Fig. 1. Electrophysiological and immunohistochemical identification of midbrain dopaminergic neurons in +/+ andwv/wv mice. A, Hyperpolarizing voltage steps from −60 to −120 mV (10 mV increments,Vh of −40 mV) activated the mixed cation current (Ih) in both genotypes. Calibration: 250 msec, 500 pA. B, The corresponding current-clamp recording showed that hyperpolarizing pulses (−0.5 and −1 nA) activated the Ih current, thus producing a typical sag potential in both cells taken form the two genotypes. A depolarizing current pulse (0.5 nA) elicited a pacemaker-like sequence of action potentials in both neurons. Action potential amplitudes are clipped because of low sampling rate of the digital interface. Time bar: 100 msec. C,Left, The white square indicates the mean resting membrane potential (RMP) of +/+ dopaminergic cells (−47.6 ± 1.5 mV, n = 17), and theblack square indicates the mean resting membrane potential of wv/wv cells (−47.1 ± 1.3 mV,n = 18); values were not significantly different (p = 0.81). Right, Thecolumns indicate the mean spontaneous firing recorded in cell-attached configuration in +/+ (white) (2.1 ± 0.12 Hz, n = 7) and wv/wv(black) (2.4 ± 0.2 Hz, n = 15) neurons; values were not significantly different (p = 0.35). D, Confocal laser scanning microscope image of a wv/wv neuron loaded with biocytin (5 mm) through the patch pipette showing typical features of a dopaminergic neuron (magnification, 20×):a, biocytin staining as revealed by FITC fluorescence;b, TH immunostaining as revealed by TRITC fluorescence (note that many neurons, including the recorded one, resulted in being TH-positive, within the SNc); c, merged image of the two fluorescent stainings.