Fig. 8.

Presynaptic GABA_B receptors regulate the amplitude of excitation from thalamocortical onto PGN neurons.A, EPSPs recorded in a PGN cell evoked by local application of glutamate (glu) in lamina A1 (V_m = −75 mV). The local application of baclofen (200 μm in micropipette) results in a 41% reduction in the amplitude of these evoked EPSPs. In contrast, multiple unit activity recorded at the site of glutamate application is unaffected by the application of baclofen in the PGN. The local application of CGP 34348 (2 mm in micropipette) reverses this action of baclofen. B, EPSCs recorded in a PGN cell and induced by glutamate application in A1 lamina (V_holding = −65 mV). In the top traces, four to five superimposed responses of different glutamate applications are shown. The middle traces are the average of the ones above. The simultaneous extracellular recordings of the glutamate activated area of the LGNd are shown in thelowest traces. Local application of baclofen results in a reduction of EPSC amplitude, an effect that is reversed by the local application of CGP 35348. C, Schematic illustration of the recording arrangement used for A andB. All the recordings shown in this figure were performed with 2 m cesium acetate and 25 mm QX 314 in the intracellular electrode to block the activation of outward currents in response to baclofen.