Anatomy and Physiology of Metabotropic Glutamate Receptors in Mammalian and Avian Auditory System.

Yong Lu

doi:10.24966/tap-7752/100001

Abstract

Glutamate, as the major excitatory neurotransmitter used in the vertebrate brain, activates ionotropic and metabotropic glutamate receptors (iGluRs and mGluRs), which mediate fast and slow neuronal actions, respectively. mGluRs play important modulatory roles in many brain areas, forming potential targets for drugs developed to treat brain disorders. Here, we review studies on mGluRs in the mammalian and avian auditory system. Although anatomical expression of mGluRs in the cochlear nucleus has been well characterized, data for other auditory nuclei await more systematic investigations especially at the electron microscopy level. The physiology of mGluRs has been extensively studied using in vitro brain slice preparations, with a focus on the auditory circuitry in the brainstem. These in vitro physiological studies have demonstrated that mGluRs participate in synaptic transmission, regulate ionic homeostasis, induce synaptic plasticity, and maintain the balance between Excitation and Inhibition (E/I) in a variety of auditory structures. However, the modulatory roles of mGluRs in auditory processing remain largely unclear at the system and behavioral levels, and the functions of mGluRs in auditory disorders remain entirely unknown.

Highlights

MGluRs were discovered more than 30 years ago [1,2,3]
Based on our observation that mGluRs control the inhibitory strength in Nucleus Magnocellularis (NM) neurons to prevent generation of GABAinduced spike that are not phase-locked to the excitatory input from the auditory nerve, we propose that mGluRs enhance the phase-locking fidelity of NM neurons and improve coincidence detection in Nucleus Laminaris (NL) neurons
We mainly reviewed the anatomy and physiology of mGluRs at cellular level in both mammalian and avian auditory systems

Summary

Introduction

MGluRs were discovered more than 30 years ago [1,2,3]. To date, eight members of mGluRs have been identified and divided into three major groups (group I: mGluR1 and 5; group II: mGluR2 and 3; and group III: mGluR4, 6, 7, and 8) based on their amino acid sequence, pharmacological properties, and signaling transduction pathways [4]. mGluRs are expressed widely in the peripheral and central nervous system, exhibit a high degree of homologyTang and Lu across different animal species, and exert neuromodulatory actions via multiple signaling pathways [5,6,7]. Of the mGluRs shown to express in the cochlea, physiological evidence for involvement of group I mGluR1 and group III mGluR7 in neurotransmission at the synapses between hair cells and the dendrites of spiral ganglion neurons, as well as mGluR II on the efferent input to IHCs, has been reported.

Results

Conclusion