Fig. 2.

Effects of p-tyr and EPPTB on the spontaneous firing rate of DA neurons in the VTA. (A) In neurons of WT mice, the firing frequency was assessed before (control) and during the application of p-tyr alone and in combination with EPPTB. EPPTB not only inhibited the p-tyr-mediated decrease in firing frequency but increased the firing frequency over control levels (control, 2.1 ± 0.8 Hz; p-tyr, 0.5 ± 0.1 Hz; p-tyr + EPPTB, 15.1 ± 1.0 Hz; n = 10; ***, P < 0.001 for p-tyr + EPPTB versus p-tyr). (B) In neurons of Taar1^−/− mice the firing frequency was not significantly affected by application of p-tyr or EPPTB (control, 16.0 ± 1.0 Hz; p-tyr, 15.0 ± 1.3 Hz; p-tyr + EPPTB, 16.1 ± 1.1 Hz; n = 10). (C) In neurons of WT mice the firing frequency was significantly increased by EPPTB in the absence of p-tyr application. After wash-out of EPPTB for 1 h (wash) the firing frequency reverted close to control levels (control, 1.9 ± 0.2 Hz; EPPTB, 15.1 ± 1.0 Hz; wash, 3.5 ± 0.8 Hz; n = 4; ***, P < 0.001 for EPPTB versus control). (D) In neurons of Taar1^−/− mice, EPPTB had no effect on the firing frequency (control, 14.3 ± 1.1 Hz; EPPTB, 14.8 ± 0.9 Hz; wash, 15.2 ± 0.9 Hz; n = 6). In A–D, representative recordings are shown on the left and summary bar graphs on the right. (Scale bar, 20 mV/2 s.)