Whole-cell recordings were performed in acute coronal slices from TH-Cre mice co-injected with DIO-EYFP and DIO-ChR2(E123T/T159C)-mCherry viral vectors. Cells were identified based on EYFP expression and recorded in current-clamp mode. Cells were then classified as ChR2+ or ChR2− based on the presence or absence of a direct, short-latency (<1 ms) light-evoked photocurrent response. a, Differential interference contrast (top) and mCherry fluorescence (bottom) images of a TH+ AVPV cell expressing ChR2–mCherry. Scale bar, 20 µm. b, Light-evoked spiking fidelity in TH+ AVPV neurons across varying light pulse frequencies (ChR2+, n = 12 cells; ChR2−, n = 10 cells). Light pulse trains containing 20 pulses (10 ms, 19 mW mm−2, 475 nm) at each frequency were used to calculate response rates. Only spikes that occurred within 10 ms of light onset were calculated as direct responses. Apparent responses in ChR2− cells are attributed to the ongoing spontaneous firing of these neurons. c, Current clamp recording of voltage responses to negative (100 pA, red) and positive (50 pA, black) current injections in an AVPV TH+ neuron. d–i, Intrinsic electrical properties of TH+/ChR2+ (blue bars) and TH+/ChR2− (white bars) cells, calculated from responses to current injections as shown in c: input resistance (d), spontaneous action potential firing rate (e), width of action potentials at half-maximum (f), resting membrane potential (g), action potential threshold (h) and membrane time constant (i). All showed no marked difference between ChR2+ and ChR2− cells (ChR2+, n = 8; ChR2−, n = 4). j, Action potential firing rates of TH+/ChR2+ cells recorded in whole-cell patch clamp mode before, during and after 1 Hz optogenetic stimulation (data are means ± s.e.m., ***P < 0.05, paired t-test, n = 7 cells).