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the onset and pitch of quinine-induced tinnitus in rats treated with different doses of quinine. A 50 ms silent gap (gap pre-pulse) in a continuous background noise was used to inhibit the startle reflex elicited by a high level noise burst. The gap was embedded in narrow band noises (NBN) with center frequen- cies at 6, 12, 16 or 24 kHz. Noise burst pre-pulse inhibition of acoustic startle (NBIAS) was also evaluated to monitor potential chan- ges in hearing following quinine. GPIAS results showed evidence of tinnitus like behavior at frequencies above 6 kHz with no changes in hearing threshold at doses of quinine up to 150 mg/kg. Tinnitus-like behaviors with GPIAS were consistent with previous SIP-AC data, strengthening the use of GPIAS as an animal model of tinnitus (Supported in part by Tinnitus Research Consortium).

Salicylate-induced tinnitus: effects of salicylate on neurons in dorsal cochlear nucleus. (Abstract of ARO Meeting Denver, Colorado) Lei Wei, Wei Sun, Dalian Ding, Matthew Xu-Friedman, Richard Salvi University at Buffalo

The neural mechanisms for tinnitus are not well understood, but one hypothesis is that it originates from high rates of spontaneous activity in the dorsal cochlear nucleus (DCN). Support for this hypothesis has come from studies showing elevated spontaneous rates in the DCN following noise and cisplatin-induced hearing loss. High doses of sodium salicylate reliably induce tinnitus, but it is unclear what effects sali- cylate has on spontaneous activity in the DCN. To test this hypothesis, we prepared brain slices of the DCN from p13-20 rats and recorded the spontaneous firing rate of individual neurons before, during and after treatment with 1.4 mM salicylate. This concentration of salicylate in CSF has been shown to induce behavioral manifestations of tinnitus in rats. Recordings were obtained from three cell types, fusiform, cartwheel and giant cells, with identifications based on their morphological and/or physiological characte- ristics. The spontaneous spike rate of cartwheel and giant cells remained unchanged or increased slightly after salicylate perfusion. In contrast, the spontaneous spike rate of most fusiform cells decreased significantly after salicylate treatment. The results indicate that the effects of salicylate are specific to fusiform cells. Spontaneous spike rate partially recovered following brief (3-5 min) salicylate perfusion and wash-out. The recovery of spontane- ous spike rate in fusiform cells was inversely related to perfusion duration and salicylate concentration. To determine if the decrease in spontaneous rate was induced by changes in synaptic activity, we recor- ded spontaneous post-synaptic currents in voltage clamp. No significant change was seen after salicyla- te treatment. These results suggest that the salicylate-induced decrease in spontaneous rate in fusiform cells is unlikely to be due a change in synaptic input, but may involve changes in the cell’s intrinsic properties (Supported in part by Tinnitus Research Consortium).

The sound of stress: blunted cortisol reactivity to psychosocial stress in tinnitus suffe- rers. Neurosci Lett. 2007 Jan 10;411(2):138-142. Hebert S, Lupien SJ Ecole d‘orthophonie et d‘audiologie, Universite de Montreal, Canada; Centre de recherche, Institut uni- versitaire de geriatrie de Montreal, Canada. sylvie.hebert@umontreal.ca

Clinical observations suggest that tinnitus is modulated by stress. However, there is little empirical data to support the link between stress and tinnitus. In this study, we measured the stress hormone cortisol to examine the reactivity of the hypothalamic-pituitary-adrenal (HPA) axis in tinnitus participants as well as in healthy controls without tinnitus. Eighteen participants with tinnitus and 18 controls without tinnitus were exposed to the Trier Social Stress Task and cortisol sampling and subjective ratings were obtained

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