Distinct subsynaptic localization of type 1 metabotropic glutamate receptors at glutamatergic and GABAergic synapses in the rodent cerebellar cortex.
Type 1 metabotropic glutamate (mGlu1) receptors play a pivotal role in different forms of synaptic plasticity in the cerebellar cortex, e.g. long-term depression at glutamatergic synapses and rebound potentiation at GABAergic synapses. These various forms of plasticity might depend on the subsynaptic arrangement of the receptor in Purkinje cells that can be regulated by protein-protein interactions. This study investigated, by means of the freeze-fracture replica immunogold labelling method, the subcellular localization of mGlu1 receptors in the rodent cerebellum and whether Homer proteins regulate their subsynaptic distribution. We observed a widespread extrasynaptic localization of mGlu1 receptors and confirmed their peri-synaptic enrichment at glutamatergic synapses. Conversely, we detected mGlu1 receptors within the main body of GABAergic synapses onto Purkinje cell dendrites. Although Homer proteins are known to interact with the mGlu1 receptor C-terminus, we could not detect Homer3, the most abundant Homer protein in the cerebellar cortex, at GABAergic synapses by pre-embedding and post-embedding immunoelectron microscopy. We then hypothesized a critical role for Homer proteins in the peri-junctional localization of mGlu1 receptors at glutamatergic synapses. To disrupt Homer-associated protein complexes, mice were tail-vein injected with the membrane-permeable dominant-negative TAT-Homer1a. Freeze-fracture replica immunogold labelling analysis showed no significant alteration in the mGlu1 receptor distribution pattern at parallel fibre-Purkinje cell synapses, suggesting that other scaffolding proteins are involved in the peri-synaptic confinement. The identification of interactors that regulate the subsynaptic localization of the mGlu1 receptor at neurochemically distinct synapses may offer new insight into its trafficking and intracellular signalling.
Department of Pharmacology, Innsbruck Medical University, Innsbruck, Austria.
Mahnaz
M
Mansouri
Yu
Y
Kasugai
Yugo
Y
Fukazawa
Federica
F
Bertaso
Fabrice
F
Raynaud
Julie
J
Perroy
Laurent
L
Fagni
Walter A
WA
Kaufmann
Masahiko
M
Watanabe
Ryuichi
R
Shigemoto
Francesco
F
Ferraguti
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism; D002525:Cerebellar Cortex / Q000378:metabolism* / Q000648:ultrastructure; D018698:Glutamic Acid / Q000378:metabolism*; D000072233:Homer Scaffolding Proteins; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008854:Microscopy, Electron; D011689:Purkinje Cells / Q000378:metabolism / Q000648:ultrastructure; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002352:Carrier Proteins; D000072233:Homer Scaffolding Proteins; C000606627:Homer3 protein, mouse; C000606628:Homer3 protein, rat; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid
Homer; Purkinje cell; freeze-fracture; parallel fibres