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Tan HT, Smith PF, Zheng Y. Time-dependent effects of acoustic trauma and tinnitus on extracellular levels of amino acids in the inferior colliculus of rats. Hear Res 2024; 443:108948. [PMID: 38219615 DOI: 10.1016/j.heares.2024.108948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 12/19/2023] [Accepted: 01/02/2024] [Indexed: 01/16/2024]
Abstract
Chronic tinnitus is a debilitating condition with very few management options. Acoustic trauma that causes tinnitus has been shown to induce neuronal hyperactivity in multiple brain areas in the auditory pathway, including the inferior colliculus. This neuronal hyperactivity could be attributed to an imbalance between excitatory and inhibitory neurotransmission. However, it is not clear how the levels of neurotransmitters, especially neurotransmitters in the extracellular space, change over time following acoustic trauma and the development of tinnitus. In the present study, a range of amino acids were measured in the inferior colliculus of rats during acoustic trauma as well as at 1 week and 5 months post-trauma using in vivo microdialysis and high-performance liquid chromatography. Amino acid levels in response to sound stimulation were also measured at 1 week and 5 months post-trauma. It was found that unilateral exposure to a 16 kHz pure tone at 115 dB SPL for 1 h caused immediate hearing loss in all the animals and chronic tinnitus in 58 % of the animals. Comparing to the sham condition, extracellular levels of GABA were significantly increased at both the acute and 1 week time points after acoustic trauma. However, there was no significant difference in any of the amino acid levels measured between sham, tinnitus positive and tinnitus negative animals at 5 months post-trauma. There was also no clear pattern in the relationship between neurochemical changes and sound frequency/acoustic trauma/tinnitus status, which might be due to the relatively poorer temporal resolution of the microdialysis compared to electrophysiological responses.
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Affiliation(s)
- Huey Tieng Tan
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand; Brain Health Research Centre, University of Otago, Dunedin, New Zealand; Eisdell Moore Centre for Research on Hearing and Balance Disorders, University of Auckland, New Zealand
| | - Paul F Smith
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand; Brain Health Research Centre, University of Otago, Dunedin, New Zealand; Eisdell Moore Centre for Research on Hearing and Balance Disorders, University of Auckland, New Zealand
| | - Yiwen Zheng
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand; Brain Health Research Centre, University of Otago, Dunedin, New Zealand; Eisdell Moore Centre for Research on Hearing and Balance Disorders, University of Auckland, New Zealand.
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2
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Can GABAkines Quiet the Noise? The GABAA Receptor Neurobiology and Pharmacology of Tinnitus. Biochem Pharmacol 2022; 201:115067. [DOI: 10.1016/j.bcp.2022.115067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 04/21/2022] [Accepted: 04/25/2022] [Indexed: 11/20/2022]
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3
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The role of the medial geniculate body of the thalamus in the pathophysiology of tinnitus and implications for treatment. Brain Res 2022; 1779:147797. [DOI: 10.1016/j.brainres.2022.147797] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Revised: 11/25/2021] [Accepted: 01/13/2022] [Indexed: 01/12/2023]
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4
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Godfrey DA, Farms WB, Polensek S, Dunn JD, Godfrey TG. Effects of brainstem lesions on amino acid levels in the rat cochlear nucleus. Hear Res 2021; 403:108187. [PMID: 33578260 DOI: 10.1016/j.heares.2021.108187] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 01/14/2021] [Accepted: 01/20/2021] [Indexed: 11/27/2022]
Abstract
There is evidence for glutamate, γ-amino butyric acid (GABA), and glycine as neurotransmitters of centrifugal pathways to the cochlear nucleus, but the quantitative extent of their contributions to amino acid neurotransmission in cochlear nucleus regions has not been known. We used microdissection of freeze-dried tissue sections of rat cochlear nucleus, with mapping of sample locations, combined with a high performance liquid chromatography (HPLC) assay, to measure amino acid levels in cochlear nucleus subregions of rats with unilateral lesions of centrifugal pathways to the cochlear nucleus. In rats with lesions transecting all or almost all pathways to the cochlear nucleus from brain stem regions, GABA, aspartate, and glutamate levels were reduced, compared to contralateral values, in almost all ipsilateral cochlear nucleus regions. The largest reductions, in dorsal (DCN), anteroventral (AVCN), and posteroventral (PVCN) cochlear nucleus regions, approached 50% for GABA, 40% for aspartate, and 30% for glutamate. In contrast, glutamine and taurine levels were typically higher in lesioned-side cochlear nucleus regions than contralaterally. Effects on glycine levels were mixed but usually included increased lesioned-side values compared to contralateral, probably reflecting a balance between increases during protein breakdown and decreases of free glycine in transected pathways. More limited lesions transecting just dorsal pathways showed much less effect on amino acid levels. Lesion of the ipsilateral trapezoid body connection plus ipsilateral superior olivary nuclei resulted in decreases of GABA, aspartate, and glutamate levels especially in ventral cochlear nucleus regions. No clear contralateral effects of this lesion could be shown. The results most strongly support centrifugal GABAergic pathways to the cochlear nucleus, providing almost half of GABAergic neurotransmission in most regions. Our results support and extend previously published measurements of lesion effects on GABA uptake and release in cochlear nucleus subdivisions.
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Affiliation(s)
- Donald A Godfrey
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine and Life Sciences, 3000 Arlington Avenue, Toledo, OH 43614, United States.
| | - William B Farms
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine and Life Sciences, 3000 Arlington Avenue, Toledo, OH 43614, United States
| | - Sharon Polensek
- Chief of Geriatrics, Extended Care and Rehabilitation, Atlanta VA Healthcare System, and Assistant Professor of Neurology, Emory University, Atlanta, GA (Formerly Sharon Shannon-Hartman)
| | - Jon D Dunn
- Department of Anatomy, Oral Roberts University, Tulsa, OK, United States
| | - Timothy G Godfrey
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine and Life Sciences, 3000 Arlington Avenue, Toledo, OH 43614, United States
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5
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Metabolic changes in the brain and blood of rats following acoustic trauma, tinnitus and hyperacusis. PROGRESS IN BRAIN RESEARCH 2021; 262:399-430. [PMID: 33931189 DOI: 10.1016/bs.pbr.2020.09.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
It has been increasingly recognized that tinnitus is likely to be generated by complex network changes. Acoustic trauma that causes tinnitus induces significant changes in multiple metabolic pathways in the brain. However, it is not clear whether those metabolic changes in the brain could also be reflected in blood samples and whether metabolic changes could discriminate acoustic trauma, hyperacusis and tinnitus. We analyzed brain and serum metabolic changes in rats following acoustic trauma or a sham procedure using metabolomics. Hearing levels were recorded before and after acoustic trauma and behavioral measures to quantify tinnitus and hyperacusis were conducted at 4 weeks following acoustic trauma. Tissues from 11 different brain regions and serum samples were collected at about 3 months following acoustic trauma. Among the acoustic trauma animals, eight exhibited hyperacusis-like behavior and three exhibited tinnitus-like behavior. Using Gas chromatography-mass spectrometry and multivariate statistical analysis, significant metabolic changes were found in acoustic trauma animals in both the brain and serum samples with a number of metabolic pathways significantly perturbated. Furthermore, metabolic changes in the serum were able to differentiate sham from acoustic trauma animals, as well as sham from hyperacusis animals, with high accuracy. Our results suggest that serum metabolic profiling in combination with machine learning analysis may be a promising approach for identifying biomarkers for acoustic trauma, hyperacusis and potentially, tinnitus.
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6
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Zheng Y, McTavish J, Smith PF. Pharmacological Evaluation of Drugs in Animal Models of Tinnitus. Curr Top Behav Neurosci 2020; 51:51-82. [PMID: 33590458 DOI: 10.1007/7854_2020_212] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Despite the pressing need for effective drug treatments for tinnitus, currently, there is no single drug that is approved by the FDA for this purpose. Instead, a wide range of unproven over-the-counter tinnitus remedies are available on the market with little or no benefit for tinnitus but with potential harm and adverse effects. Animal models of tinnitus have played a critical role in exploring the pathophysiology of tinnitus, identifying therapeutic targets and evaluating novel and existing drugs for tinnitus treatment. This review summarises and compares the studies on pharmacological evaluation of tinnitus treatment in different animal models based on the pharmacological properties of the drug and provides insights into future directions for tinnitus drug discovery.
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Affiliation(s)
- Yiwen Zheng
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand. .,Brain Research New Zealand, Auckland, New Zealand. .,Brain Health Research Centre, University of Otago, Dunedin, New Zealand. .,Eisdell Moore Centre for Hearing and Balance Research, University of Auckland, Auckland, New Zealand.
| | - Jessica McTavish
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand.,Brain Research New Zealand, Auckland, New Zealand.,Brain Health Research Centre, University of Otago, Dunedin, New Zealand.,Eisdell Moore Centre for Hearing and Balance Research, University of Auckland, Auckland, New Zealand
| | - Paul F Smith
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand.,Brain Research New Zealand, Auckland, New Zealand.,Brain Health Research Centre, University of Otago, Dunedin, New Zealand.,Eisdell Moore Centre for Hearing and Balance Research, University of Auckland, Auckland, New Zealand
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7
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Godfrey DA, Mikesell NL, Godfrey TG, Kaltenbach JA. Amino acid and acetylcholine chemistry in mountain beaver cochlear nucleus and comparisons to pocket gopher, other rodents, and cat. Hear Res 2019; 385:107841. [PMID: 31765816 DOI: 10.1016/j.heares.2019.107841] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 10/16/2019] [Accepted: 11/06/2019] [Indexed: 11/17/2022]
Abstract
The mountain beaver and pocket gopher are two rodents that live mostly underground in tunnel systems. Previous studies have suggested that their cochlear nucleus structure, particularly that of the dorsal cochlear nucleus (DCN), differs significantly from that of other mammals, that the hearing ability of the pocket gopher is deficient compared to that of other rodents, and that the DCN of the mountain beaver is more responsive to slow oscillations of air pressure than to sounds. We conducted some electrophysiological recordings from mountain beaver DCN and then used microchemical methods to map in mountain beaver cochlear nuclei the distributions of amino acids, including the major neurotransmitters of the brain, and enzyme activities related to the metabolism of the neurotransmitter acetylcholine, which functions in centrifugal pathways to the cochlear nucleus. Similar measurements were made for a pocket gopher cochlear nucleus. Responses to tonal stimuli were found in mountain beaver DCN. Distributions and magnitudes of neurotransmitter and related amino acids within mountain beaver and pocket gopher cochlear nuclei were not very different from those of other rodents and cat. However, the enzyme of synthesis for acetylcholine, choline acetyltransferase, had only low activities in the DCN of both mountain beaver and pocket gopher. The chemical distributions in the mountain beaver DCN support a conclusion that it corresponds to just the superficial DCN portion of other mammals. High correlations between the concentrations of γ-aminobutyrate (GABA) and glycine were found for both mountain beaver and pocket gopher cochlear nuclei, suggesting that their co-localization in cochlear nucleus synapses may be especially prominent in these animals. Previous evidence suggests convergence of somatosensory and auditory information in the DCN, and this may be especially true in animals spending most of their time underground. Our results suggest that the enlarged DCN of the mountain beaver and that of the pocket gopher are not very different from those of other rodents with respect to involvement of amino acid neurotransmitters, but they appear to have reduced cholinergic innervation.
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Affiliation(s)
- Donald A Godfrey
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine and Life Sciences, Toledo, OH, USA.
| | - Nikki L Mikesell
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine and Life Sciences, Toledo, OH, USA
| | - Timothy G Godfrey
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine and Life Sciences, Toledo, OH, USA
| | - James A Kaltenbach
- Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA
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8
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Exploring pathogenesis in subjects with subjective Tinnitus having kidney deficiency pattern in terms of Traditional Chinese Medicine based on serum metabolic profiles. J TRADIT CHIN MED 2018. [DOI: 10.1016/s0254-6272(18)30918-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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9
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Cacace AT, Hu J, Romero S, Xuan Y, Burkard RF, Tyler RS. Glutamate is down-regulated and tinnitus loudness-levels decreased following rTMS over auditory cortex of the left hemisphere: A prospective randomized single-blinded sham-controlled cross-over study. Hear Res 2018; 358:59-73. [DOI: 10.1016/j.heares.2017.10.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 10/25/2017] [Accepted: 10/31/2017] [Indexed: 12/14/2022]
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10
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Godfrey DA, Chen K, O'Toole TR, Mustapha AI. Amino acid and acetylcholine chemistry in the central auditory system of young, middle-aged and old rats. Hear Res 2017; 350:173-188. [DOI: 10.1016/j.heares.2017.05.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 04/24/2017] [Accepted: 05/03/2017] [Indexed: 02/04/2023]
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Riga M, Komis A, Marangoudakis P, Naxakis S, Ferekidis E, Kandiloros D, Danielides V. Differences in the suppression of distortion product otoacoustic emissions by contralateral white noise between patients with acute or chronic tinnitus. Int J Audiol 2017; 56:589-595. [DOI: 10.1080/14992027.2017.1305516] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Maria Riga
- University Hospital of Alexandroupolis, Democritus University of Thrace, Alexandroupolis, Greece,
| | - Agis Komis
- Attikon University Hospital, National University of Athens, Athens, Greece,
| | | | - Stefanos Naxakis
- University Hospital of Patras, University of Patras, Patras, Greece, and
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12
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He J, Zhu Y, Aa J, Smith PF, De Ridder D, Wang G, Zheng Y. Brain Metabolic Changes in Rats following Acoustic Trauma. Front Neurosci 2017; 11:148. [PMID: 28392756 PMCID: PMC5364180 DOI: 10.3389/fnins.2017.00148] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 03/09/2017] [Indexed: 12/14/2022] Open
Abstract
Acoustic trauma is the most common cause of hearing loss and tinnitus in humans. However, the impact of acoustic trauma on system biology is not fully understood. It has been increasingly recognized that tinnitus caused by acoustic trauma is unlikely to be generated by a single pathological source, but rather a complex network of changes involving not only the auditory system but also systems related to memory, emotion and stress. One obvious and significant gap in tinnitus research is a lack of biomarkers that reflect the consequences of this interactive "tinnitus-causing" network. In this study, we made the first attempt to analyse brain metabolic changes in rats following acoustic trauma using metabolomics, as a pilot study prior to directly linking metabolic changes to tinnitus. Metabolites in 12 different brain regions collected from either sham or acoustic trauma animals were profiled using a gas chromatography mass spectrometry (GC/MS)-based metabolomics platform. After deconvolution of mass spectra and identification of the molecules, the metabolomic data were processed using multivariate statistical analysis. Principal component analysis showed that metabolic patterns varied among different brain regions; however, brain regions with similar functions had a similar metabolite composition. Acoustic trauma did not change the metabolite clusters in these regions. When analyzed within each brain region using the orthogonal projection to latent structures discriminant analysis sub-model, 17 molecules showed distinct separation between control and acoustic trauma groups in the auditory cortex, inferior colliculus, superior colliculus, vestibular nucleus complex (VNC), and cerebellum. Further metabolic pathway impact analysis and the enrichment overview with network analysis suggested the primary involvement of amino acid metabolism, including the alanine, aspartate and glutamate metabolic pathways, the arginine and proline metabolic pathways and the purine metabolic pathway. Our results provide the first metabolomics evidence that acoustic trauma can induce changes in multiple metabolic pathways. This pilot study also suggests that the metabolomic approach has the potential to identify acoustic trauma-specific metabolic shifts in future studies where metabolic changes are correlated with the animal's tinnitus status.
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Affiliation(s)
- Jun He
- Key Laboratory of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University Nanjing, Jiangsu, China
| | - Yejin Zhu
- Key Laboratory of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University Nanjing, Jiangsu, China
| | - Jiye Aa
- Key Laboratory of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University Nanjing, Jiangsu, China
| | - Paul F Smith
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of OtagoDunedin, New Zealand; Brain Health Research Centre, University of OtagoDunedin, New Zealand; Brain Research New ZealandDunedin, New Zealand; Eisdell Moore Centre for Hearing and Balance Research, University of AucklandAuckland, New Zealand
| | - Dirk De Ridder
- Brain Health Research Centre, University of OtagoDunedin, New Zealand; Brain Research New ZealandDunedin, New Zealand; Eisdell Moore Centre for Hearing and Balance Research, University of AucklandAuckland, New Zealand; Department of Neurosurgery, Dunedin Medical School, University of OtagoOtago, New Zealand
| | - Guangji Wang
- Key Laboratory of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University Nanjing, Jiangsu, China
| | - Yiwen Zheng
- Department of Pharmacology and Toxicology, School of Biomedical Sciences, University of OtagoDunedin, New Zealand; Brain Health Research Centre, University of OtagoDunedin, New Zealand; Brain Research New ZealandDunedin, New Zealand; Eisdell Moore Centre for Hearing and Balance Research, University of AucklandAuckland, New Zealand
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13
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Godfrey DA, Lee AC, Hamilton WD, Benjamin LC, Vishwanath S, Simo H, Godfrey LM, Mustapha AIAA, Heffner RS. Volumes of cochlear nucleus regions in rodents. Hear Res 2016; 339:161-174. [PMID: 27435005 DOI: 10.1097/sla.0000000000001177.complications] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 07/15/2016] [Indexed: 05/25/2023]
Abstract
The cochlear nucleus receives all the coded information about sound from the cochlea and is the source of auditory information for the rest of the central auditory system. As such, it is a critical auditory nucleus. The sizes of the cochlear nucleus as a whole and its three major subdivisions - anteroventral cochlear nucleus (AVCN), posteroventral cochlear nucleus (PVCN), and dorsal cochlear nucleus (DCN) - have been measured in a large number of mammals, but measurements of its subregions at a more detailed level for a variety of species have not previously been made. Size measurements are reported here for the summed granular regions, DCN layers, AVCN, PVCN, and interstitial nucleus in 15 different rodent species, as well as a lagomorph, carnivore, and small primate. This further refinement of measurements is important because the granular regions and superficial layers of the DCN appear to have some different functions than the other cochlear nucleus regions. Except for DCN layers in the mountain beaver, all regions were clearly identifiable in all the animals studied. Relative regional size differences among most of the rodents, and even the 3 non-rodents, were not large and did not show a consistent relation to their wide range of lifestyles and hearing parameters. However, the mountain beaver, and to a lesser extent the pocket gopher, two rodents that live in tunnel systems, had relative sizes of summed granular regions and DCN molecular layer distinctly larger than those of the other mammals. Among all the mammals studied, there was a high correlation between the size per body weight of summed granular regions and that of the DCN molecular layer, consistent with other evidence for a close relationship between granule cells and superficial DCN neurons.
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Affiliation(s)
- Donald A Godfrey
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States.
| | - Augustine C Lee
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Walter D Hamilton
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Louis C Benjamin
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Shilpa Vishwanath
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Hermann Simo
- Department of Medicine, University of Toledo, United States
| | - Lynn M Godfrey
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Abdurrahman I A A Mustapha
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
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14
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Godfrey DA, Lee AC, Hamilton WD, Benjamin LC, Vishwanath S, Simo H, Godfrey LM, Mustapha AIAA, Heffner RS. Volumes of cochlear nucleus regions in rodents. Hear Res 2016; 339:161-74. [PMID: 27435005 PMCID: PMC5835392 DOI: 10.1016/j.heares.2016.07.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 07/15/2016] [Indexed: 01/31/2023]
Abstract
The cochlear nucleus receives all the coded information about sound from the cochlea and is the source of auditory information for the rest of the central auditory system. As such, it is a critical auditory nucleus. The sizes of the cochlear nucleus as a whole and its three major subdivisions - anteroventral cochlear nucleus (AVCN), posteroventral cochlear nucleus (PVCN), and dorsal cochlear nucleus (DCN) - have been measured in a large number of mammals, but measurements of its subregions at a more detailed level for a variety of species have not previously been made. Size measurements are reported here for the summed granular regions, DCN layers, AVCN, PVCN, and interstitial nucleus in 15 different rodent species, as well as a lagomorph, carnivore, and small primate. This further refinement of measurements is important because the granular regions and superficial layers of the DCN appear to have some different functions than the other cochlear nucleus regions. Except for DCN layers in the mountain beaver, all regions were clearly identifiable in all the animals studied. Relative regional size differences among most of the rodents, and even the 3 non-rodents, were not large and did not show a consistent relation to their wide range of lifestyles and hearing parameters. However, the mountain beaver, and to a lesser extent the pocket gopher, two rodents that live in tunnel systems, had relative sizes of summed granular regions and DCN molecular layer distinctly larger than those of the other mammals. Among all the mammals studied, there was a high correlation between the size per body weight of summed granular regions and that of the DCN molecular layer, consistent with other evidence for a close relationship between granule cells and superficial DCN neurons.
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Affiliation(s)
- Donald A Godfrey
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States.
| | - Augustine C Lee
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Walter D Hamilton
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Louis C Benjamin
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Shilpa Vishwanath
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Hermann Simo
- Department of Medicine, University of Toledo, United States
| | - Lynn M Godfrey
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
| | - Abdurrahman I A A Mustapha
- Department of Neurology, University of Toledo, United States; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo, United States
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15
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Knipper M, Panford-Walsh R, Singer W, Rüttiger L, Zimmermann U. Specific synaptopathies diversify brain responses and hearing disorders: you lose the gain from early life. Cell Tissue Res 2015; 361:77-93. [PMID: 25843689 PMCID: PMC4487345 DOI: 10.1007/s00441-015-2168-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 03/05/2015] [Indexed: 01/08/2023]
Abstract
Before hearing onset, inner hair cell (IHC) maturation proceeds under the influence of spontaneous Ca(2+) action potentials (APs). The temporal signature of the IHC Ca(2+) AP is modified through an efferent cholinergic feedback from the medial olivocochlear bundle (MOC) and drives the IHC pre- and post-synapse phenotype towards low spontaneous (spike) rate (SR), high-threshold characteristics. With sensory experience, the IHC pre- and post-synapse phenotype matures towards the instruction of low-SR, high-threshold and of high-SR, low-threshold auditory fiber characteristics. Corticosteroid feedback together with local brain-derived nerve growth factor (BDNF) and catecholaminergic neurotransmitters (dopamine) might be essential for this developmental step. In this review, we address the question of whether the control of low-SR and high-SR fiber characteristics is linked to various degrees of vulnerability of auditory fibers in the mature system. In particular, we examine several IHC synaptopathies in the context of various hearing disorders and exemplified shortfalls before and after hearing onset.
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Affiliation(s)
- Marlies Knipper
- Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Center (THRC), Molecular Physiology of Hearing, University of Tübingen, Elfriede-Aulhorn-Straße 5, 72076 Tübingen, Germany
| | | | - Wibke Singer
- Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Center (THRC), Molecular Physiology of Hearing, University of Tübingen, Elfriede-Aulhorn-Straße 5, 72076 Tübingen, Germany
| | - Lukas Rüttiger
- Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Center (THRC), Molecular Physiology of Hearing, University of Tübingen, Elfriede-Aulhorn-Straße 5, 72076 Tübingen, Germany
| | - Ulrike Zimmermann
- Department of Otolaryngology, Head and Neck Surgery, Tübingen Hearing Research Center (THRC), Molecular Physiology of Hearing, University of Tübingen, Elfriede-Aulhorn-Straße 5, 72076 Tübingen, Germany
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Godfrey DA, Chen K, Godfrey MA, Lee AC, Crass SP, Shipp D, Simo H, Robinson KT. Cochlear ablation effects on amino acid levels in the chinchilla cochlear nucleus. Neuroscience 2015; 297:137-59. [PMID: 25839146 DOI: 10.1016/j.neuroscience.2015.03.055] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Revised: 03/06/2015] [Accepted: 03/24/2015] [Indexed: 10/23/2022]
Abstract
Inner ear damage can lead to hearing disorders, including tinnitus, hyperacusis, and hearing loss. We measured the effects of severe inner ear damage, produced by cochlear ablation, on the levels and distributions of amino acids in the first brain center of the auditory system, the cochlear nucleus. Measurements were also made for its projection pathways and the superior olivary nuclei. Cochlear ablation produces complete degeneration of the auditory nerve, which provides a baseline for interpreting the effects of partial damage to the inner ear, such as that from ototoxic drugs or intense sound. Amino acids play a critical role in neural function, including neurotransmission, neuromodulation, cellular metabolism, and protein construction. They include major neurotransmitters of the brain - glutamate, glycine, and γ-aminobutyrate (GABA) - as well as others closely related to their metabolism and/or functions - aspartate, glutamine, and taurine. Since the effects of inner ear damage develop over time, we measured the changes in amino acid levels at various survival times after cochlear ablation. Glutamate and aspartate levels decreased by 2weeks in the ipsilateral ventral cochlear nucleus and deep layer of the dorsal cochlear nucleus, with the largest decreases in the posteroventral cochlear nucleus (PVCN): 66% for glutamate and 63% for aspartate. Aspartate levels also decreased in the lateral part of the ipsilateral trapezoid body, by as much as 50%, suggesting a transneuronal effect. GABA and glycine levels showed some bilateral decreases, especially in the PVCN. These results may represent the state of amino acid metabolism in the cochlear nucleus of humans after removal of eighth nerve tumors, which may adversely result in destruction of the auditory nerve. Measurement of chemical changes following inner ear damage may increase understanding of the pathogenesis of hearing impairments and enable improvements in their diagnosis and treatment.
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Affiliation(s)
- D A Godfrey
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA.
| | - K Chen
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - M A Godfrey
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - A C Lee
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - S P Crass
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - D Shipp
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - H Simo
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA
| | - K T Robinson
- Department of Neurology, University of Toledo College of Medicine, Mail Stop 1195, 3000 Arlington Avenue, Toledo, OH 43614, USA; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, 3000 Arlington Avenue, Toledo, OH 43614, USA
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Berger JI, Coomber B. Tinnitus-related changes in the inferior colliculus. Front Neurol 2015; 6:61. [PMID: 25870582 PMCID: PMC4378364 DOI: 10.3389/fneur.2015.00061] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 03/09/2015] [Indexed: 12/21/2022] Open
Abstract
Tinnitus is highly complex, diverse, and difficult to treat, in part due to the fact that the underlying causes and mechanisms remain elusive. Tinnitus is generated within the auditory brain; however, consolidating our understanding of tinnitus pathophysiology is difficult due to the diversity of reported effects and the variety of implicated brain nuclei. Here, we focus on the inferior colliculus (IC), a midbrain structure that integrates the vast majority of ascending auditory information and projects via the thalamus to the auditory cortex. The IC is also a point of convergence for corticofugal input and input originating outside the auditory pathway. We review the evidence, from both studies with human subjects and from animal models, for the contribution the IC makes to tinnitus. Changes in the IC, caused by either noise exposure or drug administration, involve fundamental, heterogeneous alterations in the balance of excitation and inhibition. However, differences between hearing loss-induced pathology and tinnitus-related pathology are not well understood. Moreover, variability in tinnitus induction methodology has a significant impact on subsequent neural and behavioral changes, which could explain some of the seemingly contradictory data. Nonetheless, the IC is likely involved in the generation and persistence of tinnitus perception.
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Affiliation(s)
- Joel I Berger
- Medical Research Council Institute of Hearing Research, University of Nottingham , Nottingham , UK
| | - Ben Coomber
- Medical Research Council Institute of Hearing Research, University of Nottingham , Nottingham , UK
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Lee AC, Godfrey DA. Cochlear damage affects neurotransmitter chemistry in the central auditory system. Front Neurol 2014; 5:227. [PMID: 25477858 PMCID: PMC4237057 DOI: 10.3389/fneur.2014.00227] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Accepted: 10/20/2014] [Indexed: 02/04/2023] Open
Abstract
Tinnitus, the perception of a monotonous sound not actually present in the environment, affects nearly 20% of the population of the United States. Although there has been great progress in tinnitus research over the past 25 years, the neurochemical basis of tinnitus is still poorly understood. We review current research about the effects of various types of cochlear damage on the neurotransmitter chemistry in the central auditory system and document evidence that different changes in this chemistry can underlie similar behaviorally measured tinnitus symptoms. Most available data have been obtained from rodents following cochlear damage produced by cochlear ablation, intense sound, or ototoxic drugs. Effects on neurotransmitter systems have been measured as changes in neurotransmitter level, synthesis, release, uptake, and receptors. In this review, magnitudes of changes are presented for neurotransmitter-related amino acids, acetylcholine, and serotonin. A variety of effects have been found in these studies that may be related to animal model, survival time, type and/or magnitude of cochlear damage, or methodology. The overall impression from the evidence presented is that any imbalance of neurotransmitter-related chemistry could disrupt auditory processing in such a way as to produce tinnitus.
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Affiliation(s)
- Augustine C Lee
- Department of Neurology, University of Toledo College of Medicine , Toledo, OH , USA ; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine , Toledo, OH , USA
| | - Donald A Godfrey
- Department of Neurology, University of Toledo College of Medicine , Toledo, OH , USA ; Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine , Toledo, OH , USA
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Gourévitch B, Edeline JM, Occelli F, Eggermont JJ. Is the din really harmless? Long-term effects of non-traumatic noise on the adult auditory system. Nat Rev Neurosci 2014; 15:483-91. [DOI: 10.1038/nrn3744] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Godfrey DA, Jin YM, Liu X, Godfrey MA. Effects of cochlear ablation on amino acid levels in the rat cochlear nucleus and superior olive. Hear Res 2014; 309:44-54. [PMID: 24291808 PMCID: PMC5819880 DOI: 10.1016/j.heares.2013.11.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 11/05/2013] [Accepted: 11/19/2013] [Indexed: 11/21/2022]
Abstract
Amino acids have important roles in the chemistry of the auditory system, including communication among neurons. There is much evidence for glutamate as a neurotransmitter from auditory nerve fibers to cochlear nucleus neurons. Previous studies in rodents have examined effects of removal of auditory nerve input by cochlear ablation on levels, uptake and release of glutamate in cochlear nucleus subdivisions, as well as on glutamate receptors. Effects have also been reported on uptake and release of γ-aminobutyrate (GABA) and glycine, two other amino acids strongly implicated in cochlear nucleus synaptic transmission. We mapped the effects of cochlear ablation on the levels of amino acids, including glutamate, GABA, glycine, aspartate, glutamine, taurine, serine, threonine, and arginine, in microscopic subregions of the rat cochlear nucleus. Submicrogram-size samples microdissected from freeze-dried brainstem sections were assayed for amino acid levels by high performance liquid chromatography. After cochlear ablation, glutamate and aspartate levels decreased by 2 days in regions receiving relatively dense innervation from the auditory nerve, whereas the levels of most other amino acids increased. The results are consistent with a close association of glutamate and aspartate with auditory nerve fibers and of other amino acids with other neurons and glia in the cochlear nucleus. A consistent decrease of GABA level in the lateral superior olive could be consistent with a role in some lateral olivocochlear neurons. The results are compared with those obtained with the same methods for the rat vestibular nerve root and nuclei after vestibular ganglionectomy.
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Affiliation(s)
- Donald A Godfrey
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, Toledo, OH, USA.
| | - Yong-Ming Jin
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, Toledo, OH, USA
| | - Xiaochen Liu
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, Toledo, OH, USA
| | - Matthew A Godfrey
- Department of Neurology and Division of Otolaryngology and Dentistry, Department of Surgery, University of Toledo College of Medicine, Toledo, OH, USA
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Knipper M, Van Dijk P, Nunes I, Rüttiger L, Zimmermann U. Advances in the neurobiology of hearing disorders: Recent developments regarding the basis of tinnitus and hyperacusis. Prog Neurobiol 2013; 111:17-33. [DOI: 10.1016/j.pneurobio.2013.08.002] [Citation(s) in RCA: 155] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Revised: 08/20/2013] [Accepted: 08/20/2013] [Indexed: 10/26/2022]
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Benson RR, Gattu R, Cacace AT. Left hemisphere fractional anisotropy increase in noise-induced tinnitus: a diffusion tensor imaging (DTI) study of white matter tracts in the brain. Hear Res 2013; 309:8-16. [PMID: 24212050 DOI: 10.1016/j.heares.2013.10.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 10/17/2013] [Accepted: 10/22/2013] [Indexed: 11/17/2022]
Abstract
Diffusion tensor imaging (DTI) is a contemporary neuroimaging modality used to study connectivity patterns and microstructure of white matter tracts in the brain. The use of DTI in the study of tinnitus is a relatively unexplored methodology with no studies focusing specifically on tinnitus induced by noise exposure. In this investigation, participants were two groups of adults matched for etiology, age, and degree of peripheral hearing loss, but differed by the presence or absence (+/-) of tinnitus. It is assumed that matching individuals on the basis of peripheral hearing loss, allows for differentiating changes in white matter microstructure due to hearing loss from changes due to the effects of chronic tinnitus. Alterations in white matter tracts, using the fractional anisotropy (FA) metric, which measures directional diffusion of water, were quantified using tract-based spatial statistics (TBSS) with additional details provided by in vivo probabilistic tractography. Our results indicate that 10 voxel clusters differentiated the two groups, including 9 with higher FA in the group with tinnitus. A decrease in FA was found for a single cluster in the group with tinnitus. However, seven of the 9 clusters with higher FA were in left hemisphere thalamic, frontal, and parietal white matter. These foci were localized to the anterior thalamic radiations and the inferior and superior longitudinal fasciculi. The two right-sided clusters with increased FA were located in the inferior fronto-occipital fasciculus and superior longitudinal fasciculus. The only decrease in FA for the tinnitus-positive group was found in the superior longitudinal fasciculus of the left parietal lobe.
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Affiliation(s)
| | - Ramtilak Gattu
- Department of Radiology, Wayne State University School of Medicine, Detroit, MI, USA
| | - Anthony T Cacace
- Department of Communication Sciences & Disorders, Wayne State University, 207 Rackham, 60 Farnsworth, Detroit, MI 48202, USA.
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Cai R, Kalappa BI, Brozoski TJ, Ling LL, Caspary DM. Is GABA neurotransmission enhanced in auditory thalamus relative to inferior colliculus? J Neurophysiol 2013; 111:229-38. [PMID: 24155003 DOI: 10.1152/jn.00556.2013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central auditory system. Sensory thalamic structures show high levels of non-desensitizing extrasynaptic GABAA receptors (GABAARs) and a reduction in the redundancy of coded information. The present study compared the inhibitory potency of GABA acting at GABAARs between the inferior colliculus (IC) and the medial geniculate body (MGB) using quantitative in vivo, in vitro, and ex vivo experimental approaches. In vivo single unit studies compared the ability of half maximal inhibitory concentrations of GABA to inhibit sound-evoked temporal responses, and found that GABA was two to three times (P < 0.01) more potent at suppressing MGB single unit responses than IC unit responses. In vitro whole cell patch-clamp slice recordings were used to demonstrate that gaboxadol, a δ-subunit selective GABAAR agonist, was significantly more potent at evoking tonic inhibitory currents from MGB neurons than IC neurons (P < 0.01). These electrophysiological findings were supported by an in vitro receptor binding assay which used the picrotoxin analog [(3)H]TBOB to assess binding in the GABAAR chloride channel. MGB GABAARs had significantly greater total open chloride channel capacity relative to GABAARs in IC (P < 0.05) as shown by increased total [(3)H]TBOB binding. Finally, a comparative ex vivo measurement compared endogenous GABA levels and suggested a trend towards higher GABA concentrations in MGB than in IC. Collectively, these studies suggest that, per unit GABA, high affinity extrasynaptic and synaptic GABAARs confer a significant inhibitory GABAAR advantage to MGB neurons relative to IC neurons. This increased GABA sensitivity likely underpins the vital filtering role of auditory thalamus.
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Affiliation(s)
- Rui Cai
- Southern Illinois University School of Medicine, Department of Pharmacology, Springfield, Illinois; and
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Godfrey DA, Kaltenbach JA, Chen K, Ilyas O. Choline acetyltransferase activity in the hamster central auditory system and long-term effects of intense tone exposure. J Neurosci Res 2013; 91:987-96. [PMID: 23605746 PMCID: PMC4469331 DOI: 10.1002/jnr.23227] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Revised: 02/18/2013] [Accepted: 02/27/2013] [Indexed: 12/19/2022]
Abstract
Acoustic trauma often leads to loss of hearing of environmental sounds, tinnitus, in which a monotonous sound not actually present is heard, and/or hyperacusis, in which there is an abnormal sensitivity to sound. Research on hamsters has documented physiological effects of exposure to intense tones, including increased spontaneous neural activity in the dorsal cochlear nucleus. Such physiological changes should be accompanied by chemical changes, and those chemical changes associated with chronic effects should be present at long times after the intense sound exposure. Using a microdissection mapping procedure combined with a radiometric microassay, we have measured activities of choline acetyltransferase (ChAT), the enzyme responsible for synthesis of the neurotransmitter acetylcholine, in the cochlear nucleus, superior olive, inferior colliculus, and auditory cortex of hamsters 5 months after exposure to an intense tone compared with control hamsters of the same age. In control hamsters, ChAT activities in auditory regions were never more than one-tenth of the ChAT activity in the facial nerve root, a bundle of myelinated cholinergic axons, in agreement with a modulatory rather than a dominant role of acetylcholine in hearing. Within auditory regions, relatively higher activities were found in granular regions of the cochlear nucleus, dorsal parts of the superior olive, and auditory cortex. In intense-tone-exposed hamsters, ChAT activities were significantly increased in the anteroventral cochlear nucleus granular region and the lateral superior olivary nucleus. This is consistent with some chronic upregulation of the cholinergic olivocochlear system influence on the cochlear nucleus after acoustic trauma.
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Affiliation(s)
- Donald A Godfrey
- Department of Neurology, University of Toledo College of Medicine, Toledo, Ohio 43614, USA.
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