Figure 3.
The GABAB receptor agonist baclofen depresses the amplitude of evoked EPSCs and increases the PPR in laminae III/IV neurons. (a) Effect of 1 and 2.5 µM baclofen on EPSCs evoked by Aβ fiber stimulation and recorded from a laminae III/IV neuron held at −70 mV. The EPSCs were recorded applying the paired-pulse protocol (100 ms interval). At each stimulus, baclofen depresses the early, monosynaptic EPSC and completely suppresses the slower, polysynaptic response. (b) Time course of baclofen effect in the same neuron. (c) PPR determined from the EPSCs shown in (a), in the different experimental conditions. Both baclofen concentrations increase PPR, suggesting a presynaptic effect. (d) Intracellular perfusion of the G protein blocker GDP-β-S does not prevent the depressing effect of 1 µM baclofen on evoked EPSCs, recorded from a different laminae III/IV neuron. (e) Dose-dependent effect of baclofen on peak amplitudes of evoked EPSCs, recorded with the paired-pulse protocol from a total of 45 laminae III/IV neurons. (f) PPR values obtained from the same EPSCs analyzed in (e), determined in control and in the presence of different concentrations of baclofen. A significant increase of PPR was observed at each baclofen concentration (paired t-test, p < 0.05 or p < 0.01).