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.