The striatum plays an important role in linking cortical activity to basal ganglia outputs. We conducted the Ca²⁺ imaging study to investigate the spontaneous activities of the striatum. Corticostriatal slices of 10-25 days old Sprague Dawley rats were stained with Fura-PE3-AM to measure intracellular Ca²⁺ concentration ([Ca²⁺]_i) using a cooled-CCD imaging system. Long lasting spontaneous [Ca²⁺]_i transients, which lasted up to about 250 s, were observed. Most cells exhibited irregular frequencies, but some exhibited oscillatory feature. A pairwise correlation analysis revealed that some cells appear to belong to a correlated network. Administration of TTX or of CNQX + AP5 did not block the [Ca²⁺]_i transients. Therefore, the action potentials and the excitatory synaptic inputs in the striatal network were not involved in induction of the [Ca²⁺]_i transients. In contrast, the number of active cells, which exhibited the [Ca²⁺]_i transients, was greatly reduced by the intracellular Ca²⁺ store depletor, thapsigargin, and was reduced little by the administration of the Ca²⁺-free saline. Therefore, the intracellular Ca²⁺ store is likely to contribute to the [Ca²⁺]_i transients. In the mouse, which expressed green fluorescent protein (GFP) in astrocytes (GFAP-GFP mouse), both the GFP positive cells and the GFP negative cells exhibited the [Ca²⁺]_i transients. These results suggested that both astrocytes and neurons may exhibit the long lasting spontaneous [Ca²⁺]_i transients in the striatum. [J Physiol Sci. 2006;56 Suppl:S83]