Elevated Fusiform Cell Activity in the Dorsal Cochlear Nucleus of Chinchillas with Psychophysical Evidence of Tinnitus

Abstract

Chinchillas with psychophysical evidence of chronic tinnitus were shown to have significantly elevated spontaneous activity and stimulus-evoked responses in putative fusiform cells of the dorsal cochlear nuclei (DCN). Chinchillas were psychophysically trained and tested before and after exposure to a traumatic unilateral 80 dB (sound pressure level) 4 kHz tone. Before exposure, two groups were matched in terms of auditory discrimination performance (noise, and 1, 4, 6, and 10 kHz tones). After exposure, a single psychophysical difference emerged between groups. The exposed group displayed enhanced discrimination of 1 kHz tones ( p ϭ 0.00027). Postexposure discrimination of other stimuli was unaffected. It was hypothesized that exposed animals experienced a chronic subjective tone (i.e., tinnitus), resulting from their trauma, and that features of this subjective tone were similar enough to 1 kHz to affect discrimination of 1 kHz objective signals. After psychophysical testing, single-unit recordings were obtained from each animal's DCN fusiform cell layer. Putative fusiform cells of exposed animals showed significantly ( p ϭ 0.0136) elevated spontaneous activity, compared with cells of unexposed animals. Putative fusiform cells of exposed animals showed a greater stimulus-evoked response to tones at 1 kHz ( p ϭ 0.0000006) and at characteristic-frequency ( p ϭ 0.0000009). This increased activity was more pronounced on the exposed side. No increase in stimulus-evoked responses was observed to other frequencies or noise. These parallel psychophysical and electrophysiological results are consistent with the hypothesis that chronic tonal tinnitus is associated with, and may result from, trauma-induced elevation of activity of DCN fusiform cells.

The role of central nervous system plasticity in tinnitus

“…These have been effectively used to compare both brain activity with tinnitus perceptions (e.g. Brozoski, Bauer, & Caspary, 2002), and constitute a powerful tool for exploring brain function and tinnitus, as well as interventional procedures.…”

Brainstem Auditory Evoked Potentials Suggest a Role for the Ventral Cochlear Nucleus in Tinnitus

“…In fact, it is entirely possible that multiple cochlear nucleus cell populations play a role in tinnitus, both VCN populations and, as indicated by a large body of animal work, DCN populations (Brozoski et al 2002;Kaltenbach et al 2004). It is also possible that the cochlear nucleus neuronal populations involved in tinnitus differ among people.…”

Deafness associated changes in expression of two-pore domain potassium channels in the rat cochlear nucleus

“…The responses of cochlear nucleus neurons to losing their dominant excitatory input may be to lower their threshold for activation through a downregulation of channels, which function to reduce excitability when they are active. If this is the case, the increase in neuronal excitability might be associated with the increased neuronal activity in the CN following complete or partial deafness found in central tinnitus (Brozoski et al, 2002;Imig and Durham, 2005;Kaltenbach et al, 2004;Zhang and Kaltenbach, 1998).…”