Chronic nicotine increases expression of α4* nAChRs on GABAergic somata of the ventral tegmental area (VTA). A-C) Low magnification images showing α4YFP expression (green) in dopaminergic neurons (TH, magenta) in the VTA. D-F) Higher power images showing immunohistochemical labeling of α4YFP (green) (D) on GABAergic (GAD67, red) (E) and dopaminergic (TH, magenta) (F) neurons of the VTA. G) Merged image showing α4YFP expression on a TH positive and a GAD67 positive neurons. H) Chronic nicotine causes an upregulation (57 ± 10%) of α4YFP* nAChRs on GABAergic somata of the VTA (p = 0.005, two sample t-test) as compared to saline controls, but α4YFP expression in dopaminergic neurons are unaffected (−8 ± 8%) (p = 0.5, Wilcoxon rank sum test). All n values are the total number of neurons imaged and analyzed from 5 nicotine pump mice and 5 saline pump mice.