To identify the effects of activation of striatal ChIs on DA transmission, we incorporated the Autophagy inhibitor light-activated ion channel channelrhodopsin2 (ChR2) into striatal ChIs of mice. ChR2 expression was restricted to ChIs by injecting an adeno-associated virus (AAV) carrying a Cre-inducible ChR2 gene (fused inframe with the coding sequence for enhanced yellow fluorescent protein [eYFP]) into the striatum of transgenic mice expressing Cre-recombinase under the control of the promoter for choline acetyltransferase (ChAT) (Figure 1A)

(also see Supplemental Information available online). In coronal slices that contain DA axons without DA soma, single blue laser flashes (1–2 ms; 473 nm) of ChR2-expressing terminals (15- to 60-μm-diameter spot) in dorsal or ventral NSC 683864 solubility dmso striatum evoked the transient release and reuptake of DA, detected using fast-scan cyclic voltammetry (FCV) at carbon-fiber microelectrodes (see Supplemental Information) (n = 29 animals) (Figure 1B). Extracellular DA concentrations

reached values similar to those evoked by local electrical stimuli (Figure 1B), indicating DA release from a population of axons. Light-evoked DA release was reproducible for several hours (sampling interval ∼2.5 min) and required ACh activation of nAChRs. The β2-nAChR antagonist DHβE abolished DA release (Figure 1C; n = 10, p < 0.001) but not spiking in ChIs (Figure S1E, n = 3) indicating nAChRs postsynaptic to ChIs. ChI-driven DA release did not require muscarinic AChRs (mAChRs, Figure 1D, n = 11), glutamate receptors, or GABA receptors (Figure 1E, n = 9) but was modulated by mechanisms that

normally gate ACh and/or DA exocytosis; it was abolished by Nav+-block by tetrodotoxin (TTX) (n = 10, p < 0.001), zero extracellular Ca2+ (n = 10, p < 0.001), D2 receptor activation with quinpirole, (n = 8, p < 0.001), or mAChR activation with oxotremorine (n = 10, p < 0.001), which limits ACh release from ChIs (Threlfell et al., 2010) (Figure 1E). These observations indicate that endogenous ACh released from ChIs triggers DA SPTLC1 release by activating axonal nAChRs, bypassing action potentials in DA soma. To understand the neuronal events required for ChI-driven DA release, we paired recording of laser-evoked DA using FCV with whole-cell patch-clamp recording of ChR2-expressing, eYFP-tagged ChIs (see Supplemental Information) (Figure 2A). ChR2-expressing ChIs had normal resting membrane potential and TTX-sensitive action potentials (Figure S1; Table S1, n = 11). Laser-evoked DA release was seen after action potentials were evoked in local ChIs (latency 2.0 ± 0.5 ms, Figure 2B, n = 11).