Figure 4. GABA_AR-induced effect on motoneuron membrane potential at E13.5, E16.5 and P0.

A brief pulse of depolarizing current (i) is injected into recorded motoneurons in order to bring the membrane potential above spike threshold. Then, a brief pressure application of isoguvacine (100 μm, 20 ms, 4 p.s.i.) is used to activate GABA_AR. A, at E13.5, at resting membrane potential (V_rest, A1), either depolarizing current or application of isoguvacine elicits a depolarization, on top of which a spike is generated. The amplitude of this depolarization is increased when the membrane potential is held (V_h) at −70 mV and an action potential is still triggered. B, at E16.5, a depolarizing pulse of current still elicits an action potential whatever the membrane potential (B1, B2) whereas the stimulation of GABA_AR evokes a hyperpolarization at V_h−50 mV (B1) and a depolarization at V_rest (B2). C, at birth the injected current triggers, at threshold level, a train of action potentials (C1, C2) whereas the application of isoguvacine still hyperpolarizes the membrane potential at V_h−50 mV (C1) but does not alter the membrane potential at V_h−70 mV (C2).