Spontaneous activity of developing neuronal networks can be measured using AM-ester forms of calcium-sensitive indicator dyes. Changes in intracellular calcium, indicating neuronal activation, are detected as transient changes in indicator fluorescence with one- or two-photon imaging. This protocol can be adapted for a range of developmentally-dependent neuronal networks in vitro.
Dawitz, J., Kroon, T., Hjorth, J. J., Meredith, R. M. Functional Calcium Imaging in Developing Cortical Networks. J. Vis. Exp. (56), e3550, doi:10.3791/3550 (2011).