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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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Fan GR, Yin ZD, Sun Y, Chen S, Zhang WJ, Huang X, Kong WJ, Zhang HL. Reversible neurotoxicity of kanamycin on dorsal cochlear nucleus. Brain Res 2013; 1502:30-46. [PMID: 23333799 DOI: 10.1016/j.brainres.2012.12.049] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Revised: 10/13/2012] [Accepted: 12/27/2012] [Indexed: 01/05/2023]
Abstract
The time course of aminoglycoside neurotoxic effect on cochlear nucleus is still obscure. We examined dynamic pathological changes of dorsal cochlear nucleus (DCN) and investigated whether apoptosis or autophagy was upregulated in the neurotoxic course of kanamycin on DCN after kanamycin treatment. Rats were treated with kanamycin sulfate/kg/day at a dose of 500mg by subcutaneous injection for 10 days. Dynamic pathological changes, neuron density and neuron apoptosis of the DCN were examined at 1, 7, 14, 28, 56, 70 and 140 days after kanamycin treatment. The expressions of JNK1, DAPK2, Bcl-2, p-Bcl-2, Caspase-3, LC3B and Beclin-1 were also detected. Under transmission electron microscopy, the mitochondrial swelling and focal vacuoles as well as endoplasmic reticulum dilation were progressively aggravated from 1 day to 14 days, and gradually recovered from 28 days to 140 days. Meanwhile, both autophagosomes and autolysosomes were increased from 1 day to 56 days. Only few neurons were positive to the TUNEL staining. Moreover, neither the expressions of caspase-3 and DAPK2 nor neurons density of DCN changed significantly. LC3-II was drastically increased at 7 days. Beclin-1 was upgraded at 1 and 7 days. P-Bcl-2 increased at 1, 7, 14 and 28 days. JNK1 increased at 7 days, and Bcl-2 was downgraded at 140 days. LC3-B positive neurons were increased at 1, 7 and 14 days. These data demonstrated that the neurons damage of the DCN caused by kanamycin was reversible and autophagy was upregulated in the neurotoxic course of kanamycin on DCN through JNK1-mediated phosphorylation of Bcl-2 pathway.
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Affiliation(s)
- Guo-Run Fan
- Department of Otorhinolaryngology, Union Hospital of Tongji Medical College, Huazhong University of Science and Technology, Jiefang Avenue 1277, Wuhan 430022, PR China
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Xu M, Hu HT, Jin Z, Chen G, Wang WX, Fan YL, Anniko M, Duan M. Ototoxicity on cochlear nucleus neurons following systemic application of gentamicin. Acta Otolaryngol 2009; 129:745-8. [PMID: 18855163 DOI: 10.1080/00016480802454716] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
CONCLUSION The gentamicin-induced pathological alteration in the cochlear nucleus is not exclusively a secondary consequence of the damage in the cochlea. Instead, the toxic effect of gentamicin on the cochlear nucleus may occur simultaneously or even earlier than that on the cochlea. OBJECTIVES To investigate the pathological alteration of cochlear nucleus neurons in guinea pigs following systemic application of gentamicin. MATERIALS AND METHODS Guinea pigs were injected with gentamicin for 1 day, 3 days, 1 week, 2 weeks, and 3 weeks, respectively. In gentamicin-treated animals, the hearing function was evaluated by measuring the auditory brainstem response (ABR). The number and cross-sectional area of substance P-positive neurons in the cochlear nucleus were also measured. RESULTS The threshold of ABR and the number of substance P-positive neurons in the cochlear nucleus were significantly increased after 1 week and 3 days of injection of gentamicin, respectively. The cross-sectional area of substance P-positive neurons in the cochlear nucleus was significantly reduced after 1-day injection of gentamicin.
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Stakhovskaya O, Hradek GT, Snyder RL, Leake PA. Effects of age at onset of deafness and electrical stimulation on the developing cochlear nucleus in cats. Hear Res 2008; 243:69-77. [PMID: 18590947 DOI: 10.1016/j.heares.2008.05.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2008] [Revised: 05/14/2008] [Accepted: 05/20/2008] [Indexed: 10/22/2022]
Abstract
This study examined the effects of deafness and intracochlear electrical stimulation on the anatomy of the cochlear nucleus (CN) after a brief period of normal auditory development early in life. Kittens were deafened by systemic ototoxic drug injections either as neonates or starting at postnatal day 30. Total CN volume, individual CN subdivision volumes, and cross-sectional areas of spherical cell somata in the anteroventral CN (AVCN) were compared in neonatally deafened and 30-day deafened groups at 8 weeks of age and in young adults after approximately 6 months of electrical stimulation initiated at 8 weeks of age. Both neonatal and early acquired hearing loss resulted in a reduction in CN volume as compared to normal hearing cats. Comparison of 8- and 32-week old groups indicated that the CN continued to grow in both deafened groups despite the absence of auditory input. Preserving normal auditory input for 30 days resulted in a significant increase in both total CN volume and cross-sectional areas of spherical cell somata, as compared to neonatally deafened animals. Restoring auditory input in these developing animals by unilateral intracochlear electrical stimulation did not elicit any difference in CN volume between the two sides, but resulted in 7% larger spherical cell size on the stimulated side. Overall, the brief period of normal auditory development and subsequent electrical stimulation maintained CN volume at 80% of normal and spherical cell size at 86% of normal ipsilateral to the implant as compared to 67% and 74%, respectively, in the neonatally deafened group.
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Affiliation(s)
- Olga Stakhovskaya
- Epstein Laboratory, Department of Otolaryngology, Head and Neck Surgery, University of California San Francisco, San Francisco, CA 94143-0526, USA.
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Osofsky MR, Moore CM, Leake PA. Does exogenous GM1 ganglioside enhance the effects of electrical stimulation in ameliorating degeneration after neonatal deafness? Hear Res 2001; 159:23-35. [PMID: 11520632 DOI: 10.1016/s0378-5955(01)00311-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
This study examined the combined effects of administration of exogenous GM1 ganglioside and electrical stimulation on the cochlear nucleus (CN) of cats deafened neonatally by ototoxic drugs. Five normal hearing adult cats served as controls. Another 12 cats were deafened bilaterally by daily injections of neomycin sulfate (60 mg/kg) for 17-21 days after birth until auditory brainstem testing demonstrated profound hearing loss. Six of the deaf animals comprised the GM1 group, which received daily injections of GM1 ganglioside (30 mg/kg) for 28-38 days during the period after profound deafness was confirmed, and prior to receiving a cochlear implant. The non-GM1 group (n=6) received no treatment during this interim period. All the deafened animals underwent unilateral cochlear implantation at 6-9 weeks postnatal and received several months (mean duration, 32 weeks) of chronic electrical stimulation (4 h/day, 5 days/week). Stimulation was delivered by intracochlear bipolar electrodes, using electrical signals that were designed to be temporally challenging to the central auditory system. Results showed that in the neonatally deafened animals, both the GM1 and non-GM1 groups, the volume of the CN was markedly reduced (to 76% of normal), but there was no difference between the animals that received GM1 and those that did not. The cross sectional areas of spherical cell somata in both GM1 and non-GM1 groups also showed a highly significant reduction in size, to < or =75% of normal after neonatal deafening. Moreover, in both the GM1 and non-GM1 groups, the spherical cells in the CN ipsilateral to the implanted cochlea were significantly larger (6%) than cells in the control, unstimulated CN. Again, however, there was no significant difference between the GM1 group and the non-GM1 group in spherical cell size. These results contrast sharply with previous reports that exogenous GM1 prevents CN degeneration after neonatal conductive hearing loss and partially prevents spiral ganglion cell degeneration when administered immediately after ototoxic drug deafening in adult animals. Taken together, findings to date suggest that GM1 may be effective in preventing degeneration only if the GM1 is administered immediately at the time hearing loss occurs.
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Affiliation(s)
- M R Osofsky
- Epstein Laboratories, Department of Otolaryngology, HNS, University of California San Francisco, 533 Parnassus Ave., Room U-490, San Francisco, CA 94143-0526, USA
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Abstract
HYPOTHESIS Sensorineural hearing loss may be associated with altered patterns of neuronal connections within the central auditory pathway. STUDY DESIGN The cat auditory system was used to address the relative importance of impulse traffic within the auditory nerve in maintaining central nervous system connections. METHODS Acute, unilateral deafness was induced by tetrodotoxin intoxication of cochlear hair cells. Analysis focused on the structural patterns of contact between auditory nerve endings called end bulbs of Held and their target neurons. Specifically, end bulb morphology and target cell size within the cochlear nucleus were examined. Highly specialized synaptic contacts at this junction provide a powerful site for study. RESULTS The principal finding was that abolished activity in the auditory nerve caused nerve endings to assume a different shape, typified by more branching and smaller terminal swellings. The new shape is one typically associated with only a subpopulation of fibers in normal-hearing cats--those exhibiting a high-threshold, low-spontaneous activity profile. This result implies that abolished activity alters patterns of nerve fiber contact with second-order neurons. Tetrodotoxin produced differential effects on subpopulations of target neurons within the brainstem and is interpretable on the basis of "weighing" synaptic inputs. Second-order neurons that receive large axosomatic inputs from their parent fiber were significantly smaller than neurons that receive small, axodendritic terminals. Thus, attenuated auditory activity may produce differential effects across the auditory pathway, thereby disrupting the normal balance of inputs into synaptic stations. CONCLUSIONS Impulse traffic is a critical factor in the interaction between the ear and central auditory stations and appears necessary for the maintenance of key synapses. As hearing disorders with impaired comprehension may be modeled by studies of auditory deafferentation, these observations extend the possibility that changes in central neuronal connections underlie reduced capabilities for processing restored auditory input.
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Affiliation(s)
- J K Niparko
- Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Maryland 21287-0910, USA
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