, 2003). Because of their early firing, we reasoned that HS cells might have a pivotal role in GFO emergence by synchronizing

their target interneurons (i.e., GABA neurons with exclusive local projections) into high-frequency GSK1210151A manufacturer firing, thus generating field GFOs. The firing patterns of the different cell types during GFOs are consistent with this hypothesis. If HS cells play a leading role in synchronizing their targets, we propose the following scheme: (1) a progressive recruitment of HS cells, because transient network events may involve a progressive recruitment of leading cells (de la Prida et al., 2006); (2) a depolarizing action of GABA onto interneurons; and (3) a recruitment of the interneurons (with exclusive local projections) by the HS cells. Finally, if a causal link exists between HS firing and GFO emergence, preventing HS cell firing should abolish GFOs. We directly tested these CCI-779 cell line proposals. We first investigated the possibility of a buildup mechanism among interconnected HS cells. We analyzed the firing behavior of eleven HS cell pairs (four reciprocal and seven unidirectional connections; Figures S3A and S3B). Before GFO genesis, HS cell firing started to accelerate at a mean instantaneous frequency of 28 ± 11 Hz until an abrupt transition to high-frequency firing

occurred within 150 ± 65 ms before GFO onset (Figure 3B). In keeping with a progressive recruitment of HS cells, there was a regular increase in GABAergic currents received by both HS cells and interneurons (Figure 3B3). Dual recordings revealed until that HS cells were connected together and to other GABA neurons (four unidirectional HS to O-LM connections, three HS to O-LM reciprocal connections; Figures S3A and S3B). During the buildup process, the frequency of GABA currents remained low, consistent with the low-frequency firing of HS cells before

their transition to high-frequency firing (Figure 3B3). The switch to high-frequency firing of HS cells correlated with the high-frequency GABA currents received by the interneurons (Figure 3B3). Those results are thus in favor of a progressive recruitment of HS cells. We then analyzed the nature of the neurotransmission between HS cells and their targets in normal artificial cerebro-spinal fluid (four reciprocal and seven unidirectional HS pairs, four unidirectional HS to O-LM connections, three HS to O-LM reciprocal connections; Figure S3A and S3B). The neurotransmission was extremely reliable at these synapses (1.0 release probability; n = 25 connections). Intracellular chloride concentration increases in epileptic conditions in the immature brain, rendering GABA strongly excitatory (Dzhala et al., 2010). By using noninvasive measurements of the resting membrane potential and the reversal potential of chloride in different classes of GABA neurons, we found that ECl was 19.1mV ± 1.