Fig. 5.

DAT inhibitors block the dopamine neuron excitation produced by DAT substrates. Pacemaker firing of dopamine neurons was recorded in the presence of dopamine receptor antagonists (200–500 nM sulpiride, 500 nM SKF 83566, and 100 nM prazosin). Bath perfusion of methamphetamine (10 μM) increased firing rate, an effect that was quickly reversed by the nonselective DAT inhibitor cocaine (A; n = 5 cells from 2 mice). The methamphetamine-induced increase in firing was blocked by preincubation with either the norepinephrine/dopamine transporter inhibitor nomifensine (1–3 μM) or the selective DAT inhibitor GBR 12909 (1 μM), but not by the serotonin transporter inhibitor fluoxetine (800 nM; B). Summarized data are illustrated in C (1-way ANOVA followed by Dunnett's post hoc test: ***P < 0.001). In the presence of the D2 receptor antagonist eticlopride (100 nM), bath perfusion of the endogenous DAT substrate dopamine (100 μM) also increased dopamine neuron firing rate, an effect that was also rapidly reversed by cocaine (D; n = 6 cells from 3 mice). To investigate the voltage dependence of the DAT-mediated excitation, we obtained whole cell voltage-clamp recordings using the gramicidin perforated-patch technique in the presence of pharmacological blockers of dopamine receptors (sulpiride, SKF 83566, and prazosin). Under these conditions, bath perfusion of methamphetamine (10 μM) consistently produced a small inward current that was reversed by the DAT inhibitor cocaine (E). Methamphetamine produced inward currents at holding voltages ranging from −40 to −95 mV, suggesting that DAT-mediated excitation is not voltage dependent at subthreshold voltages (F). Each data point represents an individual perforated-patch experiment performed at the indicated holding voltage.