Fig. 1

Endogenous, activity dependent activation of presynaptic GABA_A receptors. a Averaged evoked EPSCs (from 5 to 6 traces), obtained by repetitively stimulating the primary afferent fibers (four pulses, 10 Hz), while recording from a lamina III/IV neuron. In this example, the second eEPSC peak (marked by the arrow) is smaller than the first, third and fourth peaks. The GABA_A receptor antagonist, gabazine, caused a substantial increase of the second peak that is reversible in wash. b Time course of the effect of gabazine on the first (circles) and second peak (triangles), from the example shown in a. Parallel vertical bars indicate the time course during which gabazine was added to the bath. c Mean amplitude values of the four eEPSC peaks from the same recording as shown in a, determined under the different experimental conditions. d Evoked EPSCs recorded from a different lamina III/IV neuron (averaged EPSCs from five consecutive traces). Under control conditions, the eEPSC peaks show a different pattern of amplitude changes compared to the neuron in a, with the second peak being larger than the third and fourth. In this case the second peak amplitude is not altered by gabazine. e Mean peak amplitudes are plotted from the same data as shown in d