PT - JOURNAL ARTICLE AU - Zhang, Yao V. AU - Ormerod, Kiel G. AU - Littleton, J. Troy TI - Astrocyte Ca<sup>2+</sup> Influx Negatively Regulates Neuronal Activity AID - 10.1523/ENEURO.0340-16.2017 DP - 2017 Mar 01 TA - eneuro PG - ENEURO.0340-16.2017 VI - 4 IP - 2 4099 - http://www.eneuro.org/content/4/2/ENEURO.0340-16.2017.short 4100 - http://www.eneuro.org/content/4/2/ENEURO.0340-16.2017.full SO - eNeuro2017 Mar 01; 4 AB - Maintenance of neural circuit activity requires appropriate regulation of excitatory and inhibitory synaptic transmission. Recently, glia have emerged as key partners in the modulation of neuronal excitability; however, the mechanisms by which glia regulate neuronal signaling are still being elucidated. Here, we describe an analysis of how Ca2+ signals within Drosophila astrocyte-like glia regulate excitability in the nervous system. We find that Drosophila astrocytes exhibit robust Ca2+ oscillatory activity manifested by fast, recurrent microdomain Ca2+ fluctuations within processes that infiltrate the synaptic neuropil. Unlike the enhanced neuronal activity and behavioral seizures that were previously observed during manipulations that trigger Ca2+ influx into Drosophila cortex glia, we find that acute induction of astrocyte Ca2+ influx leads to a rapid onset of behavioral paralysis and a suppression of neuronal activity. We observe that Ca2+ influx triggers rapid endocytosis of the GABA transporter (GAT) from astrocyte plasma membranes, suggesting that increased synaptic GABA levels contribute to the neuronal silencing and paralysis. We identify Rab11 as a novel regulator of GAT trafficking that is required for this form of activity regulation. Suppression of Rab11 function strongly offsets the reduction of neuronal activity caused by acute astrocyte Ca2+ influx, likely by inhibiting GAT endocytosis. Our data provide new insights into astrocyte Ca2+ signaling and indicate that distinct glial subtypes in the Drosophila brain can mediate opposing effects on neuronal excitability.