(A) Representative trace of in vivo recorded DA neuron in the VTA. (B) Number of spontaneously active DA neurons recorded per electrode track in VTA (n = 7–8 rats/group). (C) Regional distribution across the VTA of the number of active DA neurons per electrode track (n = 7–8 rats/group). (D) Mean percentage of spikes in bursts and (E) firing rate (Hz) of the recorded DA neurons (n = 29–75 cells/group). Firing rate distribution curves showing (F) the effect of stress and (G) its reversal by PNU282987. Kolmogorov-Smirnov test, control+vehicle vs. CMS+vehicle: p=0.022; CMS+vehicle vs. CMS+PNU282987: p=0.004. (H) Regional distribution across the VTA of average DA neurons firing rate (medial: n = 13–29 cells/group; central: n = 10–28 cells/group; lateral: n = 06–24 cells/group). Firing rate distribution curves showing (I) the effect of stress and (J) its reversal by PNU282987. Kolmogorov-Smirnov test, control+vehicle vs. CMS+vehicle: p=0.092; CMS+vehicle vs. CMS+PNU282987: p=0.066. Data are expressed as mean ± S.E.M. Bonferroni post-hoc test: *p<0.05, **p<0.01, ***p<0.001 comparing with control+vehicle, ##p<0.01, ###p<0.001 comparing with CMS+vehicle.