We performed ex vivo whole-cell voltage and current-clamp recordings from VTA DA neurons while optically stimulating VTA GABA neurons. Optical stimulation of VTA GABA neurons led to detectable IPSCs in VTA DA neurons that were abolished by bath application of the GABAA receptor antagonist, gabazine (Figure 4A). To examine the effects of optical activation of VTA GABA neurons on the excitability and activity of VTA DA neurons, the membrane potentials of DA neurons were initially set to −60 mV in current clamp. We then applied SCH 900776 concentration 5 s current injection ramps through the patch pipette to evoke firing in the presence and absence of

5 s light pulses to activate VTA GABA neurons. Activation of VTA GABA neurons reduced excitability of VTA

DA neurons as indicated by a significant increase in the rheobase of the recorded neurons compared to recordings when no stimulation occurred (Figures 4B and 4C). In addition, VTA GABA stimulation reduced the activity of VTA DA neurons as indicated by an increase in the interspike interval and a reduction in total number of spikes evoked by the current injection (Figures 4B, 4D, and 4E). Furthermore, to determine whether activation of VTA GABA neurons could functionally suppress GW-572016 datasheet activity-dependent release of NAc DA in vivo, we performed fast-scan cyclic voltammetry experiments in anesthetized mice. Electrical activation of VTA DA neurons resulted in a stimulation frequency-dependent increase in detected NAc DA release, which was significantly attenuated by coincidental 5 s VTA GABA activation

that started 2.5 s before the electrical stimulation of the VTA (Figure 5). Taken together, these data demonstrate that activation of VTA GABA neurons reduces the excitability and evoked activity of neighboring VTA DA neurons in vitro and in vivo. The activity of VTA neurons and subsequent release of DA, glutamate (Stuber et al., 2010, Tecuapetla et al., 2010 and Yamaguchi et al., 2011), and GABA in forebrain targets, such as the NAc, are important processes that promote crucial aspects of motivated because behavior. Thus, the regulation of DA neuronal activity by both intrinsic and extrinsic mechanisms is required for optimal behavioral performance. Further, the mechanisms that regulate DA neuronal activity in adaptive contexts may underlie the maladaptive actions and responses seen in addiction and neuropsychiatric illnesses. In this study, we show that brief activation of VTA GABA neurons selectively disrupts reward consumption when these neurons are stimulated following reward delivery but not when they are activated during reward-predictive cue presentation.