FIGURE 4.

Tonic GABAergic currents can promote epileptiform activity in the early postnatal hippocampus. (A) Whole cell recording of a CA3 pyramidal neuron in the P4–7 hippocampus. The experiment was performed in the continuous presence of 40 μM dl-2-amino-5-phosphopentanoic acid (APV), 10 μM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and 1 μM gabazine (GBZ) to block synaptic components. Note that bath application of 1 μM 4,5,6,7-tetrahydroisooxazolo[5,4-c]pyridin-3-ol hydrochloride (THIP) induced a small tonic current and that the GABA_A antagonist picrotoxin uncovers a tonic GABAergic component. (B) Field potential recording illustrating that bath application of 1 μMTHIP in low-Mg²⁺ solution induced epileptiform discharges. (C) Statistical analysis demonstrating that 1 μMTHIP significantly increased the incidence of epileptiform discharges (compared to the control condition in low-Mg²⁺ solution). This proconvulsive THIP effect was prevented in the presence of the α5 selective antagonist L-655,708. Modified from Kolbaev et al. (2012).