Local stimulation induced GABAergic response in rat striatal slice preparations: intracellular recordings on QX-314 injected neurons.

Gamma-aminobutyric acid (GABA)ergic responses evoked by electrical stimulation in the neostriatal slice preparation were studied in neurons injected intracellularly with Na-conductance blocker QX-314. Local stimulation elicited depolarizing postsynaptic potentials (DPSPs) in the QX-314-injected neurons when the membrane potential was more negative than -60 mV. When DPSPs were minimized by depolarizing current injection in the QX-314-injected neuron, hyperpolarization was clearly observed following local stimulation. The maximum duration of the hyperpolarizing response to strong local stimulation was about 130 ms. The hyperpolarizing response was blocked by the addition of bicuculline or picrotoxin to the Ringer solution. Intracellular Cl- injections produced changes in the pattern of the local stimulation-induced responses; the initial depolarizing response was followed by a relatively large amplitude long duration depolarization. The polarity of the long duration depolarizing response could not be reversed by depolarizing currents which were normally sufficient to reverse the polarity of DPSPs in the neurons without Cl- injection. The application of pentobarbital enhanced the amplitude and the duration of the hyperpolarizing responses. The reversal potential of the pentobarbital-enhanced response was estimated to be -60 mV. On the basis of their reversal potential, sensitivity to injected Cl-, sensitivity to GABA blockers picrotoxin and bicuculline, and the effect of pentobarbital, these hyperpolarizing responses are shown to be GABAergic Cl-mediated inhibitory postsynaptic potentials (IPSPs).