Stimulation of dopamine D1 receptors suppresses whole-cell Na⁺ currents in NAc neurons. Current traces (inset) and time course showing that the D1 receptor selective agonist SKF 38393 (1 μm) reversibly suppressed whole-cell Na⁺ current in an untreated NAc neuron. The effect was observed in 33/40 neurons tested (mean ± SEM = 24.5 ± 2.1% suppression; see Fig. 8 for concentration–effect curves). The dopamine D1 receptor-selective antagonist SCH 23390 (1 μm) completely prevented the suppression of current by SKF 38393 (n = 6). Currents were evoked by stepping the membrane from the holding potential of −70 mV to the test potential of −20 mV (seeprotocol above traces) where Na⁺current was near-maximal (I–V tests not shown). Na⁺ currents were completely prevented by tetrodotoxin (1–2 μm; not shown), exhibited a reversal potential of ∼50 mV, and inactivated rapidly. Thenumber associated with each trace indicates the point during the time course at which the trace was obtained.