Figure 1. Optogenetic Stimulation and Recording of VTA Dopamine Neurons.

(A) Expression of ChR2-eYFP (top) and TH (bottom) in VTA of a representative Th::Cre rat. Scale bar, 550 μm. White triangles point to optical fiber termination just dorsal to VTA.

(B) (Top) Schematic of an optrode implantation in VTA. (Bottom) Simultaneous optogenetic stimulation and recording in VTA in freely moving Th::Cre rats.

(C) Stimulation protocols.

(D) Example phasic responses of VTA dopamine neurons to behavioral events (left) and the corresponding neuron’s waveform (right). (Top) Sustained phasic response prior to cue onset (t = 0 s, bin size = 1 s) during an attention task, adapted from (Totah et al., 2013). (Bottom) Transient burst during reward delivery (t = 0 s, bin size = 0.1 s) in a Pavlovian conditioning task, adapted from (Wegener, 2017).

(E) Responses of three well-isolated VTA units (from n = 2 Th::Cre rats) to different stimulation protocols are presented in separate rows as rasters (top) and perievent histograms (bottom; bin size = 1 s [sustained phasic], bin size = 0.1 s [fast and slow burst]). Trial numbers are shown on rasters. Blue rectangles mark the period of stimulation.

(F) Probability of unit spiking at latencies 0–10 ms from the delivery of single blue laser pulses. Each graph corresponds to the unit presented in the same row in (E).

(G) Raw voltage traces for unit 2 showing responses to sustained phasic (top), fast burst (middle), and slow burst (bottom) stimulation. Blue squares indicate when each laser pulse was delivered.

See Figure S1.