AI Article Synopsis

  • Chronic tinnitus currently lacks effective treatments, but identifying specific markers could help develop therapeutics, with recent studies suggesting glutamatergic blockade in the cerebellar paraflocculus may reduce symptoms.
  • In an experiment, the NMDA antagonist D-AP5 was infused into rats with noise-induced tinnitus, resulting in significant reduction of tinnitus symptoms within three days and lasting effects observed for 23 days post-treatment.
  • Neural activity assessments showed that D-AP5 treatment led to decreased activity in regions associated with tinnitus, indicating that NMDA-mediated glutamatergic transmission in the paraflocculus is crucial for chronic tinnitus in this rat model.

Article Abstract

Chronic tinnitus has no broadly effective treatment. Identification of specific markers for tinnitus should facilitate the development of effective therapeutics. Recently it was shown that glutamatergic blockade in the cerebellar paraflocculus, using an antagonist cocktail was successful in reducing chronic tinnitus. The present experiment examined the effect of selective N-methyl d-aspartate (NMDA) receptor blockade on tinnitus and associated spontaneous brain activity in a rat model. The NMDA antagonist, D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) (0.5 mM), was continuously infused for 2 weeks directly to the ipsilateral paraflocculus of rats with tinnitus induced months prior by unilateral noise exposure. Treated rats were compared to untreated normal controls without tinnitus, and to untreated positive controls with tinnitus. D-AP5 significantly decreased tinnitus within three days of beginning treatment, and continued to significantly reduce tinnitus throughout the course of treatment and for 23 days thereafter, at which time testing was halted. At the conclusion of psychophysical testing, neural activity was assessed using manganese enhanced magnetic resonance imaging (MEMRI). In agreement with previous research, untreated animals with chronic tinnitus showed significantly elevated bilateral activity in their paraflocculus and brainstem cochlear nuclei, but not in mid or forebrain structures. In contrast, D-AP5-treated-tinnitus animals showed significantly less bilateral parafloccular and dorsal cochlear nucleus activity, as well as significantly less contralateral ventral cochlear nucleus activity. It was concluded that NMDA-mediated glutamatergic transmission in the paraflocculus appears to be a necessary component of chronic noise-induced tinnitus in a rat model. Additionally, it was confirmed that in this model, elevated spontaneous activity in the cerebellar paraflocculus and auditory brainstem is associated with tinnitus.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3834860PMC
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0077674PLOS

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