Excitatory and inhibitory receptors utilize distinct post- and trans-synaptic mechanisms in vivo.

Taisuke Miyazaki,Tokiwa Yamasaki,Matthijs Verhage,Susumu Tomita,Pablo E Castillo,Kotaro Konno,Coralie Berthoux,Yoav Noam,Masahiko Watanabe,Megumi Morimoto-Tomita

doi:10.7554/elife.59613

Abstract

Ionotropic neurotransmitter receptors at postsynapses mediate fast synaptic transmission upon binding of the neurotransmitter. Post- and trans-synaptic mechanisms through cytosolic, membrane, and secreted proteins have been proposed to localize neurotransmitter receptors at postsynapses. However, it remains unknown which mechanism is crucial to maintain neurotransmitter receptors at postsynapses. In this study, we ablated excitatory or inhibitory neurons in adult mouse brains in a cell-autonomous manner. Unexpectedly, we found that excitatory AMPA receptors remain at the postsynaptic density upon ablation of excitatory presynaptic terminals. In contrast, inhibitory GABAA receptors required inhibitory presynaptic terminals for their postsynaptic localization. Consistent with this finding, ectopic expression at excitatory presynapses of neurexin-3 alpha, a putative trans-synaptic interactor with the native GABAA receptor complex, could recruit GABAA receptors to contacted postsynaptic sites. These results establish distinct mechanisms for the maintenance of excitatory and inhibitory postsynaptic receptors in the mature mammalian brain.

Highlights

Fast excitatory and inhibitory synaptic transmissions in the mature brain are mostly mediated by ionotropic AMPA-type glutamate receptors (AMPARs) and GABAA receptors (GABAARs), respectively
Selective removal of granule cells and Purkinje cells in the mature brain The cerebellum consists of the molecular layer (ML), the Purkinje cell layer (PCL), the granular layer (GL), and deep cerebellar nuclei (DCN) in the white matter (WM) (Figure 1A)
We found that uncaging glutamate-evoked excitatory postsynaptic currents were undistinguishable in control and Granule cells (GCs) mice (Control, 32 ± 3.9 pA, n = 6 from three mice; GC, 30 ± 3.9 pA, n = 7 from four mice; p = 0.8037, unpaired t-test), and these responses were abolished by the AMPAR antagonist NBQX (Figure 2G, H)

Summary

Introduction

Fast excitatory and inhibitory synaptic transmissions in the mature brain are mostly mediated by ionotropic AMPA-type glutamate receptors (AMPARs) and GABAA receptors (GABAARs), respectively. The specificity of the neuronal loss was later improved with genetic and pharmacological approaches, such as by expression of a toxin gene or exogenous receptor/enzyme expression combined with agonist administration (Gray et al, 2010; Palmiter et al, 1987; Watanabe et al, 1998; Yang et al., 2013). To date, these methods have been limited in their ability to uncover mechanisms of postsynaptic receptor localization mainly due to pleiotropic effects. We took advantage of the cell-autonomous elimination observed in Stxbp homozygous neurons (Dudok et al, 2011; Heeroma et al, 2004) to investigate the machinery responsible for maintaining neurotransmitter receptors at postsynapses

Results

Discussion

Materials and methods