(A) The experimental configuration. Representative traces showing the control NMDAR-mediated synaptic current and the currents evoked after application of the labeled doses of AMT. (B) Dose-response relationship of the AMT modulation of NMDAR-mediated current in dSPNs and iSPNs. IC₅₀ = 641 μM (iSPN n = 5–10); IC₅₀ = 648 μM (dSPN n = 5–11). (C) Current-voltage relationship at negative membrane potentials revealed an inwardly rectifying current. Cells were held at –60 mV and stepped up to –130 mV in –10-mV increments in the presence of tetrodotoxin (1 μM). Subsequent bath application of Ba²⁺ (200 μM) blocked all Kir2 channel currents, leaving currents attributable to KCNK channels. Subtraction of the records before and after Ba²⁺ application showed a Ba²⁺-sensitive Kir2 current. (D) The Ba²⁺-subtracted current plotted against the step potential. The data points were fit with a Boltzmann equation. (E) The Kir2 current evoked by a voltage steps from –60 mV to –130 mV was reduced by a range of AMT concentrations (10, 50, or 100 μM). (F) Dose-response relationship of the AMT suppression of Kir2 current. IC₅₀ = 29 μM (n = 4–6). (G) Box plot showing the effect of AMT on IC₅₀s between iSPNs and dSPNs (iSPN n = 5, dSPN n = 4, P > 0.05 by Mann-Whitney test). NS, not significant. (H) Average Ba²⁺-sensitive currents recorded at –120 mV from CHO-K1 cells stably expressing Kir2.1 and exposed to vehicle, 3, 10, 100, 500, or 3000 μM AMT. (I) Dose-response curve of Kir2.1 current measured after exposure to various AMT concentrations (n = 12–23) and IC₅₀ = 38.3 ± 3.1 μM. Data are shown as mean ± SEM.