Astrocytes intimately contact synapses with their fine astrocyte processes regulating synaptic functions. Fine astrocytic processes can receive information from synapses and also transmit their information to synapses. Thus, astrocytes may regulate synapses through bidirectional information processing. Recently, we found astrocytes regulate synapse remodelling in primary somatosensory cortex in Ca2+ dependent manner, contributing to the induction of aberrant sensation in neuropathic pain model mice. It has been thought that Ca2+ dynamics at fine astrocytic processes regulate synaptic functions/neuronal excitability. However, its dynamic interaction between neurons and astrocytes is largely unknown. To this end, we took viral introduction of red fluorescent genetically encoded Ca2+ indicators (GECI) and green fluorescent GECI into neurons and astrocytes, respectively. We have succeeded to monitor both spontaneous and evoked Ca2+ signals simultaneously from neurons and astrocytes in the hippocampus in situ. Enhancement of astrocytic Ca2+ signals by selective manipulation of astrocytic receptors altered dendritic Ca2+ excitation. The approach described here may provide useful information on bidirectional information processing at synapses.