Figure 6. Distinct kinetics of D2ICs versus GABA_B IPSCs in SNc DA neurons and lack of effect of LC/A on evoked GABA_B IPSCs.

(A) Evoked D2ICs and GABA_B IPSCs recorded in separate DA neurons. Sulpiride (1 μM) abolished evoked D2ICs (A₁) and CGP55845 (300 nM), a GABA_B receptor antagonist, abolished GABA_B IPSCs (A₂).

(B) Kinetics of D2ICs and GABA_B IPSCs. Comparison of peak amplitude (B₁), time to peak (B₂), decay time (B₃), and area under the curve (AUC) (B₄) for D2ICs (n = 8) and GABA_B IPSCs (n = 7). Peak amplitude (D2IC, 28.3 ± 3.8 pA; GABA_B IPSC, 22.3 ± 3.5 pA, p = 0.3), time to peak (D2ICs, 283 ± 16 ms; GABA_B IPSCs, 66 ± 7 ms, ***p < 0.001), decay time constant (D2ICs, 436 ± 27 ms; GABA_B IPSCs, 163 ± 9 ms, ***p < 0.001), AUC (pA*ms) (D2ICs, 15.4 ± 2.2 × 10³; GABA_B IPSC, 3.9 ± 0.7 × 10³, ***p < 0.001). Bars are means ± SEM; unpaired t test.

(C) Time course of evoked GABA_B IPSC amplitude, normalized to initial for each DA neuron with vehicle or LC/A in the pipette (vehicle, n = 6; LC/A, n = 7).

(D) Representative evoked GABA_B IPSC recorded in voltage-clamp mode after establishing whole-cell recording (initial) and at the end of recording (final).

(E) Final GABA_B IPSCs recorded with vehicle or LC/A (vehicle, 88% ± 9% of initial, n = 6, p = 0.12; LC/A, 86% ± 16%, n = 7, p = 0.5; paired t test).