We prepared 500 µm horizontal brain slices from transgenic mice with fluorescent dopamine (DA) neurons (Zhuang et al, in press). Focal stimulation of the ventral tegmental area (VTA) evoked two kinds of glutamatergic transmission in the nucleus accumbens (nAcc); a monosynaptic early response with about 20 ms latency and a polysynaptic late response with more than 100 ms latency, as we described last year (SFN, 2002). To show that the DA system was intact in the slice, we measured DA release in the nAcc electrochemically. Local stimulation of the nAcc with 3 pulses at 100 Hz evoked 1.2 µM DA release. As we moved the stimulating electrode along the medial forebrain bundle (MFB) toward the VTA, the DA release decreased; focal VTA stimulation generated 30 nM release. These signals were enhanced by nomifensine (DA uptake blocker, 10 µM) confirming that they were due to DA release. In contrast to the early response, the late response appeared to be mediated polysynaptically via cortical inputs. This late respons...