Age dependence of the effects of activating GABA_A and GABA_B receptors. Each experiment shows membrane potential responses to application of GABA (50 μm), to activation of GABA_B receptors by baclofen (50 μm), and to the activation of GABA_A receptors by muscimol (50 μm).A, B, In animals older than P7, activation of GABA_A receptors induced a depolarizing response, whereas GABA_B receptor activation induced a hyperpolarization. The effects of GABA were a balance depending on combined responses of both receptor subtypes. C, In interneurons from young (P1–P4) animals, GABA_B receptor activation had no effect, and both GABA and muscimol induced depolarizing responses.