Intracellular Astrocyte Calcium Waves In Situ Increase the Frequency of Spontaneous AMPA Receptor Currents in CA1 Pyramidal Neurons

Abstract

Spontaneous neurotransmitter release and activation of group I metabotropic glutamate receptors (mGluRs) each play a role in the plasticity of neuronal synapses. Astrocytes may contribute to short- and long-term synaptic changes by signaling to neurons via these processes. Spontaneous whole-cell AMPA receptor (AMPAR) currents were recorded in CA1 pyramidal cells in situ while evoking Ca 2+increases in the adjacent stratum radiatum astrocytes by uncaging IP 3. Whole-cell patch clamp was used to deliver caged IP 3 and the Ca 2+indicator dye Oregon green BAPTA-1 to astrocytes. Neurons were patch-clamped and filled with Alexa 568 hydrazide dye to visualize their morphological relationship to the astrocyte. On uncaging of IP 3, astrocyte Ca 2+responses reliably propagated as a wave into the very fine distal processes, synchronizing Ca 2+activity within astrocyte microdomains. The intracellular astrocyte Ca 2+wave coincided with a significant increase in the frequency of AMPA spontaneous EPSCs, but with no change in their kinetics. AMPAR current amplitudes were increased as well, but not significantly (p= 0.06). The increased frequency of AMPAR currents was sensitive to the group I mGluR antagonists LY367385 and 2-methyl-6-(phenylethynyl)-pyridine, suggesting that (1) astrocytes released glutamate in response to IP 3 uncaging, and (2) glutamate released by astrocytes activated group I mGluRs to facilitate the release of glutamate from excitatory neuronal presynaptic boutons. These results extend previous studies, which have shown astrocyte modulation of neuronal activity in vitro and suggest that astrocyte-to-neuron signaling in intact tissue may contribute to synaptic plasticity.