ANIMAL BEHAVIORAL MODELS OF TINNITUS

Transcription

1 JOURNAL OF OTOLOGY ANIMAL BEHAVIORAL MODELS OF TINNITUS ZHANG Chao, WANG Qiuju, SUN Wei Abstract The pathophysiology of tinnitus is poorly understood and treatments are often unsuccessful. A number of animal models have been developed in order to gain a better understanding of tinnitus. A great deal has been learned from these models regarding the electrophysiological and neuroanatomical correlates of tinnitus following exposure to noise or ototoxic drugs. Reliable behavioral data is important for determining whether such electrophysiological or neuroanatomical changes are indeed related to tinnitus. Of the many documented tinnitus animal behavioral paradigms, the acoustic startle reflex had been proposed as a simple method to identify the presence or absence of tinnitus. Several behavioral models based on conditioned response suppression paradigms have also been developed. In addition to determining the presence or absence of tinnitus, some of the behavioral paradigms have provided signs of the onset, frequency, and intensity of tinnitus in animals. Although none of these behavioral models have been proved to be a perfect model, these studies provide useful information on understanding the neural mechanisms underlying tinnitus. Key word: Tinnitus; Behavioral model; Acoustic startle; Noise exposure; Salicylate Tinnitus is a symptom of many pathological conditions and is an auditory phantom sensation experienced when no external sound is present. Tinnitus occurs with a surprisingly high prevalence affecting about 35% of the general population, with 10%-15% of individuals experiencing prolonged tinnitus requiring medical evaluation [1-3]. For 10% of the population tinnitus has a significant impact on their quality of life [4]. Over the years, progress has been made using electrophysiology, cell biology, molecular biology, and other techniques to understand the neural correlates of tinnitus. A number of methods have been used to reduce the symptoms of tinnitus, including auditory masking procedures [5-9], electrical stimulation [10-14], and pharmacological treatments [1, 15-20]. The phantom perception of tinnitus often begins with the onset of hearing loss induced by acoustic overstimulation [21-25] or ototoxic drugs [23, 24, 26, 27]. However, the exact causes of tinnitus remain largely unclear. A number of interesting neurophysiological changes have been identified regarding tinnitus in animal models. For example, an increase in neuronal spike synchrony has been observed in auditory cortex and is thought to be related to tinnitus [28]. Additionally, an increase in spontaneous firing rates in the auditory cortex and inferior colliculus has also been associated with tinnitu s[29, 30] [28, 31-36]. However, whether or not these changes are truly related to tinnitus cannot be confirmed unless a behavioral testing is used to evaluate the presence or absence of tinnitus. Therefore, it is important to employ behavioral techniques that permit tinnitus to be assessed in individual animals treated with a particular tinnitus inducing agent in order to determine if tinnitus is present or absent at a particular time [36-41]. Because tinnitus is subjective in nature and there is no objective test of tinnitus, it can therefore be difficult to quantify in an animal model. Currently, there are several useful animal behavioral models that Affiliation: 1 Department of Otolaryngology, Chinese PLA General Hospital, 28 Fuxing Road, Beijing, , P.R. China 2 Center for Hearing & Deafness, Department of Communicative Disorders and Sciences, State University of New York at Buffalo, 3435 Main Street, Buffalo, NY Corresponding authors: SUN Wei and WANG Qiuju SUN Wei, weisun@buffalo.edu WANG Qiuju, wqcr301@sina.com 58

2 use animal behavioral changes which may associate with tinnitus to study the underlying neural mechanisms and potential treatments of tinnitus. Tinnitus model based on acoustic startle reflex paradigm In recent years, the acoustic startle reflex (ASR) became a popular technique for tinnitus assessment [36, 42]. This behavioral model confers a significant advantage than the time-consuming behavioral approaches utilizing basic mechanisms of conditioning [37, 38, 40, 42-46]. During the test, animals were placed in a holder on top of a piezo-electric transducer that measures the animal s motoric reflex to a sudden loud sound (Figure 1A). The technique relies on a reduction of the ASR by a preceding silent gap in an otherwise constant acoustic background (Figure 1B). An animal is presumed to have tinnitus if a preceding gap fails to reduce the startle reflex due to tinnitus filling in the silent gap (Figure 1C-D). This method has been described and used in a number of studies [45] [42, 47]. Prepulse inhibition of the ASR has been used to assess tinnitus in different laboratory animals. This technique doesn t require complex behavioral manipulations (food or water deprivation, finely tuned shock parameters, variable reinforcement schedules, etc.) and also doesn t require long durations to train the animals. Additionally, ASR does not rely on learning, memory or motivation. The startle neural circuit, its modulation using background sounds, and stimulus parameters has been studied extensively [42, 48-53]. It s easy for newcomers learning to correctly apply gap detection techniques for tinnitus assessment in different animals. This method has been used to assess tinnitus induced by ototoxic drugs or acoustic trauma in mice [54, 55] and rats [36, 42, 56-58]. Although prepulse inhibition of the ASR seems to be an efficient and reliable method, a number of questions have arisen regarding the use of the paradigm in behavioral models of tinnitus. One question is whether changes in prepulse inhibition are due to tinnitus or simply due the hearing loss. A number of studies have demonstrated a reduction in startle amplitude following use of noise exposure to induce tinnitus suggesting that hearing loss Figure 1. (A) Animals are placed in a holder on top of a piezo-electric transducer. (B) Acoustic startle reflex with constant acoustic background. (C) Reduction of the acoustic startle reflex by a preceding silent gap in an otherwise constant acoustic background. (D) Tinnitus filling in the gap, no reduction of the acoustic startle reflex by a preceding silent gap in constant acoustic background. 59

3 may alter startle amplitude [54, 59]. Additionally, if a subject s tinnitus is not restricted to a particular frequency band or is not a simple stimulus such as a broadband noise, it would be difficult to evaluate tinnitus using this approach. These issues need to be addressed for validating this model for tinnitus detection. Tinnitus from noise exposure and ototoxic drugs often lead to sound-evoked hyperactivity along the auditory pathway, particularly at the auditory cortex, as well as behavioral evidence of hyperactivity [47, 60, 61]. High-doses of salicylate, which reliably induce tinnitus, also induces functional changes in the central auditory system [36, 47]. Salicylate has been shown to disrupt GABAergic (inhibitory) synaptic transmission in the inferior colliculus [62]. In order to study this auditory phantom sensation and neurophysiological changes, a behavioral test that reflects the auditory pathway is needed. Recent animal behavioral techniques are based on conditioned response suppression. Sugar water [46], food pellets [43] and water [63] have been used as reward in these conditioning paradigms. In the Jastreboff s model, animals are trained to lick for water during periods of sound (safe-to-drink condition) and to stop licking during periods of silence using a mild foot shock (Figure 2). After training to criterion performance, a tinnitus-inducing injection of salicylate was given to the experimental group of rats. Licking suppression was measured over 5-10 days until the behavioral response extinguished due to the removal of the shock. Licking suppression extinguished more rapidly in the experimental group than in the control group, with the salicylate-treated group licking more than control animals during silent periods. This suggests that they were hearing a sound when no external sound was being presented and has been interpreted as the presence of tinnitus [64]. Some studies had tried to estimate the pitch of an animal s tinnitus using a behavioral paradigm. Jestreboff et al. used specific auditory stimulation in place of the salicylate injections. Twelve rats were assigned to one of two treatment groups and received the same water deprivation and weight monitoring regimen. Animals were trained to lick for water during periods of sound (safe-to-drink condition) and to stop licking during periods of silence using a mild foot shock. They still received continuous 24 hr tonal presentations of 7 khz, 60 db SPL superimposed on the background noise. There was no significant difference between three groups of animal results. A sound at 7 khz and 60 db SPL is used to simulate the sound of tinnitus induced by sodium salicylate. This study used a sound simulation method and they found the pitch of tinnitus induced by high doses of salicylate may be closed to 7 khz. Behavioral model based on conditioned response suppression 60 Figure 2. Animals are trained to lick for water during periods of sound (safe-to-drink condition) and to stop licking during periods of silence using a mild foot shock. Figure 3. Animals were trained to move into or stay in the light side of a two compartment shuttle box when the frequency of a continuously played background sound was 4 khz, and to cross to the dark side when the frequency of the sound was 3 khz. Shuttle box paradigm Another study combined behavioral estimations of tinnitus pitch with electrophysiological recording. They found that hearing lesions produced a tinnitus pitch in the hearing-loss frequency range and auditory cortex also showed different sound representations in low and

4 high characteristic frequency areas [65]. In this study, animals were trained to move into or stay in the light side of a two compartment shuttle box when the frequency of a continuously played background sound was 4 khz, and to cross to the dark side when the frequency of the sound was 3 khz (Figure 3). Animals were trained to reach the criterion so that they correctly shuttled between compartments 70% of the time for 3 consecutive days. After training, silent probe trials were inserted in which no foot shock was delivered to the animals. Animals generally preferred the dark side during the silent probe trials. Next, a high-frequency hearing loss was induced in the adult rats by exposing them to a 4-kHz tone at 123 db for 7 h. After the hearing lesion, rats consistently increased their preference for the high-pitched compartment (i.e., the light side) in the silent probe trials. The preference for the high-pitch compartment in the absence of external sounds indicates that they perceived tinnitus in the hearing-loss frequency range. The schedule induced polydipsia avoidance conditioning (SIPAC) paradigm The SIPAC model is designed based on Jestreboff s model to increase the testing window [40]. Food restricted rats were self-trained to lick for water during the time between scheduled deliveries of food pellets. Rats were allowed to lick during quiet periods but will be trained not licking under sound stimulus condition. After training to a criterion in which licks-in-quiet (correct response) exceeded 90% of the total licks, rats were treated with saline and four different doses of salicylate [40]. Results demonstrate that rats treated with high doses of salicylate reduce their number of licks in quiet, behavior indicating that they hear a phantom sound (i.e. tinnitus) during the silent periods. The SIPAC procedure represents a reliable new method for assessing tinnitus in animals. This paradigm has also previously been combined with the startle reflex paradigm in which rodents were tested on both paradigms for the presence of tinnitus [36]. In this study, the pitch of the tinnitus was found to be near 16 khz after treatment with salicylate. Electrophysiological recordings from chronically implanted multichannel electrode arrays were also used in this study to monitor the local field potentials and spontaneous discharge rates from multiunit clusters in the auditory cortex of awake rats. Psychophysical model of tinnitus Bauer et al. developed a tinnitus animal model to reflect several features of tinnitus observed in humans. Rats were trained to press a lever during background noise to obtain food and to stop pressing the lever during silent intervals to avoid a foot shock [66]. Tinnitus was measured using a psychophysical procedure, which required the animals to discriminate between auditory test stimuli consisting of tones, noise, and 0 db. After noise exposure, the animals were continuously tested for 17 months by a procedure where four intervals containing a tone without shocks were presented, followed by four silent intervals where a shock was administered if the animal did not stop lever pressing. They found that the noise exposed animals had tonal tinnitus and the control animals did not have tinnitus. The tinnitus was found to persist and intensify over 17 months. This paradigm was also compared with the startle reflex paradigm and both paradigms showed consistent results in noise exposure induced tinnitus [42]. Possible mechanisms underlying tinnitus Hearing loss not only affects the cochlea, but also has significant effects on the central nervous system reinforcing the idea that hearing involves many different regions of the brain [47]. Noise-induced cochlear damage has a significant effect on cell proliferation and neurogenesis in the hippocampus [67]. Eggermont et al. found that noise-induced hearing loss followed by a few weeks of recovery in quiet caused reorganization of the tonotopic map in cat s primary auditory cortex [68]. The changes in spontaneous firing rates and in neural synchrony were nearly the same after a few hours and after a few weeks but tonotopic map changes developed slowly over time. It has been proposed that these changes may be a neural substrate for tinnitus. A stable and reliable animal behavioral paradigm is the key factor in studies of tinnitus in animals. Today most of the established tinnitus animal models are based on clinical manifestation of tinnitus in humans. Methods which induce tinnitus in humans, such as ototoxic drugs and noise exposure, are also used to induce tinnitus in animals. Although human patients are able to communicate features of their tinnitus such as intensity, duration, and frequency, these features are not always easy to determine in animals models. We need to design a stable, reliable and clear animal behavioral model in order to obtain information about tinnitus generation, intensity, duration and frequency in animals. Clearly, more work needs to be done in order to establish a well validated tinnitus animal model in order to reveal the underlying mechanisms and to establish a potential therapeutic treatment for tinnitus. Acknowledgement The authors greatly appreciate the help from Ms. Sar- 61

5 ah Hayes who edited the paper. This work was supported by the grants of the National Key Basic Research Program of China, No.2014CB943001, the National Natural Science Foundation of China, Major Project, No References [1] Coles, R.R. and R.S. Hallam, Tinnitus and its management. Br Med Bull, (4): p [2] Heller, A.J., Classification and epidemiology of tinnitus. Otolaryngol Clin North Am, (2): p [3] Shargorodsky, J., G.C. Curhan, and W.R. Farwell, Prevalence and characteristics of tinnitus among US adults. Am J Med, (8): p [4] Cooper, J.C., Jr., Health and Nutrition Examination Survey of : Part II. Tinnitus, subjective hearing loss, and well-being. J Am Acad Audiol, (1): p [5] Hazell, J.W. and S. Wood, Tinnitus masking-a significant contribution to tinnitus management. Br J Audiol, (4): p [6] Hazell, J.W., et al., A clinical study of tinnitus maskers. Br J Audiol, (2): p [7] McNeill, C., et al., Tinnitus pitch, masking, and the effectiveness of hearing aids for tinnitus therapy. Int J Audiol, (12): p [8] Oz, I., et al., Effectiveness of the combined hearing and masking devices on the severity and perception of tinnitus: a randomized, controlled, double-blind study. ORL J Otorhinolaryngol Relat Spec, (4): p [9] Vernon, J.A. and M.B. Meikle, Masking devices and alprazolam treatment for tinnitus. Otolaryngol Clin North Am, (2): p , vii. [10] Battmer, R.D., R. Heermann, and R. Laszig, [Suppression of tinnitus by electric stimulation in cochlear implant patients]. HNO, (4): p [11] Hazell, J.W., L.J. Meerton, and M.J. Conway, Electrical tinnitus suppression (ETS) with a single channel cochlear implant. J Laryngol Otol Suppl, : p [12] Kuk, F.K., et al., Alternating current at the eardrum for tinnitus reduction. J Speech Hear Res, (2): p [13] Lee, S.K., et al., Effectiveness of transcutaneous electrical stimulation for chronic tinnitus. Acta Otolaryngol, [14] Punte, A.K., D. De Ridder, and P. Van de Heyning, On the necessity of full length electrical cochlear stimulation to suppress severe tinnitus in single-sided deafness. Hear Res, : p [15] Davies, E. and I. Donaldson, Tinnitus, membrane stabilizers and taurine. Practitioner, (1456 ( Pt 2)): p [16] DeBartolo, H.M., Jr., Zinc and diet for tinnitus. Am J Otol, (3): p [17] Langguth, B. and A.B. Elgoyhen, Current pharmacological treatments for tinnitus. Expert Opin Pharmacother, (17): p [18] Marks, N.J., H. Karl, and C. Onisiphorou, A controlled trial of hypnotherapy in tinnitus. Clin Otolaryngol Allied Sci, (1): p [19] Patterson, M.B. and B.J. Balough, Review of pharmacological therapy for tinnitus. Int Tinnitus J, (2): p [20] Vermeij, P. and J.H. Hulshof, Dose finding of tocainide in the Vol.9 No.2 treatment of tinnitus. Int J Clin Pharmacol Ther Toxicol, (4): p [21] Atherley, G.R., T.I. Hempstock, and W.G. Noble, Study of tinnitus induced temporarily by noise. J Acoust Soc Am, (6): p [22] Axelsson, A. and R.P. Hamernik, Acute acoustic trauma. Acta Otolaryngol, (3-4): p [23] Eggermont, J.J., Hearing loss, hyperacusis, or tinnitus: what is modeled in animal research? Hear Res, : p [24] Kaltenbach, J.A., Tinnitus: Models and mechanisms. Hear Res, (1-2): p [25] Loeb, W.J. and E.E. Smith, Airway obstruction in a newborn by pedunculated pharyngeal dermoid. Pediatrics, (1): p [26] Gerharz, E.W., et al., Neomycin-induced perception deafness following bladder irrigation in patients with end-stage renal disease. Br J Urol, (4): p [27] Kopelman, J., et al., Ototoxicity of high-dose cisplatin by bolus administration in patients with advanced cancers and normal hearing. Laryngoscope, (8 Pt 1): p [28] Ochi, K. and J.J. Eggermont, Effects of salicylate on neural activity in cat primary auditory cortex. Hear Res, (1-2): p [29] Basta, D. and A. Ernst, Effects of salicylate on spontaneous activity in inferior colliculus brain slices. Neurosci Res, (2): p [30] Chen, G.D. and P.J. Jastreboff, Salicylate-induced abnormal activity in the inferior colliculus of rats. Hear Res, (2): p [31] Gaese, B.H. and J. Ostwald, Anesthesia changes frequency tuning of neurons in the rat primary auditory cortex. J Neurophysiol, (2): p [32] Jastreboff, P.J. and C.T. Sasaki, Salicylate-induced changes in spontaneous activity of single units in the inferior colliculus of the guinea pig. J Acoust Soc Am, (5): p [33] Ma, W.L., H. Hidaka, and B.J. May, Spontaneous activity in the inferior colliculus of CBA/J mice after manipulations that induce tinnitus. Hear Res, (1-2): p [34] Niu, Y., et al., Hyperexcitability of inferior colliculus neurons caused by acute noise exposure. J Neurosci Res, (2): p [35] Thomma, B.P., et al., Separate jasmonate-dependent and salicylate-dependent defense-response pathways in Arabidopsis are essential for resistance to distinct microbial pathogens. Proc Natl Acad Sci U S A, (25): p [36] Yang, G., et al., Salicylate induced tinnitus: behavioral measures and neural activity in auditory cortex of awake rats. Hear Res, (1-2): p [37] Guitton, M.J., et al., Salicylate induces tinnitus through activation of cochlear NMDA receptors. J Neurosci, (9): p [38] Heffner, H.E. and I.A. Harrington, Tinnitus in hamsters following exposure to intense sound. Hear Res, (1-2): p [39] Kaltenbach, J.A., et al., Cisplatin-induced hyperactivity in the dorsal cochlear nucleus and its relation to outer hair cell loss: relevance to tinnitus. J Neurophysiol, (2): p [40] Lobarinas, E., et al., A novel behavioral paradigm for assessing tinnitus using schedule-induced polydipsia avoidance conditioning (SIP-AC). Hear Res, (1-2): p

6 [41] Rachel, J.D., J.A. Kaltenbach, and J. Janisse, Increases in spontaneous neural activity in the hamster dorsal cochlear nucleus following cisplatin treatment: a possible basis for cisplatin-induced tinnitus. Hear Res, (1-2): p [42] Turner, J.G., et al., Gap detection deficits in rats with tinnitus: a potential novel screening tool. Behav Neurosci, (1): p [43] Bauer, C.A., et al., Behavioral model of chronic tinnitus in rats. Otolaryngol Head Neck Surg, (4): p [44] Heffner, H.E. and G. Koay, Tinnitus and hearing loss in hamsters (Mesocricetus auratus) exposed to loud sound. Behav Neurosci, (3): p [45] Longenecker, R.J. and A.V. Galazyuk, Methodological optimization of tinnitus assessment using prepulse inhibition of the acoustic startle reflex. Brain Res, : p [46] Ruttiger, L., et al., A behavioral paradigm to judge acute sodium salicylate-induced sound experience in rats: a new approach for an animal model on tinnitus. Hear Res, (1-2): p [47] Sun, W., et al., Salicylate increases the gain of the central auditory system. Neuroscience, (1): p [48] Barsz, K., et al., Behavioral and neural measures of auditory temporal acuity in aging humans and mice. Neurobiol Aging, (4): p [49] Carlson, S. and J.F. Willott, The behavioral salience of tones as indicated by prepulse inhibition of the startle response: relationship to hearing loss and central neural plasticity in C57BL/6J mice. Hear Res, (1-2): p [50] Hoffman, S., S. Kahn, and M. Seitchik, Late Problems in the Management of the Pierre Robin Syndrome. Plast Reconstr Surg, : p [51] Koch, M. and H.U. Schnitzler, The acoustic startle response in rats--circuits mediating evocation, inhibition and potentiation. Behav Brain Res, (1-2): p [52] Swerdlow, N.R., D.L. Braff, and M.A. Geyer, Cross-species studies of sensorimotor gating of the startle reflex. Ann N Y Acad Sci, : p [53] Swerdlow, N.R., M.A. Geyer, and D.L. Braff, Neural circuit regulation of prepulse inhibition of startle in the rat: current knowledge and future challenges. Psychopharmacology (Berl), (2-3): p [54] Longenecker, R.J. and A.V. Galazyuk, Development of tinnitus in CBA/CaJ mice following sound exposure. J Assoc Res Otolaryngol, (5): p [55] Middleton, J.W., et al., Mice with behavioral evidence of tinnitus exhibit dorsal cochlear nucleus hyperactivity because of decreased GABAergic inhibition. Proc Natl Acad Sci U S A, (18): p [56] Kraus, K.S., et al., Noise trauma impairs neurogenesis in the rat hippocampus. Neuroscience, (4): p [57] Wang, H., et al., Plasticity at glycinergic synapses in dorsal cochlear nucleus of rats with behavioral evidence of tinnitus. Neuroscience, (2): p [58] Zhang, J., Y. Zhang, and X. Zhang, Auditory cortex electrical stimulation suppresses tinnitus in rats. J Assoc Res Otolaryngol, (2): p [59] Lobarinas, E., S.H. Hayes, and B.L. Allman, The gap-startle paradigm for tinnitus screening in animal models: limitations and optimization. Hear Res, : p [60] Eggermont, J.J. and L.E. Roberts, The neuroscience of tinnitus. Trends Neurosci, (11): p [61] Roberts, L.E., et al., Ringing ears: the neuroscience of tinnitus. J Neurosci, (45): p [62] Wang, H.T., et al., Sodium salicylate suppresses serotonin-induced enhancement of GABAergic spontaneous inhibitory postsynaptic currents in rat inferior colliculus in vitro. Hear Res, (1-2): p [63] Jastreboff, P.J., J.F. Brennan, and C.T. Sasaki, An animal model for tinnitus. Laryngoscope, (3): p [64] Jastreboff, P.J., et al., Phantom auditory sensation in rats: an animal model for tinnitus. Behav Neurosci, (6): p [65] Yang, S., et al., Homeostatic plasticity drives tinnitus perception in an animal model. Proc Natl Acad Sci U S A, (36): p [66] Bauer, C.A. and T.J. Brozoski, Assessing tinnitus and prospective tinnitus therapeutics using a psychophysical animal model. J Assoc Res Otolaryngol, (1): p [67] Kraus, K.S., et al., Relationship between noise-induced hearing-loss, persistent tinnitus and growth-associated protein-43 expression in the rat cochlear nucleus: does synaptic plasticity in ventral cochlear nucleus suppress tinnitus? Neuroscience, : p [68]Eggermont, J.J., Cortical tonotopic map reorganization and its implications for treatment of tinnitus. Acta Otolaryngol Suppl, 2006(556): p (Received June 23, 2014 ) 63