°C in the same physiological saline perfused at 2–3 ml/min. Neurons were visualized using a 40x objective on an upright microscope (BX51WI; Olympus America, Center Valley, PA) with infrared/oblique illumination optics. Loose-patch recordings (~10–20 M Ω seal) of dopamine neuron firing were made in a voltage clamp using borosilicate glass pipettes (2.2–2.5 M Ω) filled with 150 mM NaCl. Putative dopamine neurons were identified by spontaneous pacemaker firing (0.5–5 Hz) and broad action potentials (>1.2 ms) (Ford et al., 2006). A Multi-clamp 700-A amplifier (Molecular Devices, Union City, CA) was used to record the data, which were filtered at 5 kHz, digitized at 10 kHz, and collected using AxoGraph X (AxoGraph Scientific, Sydney, Australia).
