GABAA receptor-mediated modulation of neuronal activity propagation upon tetanic stimulation in rat hippocampal slices.

Tetanic stimulation (100 Hz), which can induce long-term potentiation in synaptic connections in the hippocampal CA1 region, causes γ-aminobutyric acid (GABA)(A) receptor-mediated long-lasting depolarization of postsynaptic neurons. However, it is not clear how this stimulation modulates neuronal activity propagation. We studied tetanic burst-induced neuronal responses in the hippocampal CA1 region by using optical-recording methods employing a voltage-sensitive dye and focused on GABA(A) receptor-mediated modulation. We observed that burst stimulation induced long-lasting depolarization and progressive decrease in individual excitatory postsynaptic potentials (EPSPs). Both these effects were suppressed by picrotoxin, a GABA(A) receptor antagonist. Under whole-cell voltage-clamp conditions, we observed a long-lasting inhibitory current (IPSC) and a prominent progressive decrease in the amplitude of the excitatory postsynaptic current (EPSC). Further, picrotoxin inhibited the IPSC and the progressive decrease in EPSC. The optically recorded long-lasting depolarization and progressive decrease of EPSPs were strongly dependent on the distance between the recording electrode and the stimulation site. Optical recordings performed across a wide swatch of CA1 revealed that the decrease in activity propagation was followed by facilitation of propagation after recovery and that this facilitation also depended on GABA(A) receptors. Intense activation of GABA(A) receptors is a key factor shaping the spatiotemporal patterns of high-frequency stimulation-induced responses in the CA1 region.