Spontaneous Calcium Dynamics in the Development of Cultured Cortical Networks

Spontaneous electrical activity and intracellular calcium dynamics in dense cultures of rat cortical networks were simultaneously observed by using microelectrode array (MEA) and optical imaging system. At around one-week-cultures, periodical synchronized bursts, which are characteristic features of cultured cortical networks, were observed, and these synchronized bursts were followed by synchronized intracellular calcium transients among neural cells. After three weeks cultures, synchronized intracellular calcium transients were rarely observed in the cultured cortical networks although neurons showed distinct electrical activity with high frequency. As for the intermediate stage between these two states, we found slow, radial propagation of intracellular calcium waves were observed independent of the electrical activity of neural cells at around two-weeks cultures. The carriers of these calcium waves were suggested to be astrocytes from the result of pharmacological treatments of these cultured cortical networks. These results indicate that the dynamics of intracellular calcium in cortical networks changes depending on the developmental stages of cortical tissues, and astrocytes have characteristic roles in the development of functional cortical tissues as well as the spontaneous electrical activity of neurons.