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of salicylate application on the single unit spontaneous activity in brain slices of the cochlear nucleus, medial geniculate body and primary auditory cortex. Single unit responses were extracellularly recorded in 200 μm thick slices of the related deafferentiated brain area. During the measurement of spontaneous activity, 1.4 mM sodium salicylate (corresponding to tinnitus related serum levels in rats (Cazals, 2000, Prog. Neurobiol. 62, 583-631)) were added by super- fusion. Sixty seven percent of the neurons in the cochlear nucleus, 76 percent of the neurons in the medial ge- niculate body and 64 percent of the neurons in the primary auditory cortex responded with a significant and reversible change in firing rate during superfusion with salicylate. The mean value of absolute chan- ges in neuronal firing rate was significantly lower in the cochlear nucleus and primary auditory cortex than in the medial geniculate body. The response of neurons within the medial geniculate body was not significantly different to those obtained earlier from the inferior colliculus. The present data suggest that the auditory midbrain and thalamus plays a key role in the salicylate-indu- ced tinnitus generation (Supported by the Sonnenfeld Foundation, Berlin, Germany).

Effects of Sodium Salicylate Induced Tinnitus on Auditory Cortex Local Field Potentials in Awake Rats. (Abstract of ARO Meeting Denver, Colorado) Daniel Stolzberg1, Wei Sun1, Guang Yang2, Edward Lobarinas1, Richard Salvi1 1University at Buffalo, 2Yueyang Hospital of Shanghai Traditional Medical and Pharmacy University

Effects of Sodium Salicylate Induced Tinnitus on Auditory Cortex Local Field Potentials in Awake Rats Sodium salicylate (aspirin), a well known inducer of tinnitus in both humans and animals, has been used extensively to investigate the neurophysiological correlates of tinnitus in animal models. Despite the fact that tinnitus is only perceived when subjects are conscious, nearly all of the neurophysiological studies of tinnitus carried out to date have been carried out under anesthetics which disrupt or alter the neural pro- cess that give rise to this phantom auditory sensation. To avoid the confounding effects of anesthetics, we carried out a series of experiments in which we measured the tone-burst evoked, local field potential from the auditory cortex (AC) of conscious rats before and after administering a high dose (250 mg/kg, i.p.) of salicylate known to produce behavioral signs of tinnitus around 16 kHz. A chronic, electrode implanted on the AC was used to record the cortical evoked potential in response to tone bursts presen- ted at 4, 8, 12, 16, 24 and 32 kHz. Sound level was increased from the animal’s threshold up to 90 dB SPL. Preliminary recordings showed that salicylate caused an increase in the peak-to-peak amplitude of the AC evoked response at 2 h and 6 h post-treatment. The largest amplitude increase, on the order of 80%, occurred at 16 kHz around 90 dB SPL (p<0.05). The salicylate-induced amplitude enhancement was noticeably less at frequencies below 16 kHz (45-55%, 4-12 kHz) and above 16 kHz (35-55%, 24- 32 kHz). The AC amplitude enhancement was greatest at 2 h post-salicylate and decreased slightly at 6 h post-treatment, except at 16 kHz where there was a slight amplitude increases (Supported in part by grant from the Tinnitus Research Consortium).

Effects of somatosensory electrical stimulation on neural activity of the dorsal cochlear nucleus of hamsters. (Abstract of ARO Meeting Denver, Colorado) Jinsheng Zhang1,2, Zhenlong Guan1,3 1Department of Otolaryngology, Wayne State University School of Medicine, 2Department of Communica- tion Sciences & Disorders, Wayne State Univ College of Liberal Arts & Science, 3Department of Zoology, Hebei Normal University College of Life Sciences

It has been shown that sound exposure induces hyperactivity in the dorsal cochlear nucleus (DCN) in

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