Brain chemistry changes associated with the common hearing disorder, tinnitus.

What is it about?

Three important neurotransmitters, gamma-aminobutyric acid (GABA), glutamic acid (Glu), and acetyl choline Ach) (inferred from the surrogate indicator choline). were measured ex vivo in the brains of rats with and without evidence of chronic sound-induced tinnitus. A pattern of local increases and decreases was found in several areas of the auditory pathway, in animals with tinnitus.

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Why is it important?

These results were important because they show that more than one neurotransmitter is affected in the auditory system of animals with tinnitus. Prior experiments suggested that tinnitus animals would have decreased GABA activity, since GABA is primarily and inhibitory neurotransmitter, and concommitantly have elevated Glu, since Glu is primarily an excitatory neurotransmitter. Point localized proton magnetic resonance indicated that both elevated and decreased levels of GABA and Glu were found, depending upon pathway location. Interestingly levated Ach was found in the auditory cortiex, possibly reflecting alterations in attention. As expected, Glu levels were elevated in the auditory cortex of tinnitus animals, while GABA levels were also, unexpectedly elevated in the auditory cortex of tinnitus animals and non-tinnitus animals that had been exposded to loud sound.

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