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The Effects of Salicylate on Auditory Evoked Potential Amplitudes from the Auditory Cortex and Brainstem Brian Sawka AuD Project Tinnitus Subjective tinnitus is the sensation of sound in the absence of an acoustic stimulus. Tinnitus can be induced by noise exposure (Axelsson & Hamernik, 1987; Job et al. 2007) ototoxic drugs (Huang & Schacht, 1989; Day et al. 1989) Tinnitus is usually associated with cochlear damage (Demeester et al. 2007; Job et al. 2007). Salicylate Causes Hearing Loss and Tinnitus Salicylate causes temporary hearing loss and tinnitus in humans (Hicks & Bacon, 1999; Halla et al. 1991). Tinnitus-like behaviors suggest that animals experience tinnitus with treatment of salicylate (Bauer et al. 1999; Jastreboff et al. 1988; Lobarinas et al. 2004; Yang et al, 2007). Consequently, tinnitus has been extensively used in research to study tinnitus Salicylate Enhances Auditory Evoked Potential Amplitude at the Auditory Cortex 2.0 Nomalized AC Amp Yang et. al (2007) showed enhancement of auditory cortex (AC) response amplitude with high intensity 16 and 20 kHz tone burst stimuli post salicylate treatment These frequencies were associated with tinnitus-like behavior in another set of animals (Yang et al. 2007) Amplitude in mV Pre SS-1h 1.5 1.0 0.5 0.0 30 50 70 dB SPL Time in ms Lu et al. (2008) 90 110 Cochlear/8th nerve, Cochlear Nucleus, and Inferior Colliculus I/O Functions Pre and Post Noise Exposure Salvi et al. found enhancement at the inferior colliculus with high level 1 kHz tone bursts post noise exposure using local implants in chinchillas (2000) Salvi et al. 2000 Aim of Study Observe if the enhancement of the AC waveform post salicylate is also present in the ABR waveform. To address this question, four implanted animals will be tested pre and post salicylate treatment for both: AC response ABR response Cochlea 8th Cochlear Nucleus Inferior Colliculus Auditory Cortex Methods: Subjects Subjects: Four male Sprague Dawley rats Implanted at 2-3 months of age Tested at 6-7 months of age Implants consist of: Auditory Cortex electrode (right side) Frontal lobe skull electrode Screw for head restraint Affixed to skull with dental cement and stainless steel screws The implant procedure has been described in detail (Yang et al, 2007; Lobarinas et al, 2006). Methods: Animal Restraint The rats were trained to remain still during awake recordings: Small modified plastic cage Head restraint using head screw and a mechanical arm Awake recordings: Required for AC recordings Chosen for ABR to avoid influences of anesthesia Methods: Auditory Stimuli 4 ms alternating polarity tone bursts of 4, 8, 12, 16 and 20 KHz Created in Tucker Davis Technologies (TDT) SigGen RP 4.4 software TDT Stimuli Hardware: Processor Attenuator Headphone driver 8 ohm tweeter ~ 2 ¼ inches from ear Left ear for AC recordings (contralateral to recording electrode) Right ear for ABR recordings (ispilateral to recording electrode) The auditory stimuli will be binaural as both ears will remain unrestricted Methods: Recording Hardware and Parameters TDT Recording hardware: Recording Software: TDT BioSig RP 4.41 BioSig and electrode settings for AC recording: Four channel head stage Medusa Preamp Medusa Base Station Recording electrode placed at the auditory cortex and reference at the frontal lobe of the skull (contralateral recording) Band pass filter 3 Hz - 1000 Hz and 60 Hz notch Stimulation rate 2/second and averaged 100 sweeps for each waveform. BioSig and electrode settings for ABR recording: Recording electrode placed at the skull and reference at the auditory cortex (ipsilateral recording) Band pass 100 Hz - 3000 Hz and 60 Hz notch Stimulation rate 19/second and averaged 512 sweeps for each waveform. Methods: Amplitude Measure for AC and ABR AC recordings Large positive peak ~ 11-15 ms Amplitude recorded peak to following trough in micro volts ABR recordings Positive peak ~ 4.5 - 5 ms (estimated latency of inferior colliculus) Amplitude recorded peak to following trough in micro volts Results: Auditory cortex response enhancement was observed for most conditions Auditory Cortex Amplitudes in Response to 20 KHz Tone Bursts for Animal 102607 Pre Salicylate 1 140 Pre Salicylate 2 2 hours post Salicy 1 day post Salicy 3 days post Salicy 100 80 60 40 20 Tone Burst Intensity in dB SPL 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 AC Amplitudes in Micro Volts 120 Results: Auditory Cortex Statistical Analysis Paired t test comparisons of pre and post salicylate AC amplitudes for all four animals: 4k: p = .047 8k: p = .0045 12k: p = .032 16k: p = .068 20k: p = .032 Alpha = .05 Micro Volts Across Animal Average for 20 KHz Auditory Cortex Amplitude at 90 dB SPL 120 100 Baseline 80 2 Hours Post Salicy 60 40 20 0 1 Results: ABR results for high intensity stimuli were typically smaller amplitude for 2 hours post salicylate compared to baseline Brainstem Responce Amplitudes in Response to 20 KHz Tone Bursts for Animal 102607 Pre Salicylate 1 2 Pre Salicylate 2 2 hours post Salicy 1.6 1 day post Salicy 3 days post Salicy 1.4 1.2 1 0.8 0.6 0.4 0.2 Tone Burst Intensity in dB SPL 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 ABR Amplitudes in Micro Volts 1.8 Results: ABR Statistical Analysis Paired t test comparisons of pre and post salicylate ABR amplitudes for all four animals: 4k: Missing data 8k: Missing data 12k: p = .001 16k: p = .061 20k: Missing data Alpha = .05 Micro Volts Across Animal Average for 12 KHz Brainstem Response Amplitude at 90 dB SPL 4 3.5 3 Baseline 2.5 2 Hours Post Salicy 2 1.5 1 0.5 0 1 Conclusions The AC results confirm high intensity tone burst enhancement post salicylate treatment The ABR data suggests that the amplitudes are overall decreased post salicylate at the inferior colliculus Discussion: Comparison of Results Salvi et al. studies using noise exposure Cochlea 8th Cochlear Nucleus Inferior Colliculus Auditory Cortex Current observations for salicylate treatment Cochlea 8th Cochlear Nucleus Inferior Colliculus Auditory Cortex Discussion This study is useful as a small pilot study The results suggest that hearing damage and tinnitus from salicylate may have a different physiological mechanism than noise exposure. A follow up study is recommended that would use local inferior collicului implants to verify these results. Recognition I would like to thank my research committee for their advisement and assistance for this project: Wei Sun, Ph.D Richard Salvi, Ph.D Joan Sussman, Ph.D Special thanks to: Lu Jianzhong, Ph.D References Axelsson, A. & Hamernik, R.P. (1987). Acute acoustic trauma. Acta Otolaryngol, 104, 225-233. Bauer, C.A., Brozoski, T.J., Rojas, R., Boley, J. & Wyder, M. (1999). Behavioral model of chronic tinnitus in rats. Otolaryngol Head Neck Surg, 121, 457-462. Day, R.O., Graham, G.G., Bjeri, D., Brown, M., Cairns, D., Harris, G., Hounsell, J., Platt-Hepworth, S., Reeve, R., Sambrook, P.N., et al. (1989). Concentration-response relationships for salicylate-induced ototoxicity in normal volunteers. Br J Clin Pharmacol, 28, 695-702. Demeester, K., Van Wieringen, A., Hendrickx, J.J., Topsakal, V., Fransen, E., Van Laer, L., De Ridder, D., Van Camp, G. & Van de Heyning, P. (2007). Prevalance of tinnitus and audiometric shape. Belgium ENT, 3(7), 37-49. Halla, J.T., Atchinson, S.L. & Hardin, J.G. (1991). Symptomatic salicylate ototoxicity: A useful indicator of serum salicylate concentration? Ann Rheum Dis, 50, 682-684. Hicks, M.L. & Bacon, S.P. (1999). Effects of aspirin on psychophysical measures of frequency selectivity, two-tone suppression, and growth of masking. J Acoust Soc Am, 106, 1436-1451. Huang, M.Y. & Schacht, J. (1989). Drug-induced ototoxicity, pathogenesis and prevention. Med Toxicol Adverse Drug Exp, 4(6), 452-67. References Huang, M.Y. & Schacht, J. (1989). Drug-induced ototoxicity, pathogenesis and prevention. Med Toxicol Adverse Drug Exp, 4(6), 45267. Jastreboff, P.J., Brennan, J.F., Coleman, J.K. & Sasaki, C.T. (1988). Phantom auditory sensation in rats: an animal model for tinnitus. Behav Neurosci, 102, 811-822. Job, A., Raynal, M. & Kosowski, M. (2007). Susceptibility to tinnitus revealed at 2 KHz range by bilateral lower DPOAEs in normal hearing subjects with noise exposure. Audiol Neurootol, 12(3), 137-44. Lu, J., Laundrie, E., Stoltzburg, D., Sun, W., Salvi, R. (2008). Abstract, Association for Research of Otolaryngology. Phoenix, AZ. Lobarinas, E., Sun, W., Cushing, R. & Salvi, R. (2004). A novel behavioral paradigm for assessing tinnitus using schedule-induced polydipsia avoidance conditioning (SIP-AC). Hear Res, 190 (1-2), 109-14. Salvi, R. J., Wang, J. & Ding, D. (2000). Auditory plasticity and hyperactivity following cochlear damage. Hear Res, 147, 261-274. Yang, G., Lobarinas, E., Zhang, L., Turner, J., Stolzberg, D., Salvi, R. & Sun, W. (2007). Salicylate induced tinnitus: Behavioral measures and neural activity in auditory cortex of awake rats. Hear Res, 226, 244-253.