Neuromodulation by mGluRs in Sound Localization Circuits in the Auditory Brainstem

Abstract

The ability of humans and animals to localize the source of a sound in a complex acoustic environment facilitates communication and survival. Two cues are used for sound localization at horizontal planes, interaural time and level differences (ITD and ILD), which are analyzed by distinct neural circuits in the brainstem. Here, we review the studies on metabotropic glutamate receptor (mGluR)-mediated neuromodulation of both intrinsic and synaptic properties of brainstem neurons in these circuits. Both mammalian and avian animal models have been used, with each having their advantages that are not present in the other. For the mammalian model, we discuss mGluR neuromodulation in the ILD circuit, with an emphasis on the recent discovery of differential modulation of synaptic transmission of different transmitter release modes. For the avian model, we focus on reviewing mGluR neuromodulation in the ITD pathway, with an emphasis on tonotopic distribution and synaptic plasticity of mGluR modulation in coincidence detector neurons. Future works are proposed to further investigate the functions and mechanisms of mGluRs in the sound localization circuits.

Tonotopic differentiation of presynaptic neurotransmitter‐releasing machinery in the auditory brainstem during the prehearing period and its selective deficits in Fmr1 knockout mice

“…Several developmental events on postsynaptic neurons also follow this pattern, and these events are thought to facilitate neuronal responses to their characterized frequencies during both development and maturation. These events include sound frequency‐dependent distribution of potassium channels and their conductance and coupling with Ca 2+ (Adachi et al., 2019; Fukui & Ohmori, 2004; Leao et al., 2006; Li et al., 2001), neuronal modulation by group I metabotropic glutamate receptors (mGluRs) (Goel et al., 2020), postsynaptic localization of scaffold proteins (Goyer et al., 2015), and dendritic arborization patterns (Sanchez et al., 2017; Sanes et al., 1990; Smith & Rubel, 1979).…”