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stimulation with levels of 40 and 70 dB (SPL) of rippled noise. Data were realigned and normalized to a custom made template using SPM5. First level analysis was performed using multiple regression and regions of interest (ROI) of the auditory pathway were defined (cortex, MGB, IC, SOC and CN). Percent signal changes were obtained for each condition for each region and symmetry indices were obtained. A second level analysis was performed using an ANOVA design to assess group differences and group-by-level interactions. Results from the ROI analysis indicate that for the control group the cortex and inferior colliculus respon- ded strongest to contralateral stimuli. A difference was observed between the two tinnitus patient groups. The left sided tinnitus group showed a predominant response towards ipsilateral stimuli at the cortex while the right sided tinnitus group responded more like the control group. A general trend of higher activation in the inferior colliculus as response to stimuli was observed in tinnitus patients compared to controls. Our data suggest that there are differences in activation on cortex level and inferior colliculus level bet- ween the control group and the patient groups. Analysis of other nuclei will be performed.

Differential Expression of HCN Channels in the Cochlear Nucleus. (Abstract of ARO Meeting Denver, Colorado) Ana Caban Cardona, Rebecca Eernisse, Paul Popper, David Friedland Medical College of Wisconsin

Hyperpolarization-activated currents (Ih) have been identified in many auditory brain stem neurons inclu- ding octopus and bushy cells. The channels responsible for these currents are hyperpolarization-activa- ted cyclic nucleotide-gated potassium channels of which four isoforms are known (i.e., HCN1-4). These channels influence resting membrane potentials, regulate neuronal excitability and likely play important roles in auditory signal processing. We used real-time RT-PCR and immunohistochemistry to investigate differential expression of all four HCN channels among the subdivisions of the cochlear nucleus. Higher levels of HCN2 and HCN4 mRNA were detected in the ventral subdivisions of the cochlear nucleus than in the DCN, although this did not reach statistical significance. Real-time RT-PCR results for HCN1 and HCN3, in contrast, showed no differential expression. We found immunostaining for HCN2 and HCN4 in the DCN but no staining in this region for the other two channels. Our HCN2 labeling was predominantly found in cartwheel cells although previous reports have also shown HCN2 in fusiform cells. We found HCN4 to be most highly expressed in the fusiform cells. HCN4 was also noted among large neurons within the auditory nerve root. We found no neuronal staining for HCN3 in any subdivision and all HCN3 staining appeared localized to fibers in the peri-neuronal spaces. Similar to other studies, we found strong HCN1 staining on octopus cells of the PVCN but in contrast to other studies we did not iden- tify significant staining in bushy cell regions. This study adds to the increasing evidence for differential expression among auditory neurons of the various hyperpolarization-activating potassium channels. The particular expression of HCN2 and HCN4, which are strongly regulated by cAMP, in the DCN may under- lie some forms of neuronal plasticity such as that associated with noise-induced DCN hyperactivity and the generation of tinnitus (Supported by NIH/NIDCD K08DC006227).

Differential gene expression profiles in salicylate ototoxicity of the mouse. (Abstract of ARO Meeting Denver, Colorado) Gi Jung IM1, Seo Jin Kim2, Sung Won Chae1, Jae Hoon Cho1, Hak Hyun Jung1,2 1Department of Otolaryngology, Korea University College of Medicine, SEOUL, KOREA, 2Department of Biomedical Sciences, Korea University, SEOUL, KOREA

Conclusion: This study demonstrated differential gene expression profiles in salicylate ototoxicity with

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