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Spontaneous action potentials were recorded longitudinally for 4–7 weeks from dissociated rat occipital cortex cells cultured on planar multi-electrode plates, during their development from isolated neurons into synaptically connected neuronal networks. Activity typically consisted of generalized bursts lasting up to several seconds, separated by variable epochs of sporadic firing at some of the active sites. These network bursts displayed discharge patterns with age-dependent firing rate profiles, and durations significantly increasing in the 3rd week in vitro and decreasing after about 1 month in vitro, when they evolved into short events with prompt onsets. These findings indicate that after about a month in vitro these cultured neuronal networks have developed a degree of excitability that allows almost instantaneous triggering of generalized discharges. Individual neurons tend to fire in specific and persistent temporal relationships to one another within these network bursts, suggesting that network connectivity maintains a core topology during its development. [Copyright &y& Elsevier]

Abstract: Chronic blockade of actively excitatory glutamatergic synaptic receptors in co-cultured organotypic rodent neocortex explants rapidly leads to a compensatory sensitization of otherwise inactive input channels so as to maintain ongoing action potential bursts. We report here that the homeostatic return of spontaneous, kainate receptor driven, spike discharges is followed by a reciprocal desensitization of blocked AMPA and NMDA receptors, such that the developing network is protected against becoming hyperactive once full synaptic drive is restored. [Copyright &y& Elsevier]