Development of low magnesium-induced spontaneous synchronized bursting and GABAergic modulation in cultured rat neocortical neurons.

Development of spontaneous synchronized bursting in the early stages of rat neocortical neuronal cultures was studied by whole-cell and extracellular recordings. Neocortical neurons from rat embryos were cultured on planar electrode arrays, and low Mg(2+)-induced spontaneous activity was recorded from 5 to 16 days in vitro (DIV). At 5-6 DIV the current synchronized to the bursting had only a slow component lasting 3-5 s, whereas in older cultures a fast transient component was dominant. A gamma-aminobutyric acid (GABA)A receptor antagonist, bicuculline methiodide, had little effect on the spontaneous activity at 5-6 DIV, whereas in older cultures it had a marked effect on the slow current component. These results suggest a role of GABAergic transmission in the development of synchronized activities.