatomical architecture of the endocannabinoid system in the auditory brainstem. J. Neurophysiol. 101, 2434–2446.

Zhao, Y., Rubio, M., and Tzounopoulos, T. (2011). Mechanisms underlying input-specific expression of endocannabinoid-mediated synaptic plasticity in the dorsal cochlear nucleus. Hear. Res. 279, 67–73.

Zhao, Y., Rubio, M.E., and Tzounopoulos, T. (2009). Distinct functional and anatomical architecture of the endocannabinoid system in the auditory brainstem. J. Neurophysiol. 101, 2434–2446.

Zheng, Y., Baek, J.-H., Smith, P.F., and Darlington, C.L. (2007). cannabinoid receptor down-regulation in the ventral cochlear nucleus in a salicylate model of tinnitus. Hear. Res. 228, 105–111.

Zheng, Y., Stiles, L., Hamilton, E., Smith, P.F., and Darlington, C.L. (2010). The effects of the synthetic cannabinoid receptor agonists, WIN55,212-2 and CP55,940, on salicylate-induced tinnitus in rats. Hear. Res. 268, 145–150.

Zheng, Y., Reid, P., and Smith, P.F. (2015). cannabinoid CB1 Receptor Agonists Do Not Decrease, but may Increase Acoustic Trauma-Induced Tinnitus in Rats. Front. Neurol. 6, 60.

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