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Williams IR, Ryugo DK. Bilateral and symmetric glycinergic and glutamatergic projections from the LSO to the IC in the CBA/CaH mouse. Front Neural Circuits 2024; 18:1430598. [PMID: 39184455 PMCID: PMC11341401 DOI: 10.3389/fncir.2024.1430598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2024] [Accepted: 07/10/2024] [Indexed: 08/27/2024] Open
Abstract
Auditory space has been conceptualized as a matrix of systematically arranged combinations of binaural disparity cues that arise in the superior olivary complex (SOC). The computational code for interaural time and intensity differences utilizes excitatory and inhibitory projections that converge in the inferior colliculus (IC). The challenge is to determine the neural circuits underlying this convergence and to model how the binaural cues encode location. It has been shown that midbrain neurons are largely excited by sound from the contralateral ear and inhibited by sound leading at the ipsilateral ear. In this context, ascending projections from the lateral superior olive (LSO) to the IC have been reported to be ipsilaterally glycinergic and contralaterally glutamatergic. This study used CBA/CaH mice (3-6 months old) and applied unilateral retrograde tracing techniques into the IC in conjunction with immunocytochemical methods with glycine and glutamate transporters (GlyT2 and vGLUT2, respectively) to analyze the projection patterns from the LSO to the IC. Glycinergic and glutamatergic neurons were spatially intermixed within the LSO, and both types projected to the IC. For GlyT2 and vGLUT2 neurons, the average percentage of ipsilaterally and contralaterally projecting cells was similar (ANOVA, p = 0.48). A roughly equal number of GlyT2 and vGLUT2 neurons did not project to the IC. The somatic size and shape of these neurons match the descriptions of LSO principal cells. A minor but distinct population of small (< 40 μm2) neurons that labeled for GlyT2 did not project to the IC; these cells emerge as candidates for inhibitory local circuit neurons. Our findings indicate a symmetric and bilateral projection of glycine and glutamate neurons from the LSO to the IC. The differences between our results and those from previous studies suggest that species and habitat differences have a significant role in mechanisms of binaural processing and highlight the importance of research methods and comparative neuroscience. These data will be important for modeling how excitatory and inhibitory systems converge to create auditory space in the CBA/CaH mouse.
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Affiliation(s)
- Isabella R. Williams
- Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
- School of Medical Sciences, University of New South Wales, Kensington, NSW, Australia
| | - David K. Ryugo
- Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
- School of Medical Sciences, University of New South Wales, Kensington, NSW, Australia
- Department of Otolaryngology, Head, Neck and Skull Base Surgery, St. Vincent’s Hospital, Darlinghurst, NSW, Australia
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Maraslioglu-Sperber A, Pizzi E, Fisch JO, Kattler K, Ritter T, Friauf E. Molecular and functional profiling of cell diversity and identity in the lateral superior olive, an auditory brainstem center with ascending and descending projections. Front Cell Neurosci 2024; 18:1354520. [PMID: 38846638 PMCID: PMC11153811 DOI: 10.3389/fncel.2024.1354520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Accepted: 03/15/2024] [Indexed: 06/09/2024] Open
Abstract
The lateral superior olive (LSO), a prominent integration center in the auditory brainstem, contains a remarkably heterogeneous population of neurons. Ascending neurons, predominantly principal neurons (pLSOs), process interaural level differences for sound localization. Descending neurons (lateral olivocochlear neurons, LOCs) provide feedback into the cochlea and are thought to protect against acoustic overload. The molecular determinants of the neuronal diversity in the LSO are largely unknown. Here, we used patch-seq analysis in mice at postnatal days P10-12 to classify developing LSO neurons according to their functional and molecular profiles. Across the entire sample (n = 86 neurons), genes involved in ATP synthesis were particularly highly expressed, confirming the energy expenditure of auditory neurons. Two clusters were identified, pLSOs and LOCs. They were distinguished by 353 differentially expressed genes (DEGs), most of which were novel for the LSO. Electrophysiological analysis confirmed the transcriptomic clustering. We focused on genes affecting neuronal input-output properties and validated some of them by immunohistochemistry, electrophysiology, and pharmacology. These genes encode proteins such as osteopontin, Kv11.3, and Kvβ3 (pLSO-specific), calcitonin-gene-related peptide (LOC-specific), or Kv7.2 and Kv7.3 (no DEGs). We identified 12 "Super DEGs" and 12 genes showing "Cluster similarity." Collectively, we provide fundamental and comprehensive insights into the molecular composition of individual ascending and descending neurons in the juvenile auditory brainstem and how this may relate to their specific functions, including developmental aspects.
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Affiliation(s)
- Ayse Maraslioglu-Sperber
- Animal Physiology Group, Department of Biology, University of Kaiserslautern-Landau, Kaiserslautern, Germany
| | - Erika Pizzi
- Animal Physiology Group, Department of Biology, University of Kaiserslautern-Landau, Kaiserslautern, Germany
| | - Jonas O. Fisch
- Animal Physiology Group, Department of Biology, University of Kaiserslautern-Landau, Kaiserslautern, Germany
| | - Kathrin Kattler
- Genetics/Epigenetics Group, Department of Biological Sciences, Saarland University, Saarbrücken, Germany
| | - Tamara Ritter
- Animal Physiology Group, Department of Biology, University of Kaiserslautern-Landau, Kaiserslautern, Germany
| | - Eckhard Friauf
- Animal Physiology Group, Department of Biology, University of Kaiserslautern-Landau, Kaiserslautern, Germany
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Haragopal H, Mellott JG, Dhar M, Kanel A, Mafi A, Tokar N, Winters BD. Tonotopic distribution and inferior colliculus projection pattern of inhibitory and excitatory cell types in the lateral superior olive of mice. J Comp Neurol 2023; 531:1381-1388. [PMID: 37436768 DOI: 10.1002/cne.25515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 05/26/2023] [Accepted: 06/10/2023] [Indexed: 07/13/2023]
Abstract
The principal neurons (PNs) of the lateral superior olive nucleus (LSO) are an important component of mammalian brainstem circuits that compare activity between the two ears and extract intensity and timing differences used for sound localization. There are two LSO PN transmitter types, glycinergic and glutamatergic, which also have different ascending projection patterns to the inferior colliculus (IC). Glycinergic LSO PNs project ipsilaterally while glutamatergic one's projections vary in laterality by species. In animals with good low-frequency hearing (<3 kHz) such as cats and gerbils, glutamatergic LSO PNs have both ipsilateral and contralateral projections; however, rats that lack this ability only have the contralateral pathway. Additionally, in gerbils, the glutamatergic ipsilateral projecting LSO PNs are biased to the low-frequency limb of the LSO suggesting this pathway may be an adaptation for low-frequency hearing. To further test this premise, we examined the distribution and IC projection pattern of LSO PNs in another high-frequency specialized species using mice by combining in situ hybridization and retrograde tracer injections. We observed no overlap between glycinergic and glutamatergic LSO PNs confirming they are distinct cell populations in mice as well. We found that mice also lack the ipsilateral glutamatergic projection from LSO to IC and that their LSO PN types do not exhibit pronounced tonotopic biases. These data provide insights into the cellular organization of the superior olivary complex and its output to higher processing centers that may underlie functional segregation of information.
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Affiliation(s)
- Hariprakash Haragopal
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, Ohio, USA
| | - Jeffrey G Mellott
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, Ohio, USA
- Brain Health Research Institute, Kent State University, Kent, Ohio, USA
| | - Matasha Dhar
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, Ohio, USA
| | - Alinea Kanel
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, Ohio, USA
| | - Amir Mafi
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, Ohio, USA
| | - Nick Tokar
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, Ohio, USA
| | - Bradley D Winters
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, Ohio, USA
- Brain Health Research Institute, Kent State University, Kent, Ohio, USA
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Koehler CC, Almassri LS, Tokar N, Mafi AM, O’Hara MJ, Young JW, Mellott JG. Age-related Changes of GAD1 mRNA Expression in the Central Inferior Colliculus. TRANSLATIONAL MEDICINE OF AGING 2023; 7:20-32. [PMID: 38111912 PMCID: PMC10727507 DOI: 10.1016/j.tma.2023.04.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2023] Open
Abstract
Encoding sounds with a high degree of temporal precision is an essential task for the inferior colliculus (IC) to perform and maintain the accurate processing of sounds and speech. However, the age-related reduction of GABAergic neurotransmission in the IC interrupts temporal precision and likely contributes to presbycusis. As presbycusis often manifests at high or low frequencies specifically, we sought to determine if the expression of mRNA for glutamic decarboxylase 1 (GAD1) is downregulated non-uniformly across the tonotopic axis or cell size range in the aging IC. Using single molecule in situ fluorescent hybridization across young, middle age and old Fisher Brown Norway rats (an aging model that acquires low frequency presbycusis) we quantified individual GAD1 mRNA in small, medium and large GABAergic cells. Our results demonstrate that small GABAergic cells in low frequency regions had ~58% less GAD1 in middle age and continued to decline into old age. In contrast, the amount of GAD1 mRNA in large cells in low frequency regions significantly increased with age. As several studies have shown that downregulation of GAD1 decreases the release of GABA, we interpret our results in two ways. First, the onset of presbycusis may be driven by small GABAergic cells downregulating GAD1. Second, as previous studies demonstrate that GAD67 expression is broadly downregulated in the old IC, perhaps the translation of GAD1 to GAD67 is interrupted in large GABAergic IC cells during aging. These results point to a potential genetic mechanism explaining reduced temporal precision in the aging IC, and in turn, presbycusis.
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Affiliation(s)
- Christina C. Koehler
- Department of Anatomy and Neurobiology Northeast Ohio Medical University Rootstown, OH USA
| | - Laila S. Almassri
- Department of Anatomy and Neurobiology Northeast Ohio Medical University Rootstown, OH USA
| | - Nick Tokar
- Department of Anatomy and Neurobiology Northeast Ohio Medical University Rootstown, OH USA
| | - Amir M. Mafi
- The Ohio State College of Medicine The Ohio State Columbus, OH USA
| | - Mitchell J. O’Hara
- Department of Anatomy and Neurobiology Northeast Ohio Medical University Rootstown, OH USA
| | - Jesse W. Young
- Department of Anatomy and Neurobiology Northeast Ohio Medical University Rootstown, OH USA
| | - Jeffrey G. Mellott
- Department of Anatomy and Neurobiology Northeast Ohio Medical University Rootstown, OH USA
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Haragopal H, Winters BD. Principal neuron diversity in the murine lateral superior olive supports multiple sound localization strategies and segregation of information in higher processing centers. Commun Biol 2023; 6:432. [PMID: 37076594 PMCID: PMC10115857 DOI: 10.1038/s42003-023-04802-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 04/04/2023] [Indexed: 04/21/2023] Open
Abstract
Principal neurons (PNs) of the lateral superior olive nucleus (LSO) in the brainstem of mammals compare information between the two ears and enable sound localization on the horizontal plane. The classical view of the LSO is that it extracts ongoing interaural level differences (ILDs). Although it has been known for some time that LSO PNs have intrinsic relative timing sensitivity, recent reports further challenge conventional thinking, suggesting the major function of the LSO is detection of interaural time differences (ITDs). LSO PNs include inhibitory (glycinergic) and excitatory (glutamatergic) neurons which differ in their projection patterns to higher processing centers. Despite these distinctions, intrinsic property differences between LSO PN types have not been explored. The intrinsic cellular properties of LSO PNs are fundamental to how they process and encode information, and ILD/ITD extraction places disparate demands on neuronal properties. Here we examine the ex vivo electrophysiology and cell morphology of inhibitory and excitatory LSO PNs in mice. Although overlapping, properties of inhibitory LSO PNs favor time coding functions while those of excitatory LSO PNs favor integrative level coding. Inhibitory and excitatory LSO PNs exhibit different activation thresholds, potentially providing further means to segregate information in higher processing centers. Near activation threshold, which may be physiologically similar to the sensitive transition point in sound source location for LSO, all LSO PNs exhibit single-spike onset responses that can provide optimal time encoding ability. As stimulus intensity increases, LSO PN firing patterns diverge into onset-burst cells, which can continue to encode timing effectively regardless of stimulus duration, and multi-spiking cells, which can provide robust individually integrable level information. This bimodal response pattern may produce a multi-functional LSO which can encode timing with maximum sensitivity and respond effectively to a wide range of sound durations and relative levels.
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Affiliation(s)
- Hariprakash Haragopal
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, OH, USA
| | - Bradley D Winters
- Department of Anatomy and Neurobiology and Hearing Research Group, Northeast Ohio Medical University, Rootstown, OH, USA.
- Brain Health Research Institute, Kent State University, Kent, OH, USA.
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Williams IR, Filimontseva A, Connelly CJ, Ryugo DK. The lateral superior olive in the mouse: Two systems of projecting neurons. Front Neural Circuits 2022; 16:1038500. [PMID: 36338332 PMCID: PMC9630946 DOI: 10.3389/fncir.2022.1038500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 09/29/2022] [Indexed: 01/24/2023] Open
Abstract
The lateral superior olive (LSO) is a key structure in the central auditory system of mammals that exerts efferent control on cochlear sensitivity and is involved in the processing of binaural level differences for sound localization. Understanding how the LSO contributes to these processes requires knowledge about the resident cells and their connections with other auditory structures. We used standard histological stains and retrograde tracer injections into the inferior colliculus (IC) and cochlea in order to characterize two basic groups of neurons: (1) Principal and periolivary (PO) neurons have projections to the IC as part of the ascending auditory pathway; and (2) lateral olivocochlear (LOC) intrinsic and shell efferents have descending projections to the cochlea. Principal and intrinsic neurons are intermixed within the LSO, exhibit fusiform somata, and have disk-shaped dendritic arborizations. The principal neurons have bilateral, symmetric, and tonotopic projections to the IC. The intrinsic efferents have strictly ipsilateral projections, known to be tonotopic from previous publications. PO and shell neurons represent much smaller populations (<10% of principal and intrinsic neurons, respectively), have multipolar somata, reside outside the LSO, and have non-topographic, bilateral projections. PO and shell neurons appear to have widespread projections to their targets that imply a more diffuse modulatory function. The somata and dendrites of principal and intrinsic neurons form a laminar matrix within the LSO and share quantifiably similar alignment to the tonotopic axis. Their restricted projections emphasize the importance of frequency in binaural processing and efferent control for auditory perception. This study addressed and expanded on previous findings of cell types, circuit laterality, and projection tonotopy in the LSO of the mouse.
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Affiliation(s)
- Isabella R. Williams
- Garvan Institute of Medical Research, Darlinghurst, NSW, Australia,School of Medical Sciences, University of New South Wales, Kensington, NSW, Australia,*Correspondence: Isabella R. Williams,
| | | | - Catherine J. Connelly
- Garvan Institute of Medical Research, Darlinghurst, NSW, Australia,School of Medical Sciences, University of New South Wales, Kensington, NSW, Australia
| | - David K. Ryugo
- Garvan Institute of Medical Research, Darlinghurst, NSW, Australia,School of Medical Sciences, University of New South Wales, Kensington, NSW, Australia,Department of Otolaryngology-Head, Neck and Skull Base Surgery, St. Vincent’s Hospital, Darlinghurst, NSW, Australia
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