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. 2020 Sep 22;32(12):108182.
doi: 10.1016/j.celrep.2020.108182.

Local Efficacy of Glutamate Uptake Decreases with Synapse Size

Michel K Herde  1 , Kirsten Bohmbach  1 , Cátia Domingos  1 , Natascha Vana  2 , Joanna A Komorowska-Müller  1 , Stefan Passlick  1 , Inna Schwarz  3 , Colin J Jackson  4 , Dirk Dietrich  2 , Martin K Schwarz  3 , Christian Henneberger  5
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Free article

Local Efficacy of Glutamate Uptake Decreases with Synapse Size

Michel K Herde et al. Cell Rep. .
Free article

Abstract

Synaptically released glutamate is largely cleared by glutamate transporters localized on perisynaptic astrocyte processes. Therefore, the substantial variability of astrocyte coverage of individual hippocampal synapses implies that the efficacy of local glutamate uptake and thus the spatial fidelity of synaptic transmission is synapse dependent. By visualization of sub-diffraction-limit perisynaptic astrocytic processes and adjacent postsynaptic spines, we show that, relative to their size, small spines display a stronger coverage by astroglial transporters than bigger neighboring spines. Similarly, glutamate transients evoked by synaptic stimulation are more sensitive to pharmacological inhibition of glutamate uptake at smaller spines, whose high-affinity N-methyl-D-aspartate receptors (NMDARs) are better shielded from remotely released glutamate. At small spines, glutamate-induced and NMDAR-dependent Ca2+ entry is also more strongly increased by uptake inhibition. These findings indicate that spine size inversely correlates with the efficacy of local glutamate uptake and thereby likely determines the probability of synaptic crosstalk.

Keywords: astrocyte morphology; astrocytes; expansion microscopy; glutamate uptake; hippocampus; multiphoton imaging; spine morphology.

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Conflict of interest statement

Declaration of Interests The authors declare no competing interests.

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