Functional architecture of the synaptic transducers at a central glutamatergic synapse

Abstract

SummaryNeuronal synapses transduce information via the consecutive action of three transducers: voltage-gated Ca2+-channels, fusion-competent synaptic vesicles, and postsynaptic receptors. Their physical distance is thought to influence the speed and efficiency of neurotransmission. However, technical limitations have hampered resolving their nanoscale arrangement. Here, we developed a new method for live-labeling proteins for electron microscopy (EM), revealing that release-competent vesicles preferentially align with Ca2+-channels and postsynaptic AMPA receptors within 20-30 nm and thereby forming a transsynaptic tripartite nanocomplex. Using functional EM, we show that single action potentials cause vesicles within the nanocomplex to fuse with a 50% probability. The loss of the presynaptic scaffold disrupts the formation of the tripartite transducers. Strikingly, the forced transsynaptic alignment of the Ca2+-channel subunit α2δ1 and AMPA receptors suffice to restore neurotransmission in a scaffold lacking synapse. Our results demonstrate a synaptic transducer nanocomplex that actively contributes to the organization of central synapses.

Asynchronous glutamate exocytosis is enhanced in low release probability synapses and is widely dispersed across the active zone

“…Based on the available electron microscopy data 3,4,12,31,32 , we considered a typical active zone of an area S = 0.12 µm 2 , that contained two VGCCs clusters (located at the active zone periphery) and rel N = 12 of vesicular release cites that were randomly distributed across the active zone (Fig. 4C,D).…”

“…4B-G and Methods). The model was based on the recent functional electron microscopy and single-molecule localisation data showing that presynaptic VGCCs, synchronous release sites and postsynaptic AMPA receptors colocalise within 20 -30 nm distance and that AMPA receptor clusters preferentially localise to the periphery of the postsynaptic density/active zone [2][3][4]12 . The model reproduced both a greater asynchronous release fraction at low release probability boutons (Fig.…”

“…At first sight, our findings contradict the electron microscopy studies, which demonstrated that asynchronous release loci are more biased towards the centre of the active zone 4,12 . Synchronous release events are expected to concentrate around VGCC clusters, which are predominantly located at the periphery of the active zone [2][3][4] (Fig. 4C).…”