Striatal dopamine (DA) plays a major role in the regulation of motor coordination and in the processing of salient information. We used voltammetry to monitor DA-release evoked by electrical stimulation in striatal slices, where interneurons continuously release acetylcholine. Use of the α6-selective antagonist α-conotoxin MII[E11A] and α4 knockout mice enabled identification of two populations of DA-ergic fibers. The first population had a low action potential threshold, and action potential-evoked DA-release from these fibers was modulated by α6. The second population had a higher action potential threshold, and only α4(non-α6) modulated action potential-evoked DA-release. Striatal DA-ergic neurons fire in both tonic and phasic patterns. When stimuli were applied in a train to mimic phasic firing, more DA-release was observed in α4 knockout versus wild-type mice. Furthermore, block of α4(non-α6), but not of α6, increased DA release evoked by a train. These results indicate that there are different classes of striatal DA-ergic fibers that express different subtypes of nicotinic receptors.