Using single-cell and multiunit electrophysiology in layer III entorhinal cortex and disinhibited hippocampal CA3 slices it has been demonstrated that the balancing of the up-down activity is characterized by both GABA_A and GABA_B mechanisms. In the present communication we report novel results obtained by multi-electrode array simultaneous recordings from reverberating postnatal neocortical networks which contain 19.2 ± 1.4% GABAergic neurons, typical of intact tissue. We observed that in each spontaneous active-state the total number of spikes in identified clusters of excitatory and inhibitory neurons is almost equal, thus suggesting a balanced average activity. Otherwise during the early up-state phase the number of excitatory spikes is greater (n = 1067) than inhibitory ones (n = 305), therefore indicating an early unbalance.

Some drugs resulted to affect up- and/or down-states with different IC₅₀s, providing evidence that various mechanisms are involved. Using selective modulators we demonstrate that up- and down- network states are robustly governed, not only by GABA_A and GABA_B mechanisms, but also by others such as GAT-1-mediated uptake, I_h, INa_P and I_M ion channel activity. These results should reinforce not only the role of synchrony in CNS networks, but also the recognized analogies between the Hodgkin–Huxley action potential and the population bursts as basic mechanisms for originating membrane excitability and CNS network synchronization, respectively.