Differential projections from the cochlear nucleus to the inferior colliculus in the mouse

David K Ryugo; Giedre Milinkeviciute

doi:10.3389/fncir.2023.1229746

Differential projections from the cochlear nucleus to the inferior colliculus in the mouse

Front Neural Circuits. 2023 Jul 24:17:1229746. doi: 10.3389/fncir.2023.1229746. eCollection 2023.

Authors

David K Ryugo^{1

2

3}, Giedre Milinkeviciute^{1

2}

Affiliations

¹ Garvan Institute of Medical Research, Darlinghurst, NSW, Australia.
² School of Biomedical Sciences, University of New South Wales, Kensington, NSW, Australia.
³ Department of Otolaryngology, Head and Neck and Skull Base Surgery, St. Vincent's Hospital, Darlinghurst, NSW, Australia.

Abstract

The cochlear nucleus (CN) is often regarded as the gateway to the central auditory system because it initiates all ascending pathways. The CN consists of dorsal and ventral divisions (DCN and VCN, respectively), and whereas the DCN functions in the analysis of spectral cues, circuitry in VCN is part of the pathway focused on processing binaural information necessary for sound localization in horizontal plane. Both structures project to the inferior colliculus (IC), which serves as a hub for the auditory system because pathways ascending to the forebrain and descending from the cerebral cortex converge there to integrate auditory, motor, and other sensory information. DCN and VCN terminations in the IC are thought to overlap but given the differences in VCN and DCN architecture, neuronal properties, and functions in behavior, we aimed to investigate the pattern of CN connections in the IC in more detail. This study used electrophysiological recordings to establish the frequency sensitivity at the site of the anterograde dye injection for the VCN and DCN of the CBA/CaH mouse. We examined their contralateral projections that terminate in the IC. The VCN projections form a topographic sheet in the central nucleus (CNIC). The DCN projections form a tripartite set of laminar sheets; the lamina in the CNIC extends into the dorsal cortex (DC), whereas the sheets to the lateral cortex (LC) and ventrolateral cortex (VLC) are obliquely angled away. These fields in the IC are topographic with low frequencies situated dorsally and progressively higher frequencies lying more ventrally and/or laterally; the laminae nestle into the underlying higher frequency fields. The DCN projections are complementary to the somatosensory modules of layer II of the LC but both auditory and spinal trigeminal terminations converge in the VLC. While there remains much to be learned about these circuits, these new data on auditory circuits can be considered in the context of multimodal networks that facilitate auditory stream segregation, signal processing, and species survival.

Keywords: anatomy; auditory; circuits; dextran amine; hearing; projections; tonotopy.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Auditory Pathways / physiology
Cochlear Nucleus* / physiology
Inferior Colliculi* / physiology
Mice
Mice, Inbred CBA
Neurons

Grants and funding

This work was made possible by the following funding sources: NHMRC Grant 1009482 and 1080652; a grant from the Walker Family Foundation; a bequest from Helen Morgan; and donations to the Hearing Research Lab from Charlene and Graham Bradley, Sue and Haydn Daw, and Alan and Lynn Rydge. GM was recipient of a University International Postgraduate Award from the UNSW Australia. The donors had no role in the direction, analysis, or publication of this work.