Astrocyte Calcium Signaling Shifts the Polarity of Presynaptic Plasticity

astrocytes have been increasingly acknowledged to play active roles in regulating synaptic transmis-sion and plasticity. Through a variety of metabotropic and ionotropic receptors expressed on their surface, astro-cytes detect extracellular neurotransmitters, and in turn, release gliotransmitters to modify synaptic strength, while they can also alter neuronal membrane excitability by modulating extracellular ionic milieu. Given the seem-ingly large repertoire of synaptic modulation, when, where and how astrocytes interact with synapses remain to be fully understood. Previously, we have identified a role for astrocyte NMDA receptor and L-VGCCs signaling in heterosynaptic presynaptic plasticity and promoting the heterogeneity of presynaptic strengths at hippocampal synapses. Here, we have sought to further clarify the mode by which astrocytes regulate presynaptic plasticity by exploiting a reduced culture system to globally evoke NMDA receptor-dependent presynaptic plasticity. Record-ing from a postsynaptic neuron intracellularly loaded with BAPTA, briefly bath applying NMDA and glycine induces a stable decrease in the rate of spontaneous glutamate release, which requires the presence of astro-cytes and the activation of A1 adenosine receptors. Upon preventing astrocyte calcium signaling or blocking L-VGCCs, NMDA + glycine application triggers an increase, rather than a decrease, in the rate of spontaneous glutamate release, thereby shifting the presynaptic plasticity to promote an increase in strength. Our findings point to a crucial and surprising role of astrocytes in controlling the polarity of NMDA receptor and adenosine -dependent presynaptic plasticity. Such a pivotal mechanism unveils the power of astrocytes in regulating com-putations performed by neural circuits and is expected to profoundly impact cognitive processes.& COPY; 2023 The Author(s). Published by Elsevier Ltd on behalf of IBRO. This is an open access article under the CC BY-NC-ND license (http://crea-tivecommons.org/licenses/by-nc-nd/4.0/).