The laboratory study, which was conducted independently from the GWAS, included 179 non-treatment-seeking EA (50%) and AA (50%) smokers recruited from the New Haven, Connecticut area. Seventy-three percent of subjects were male and the mean age was 36.2 (s.d.=8.9) years. Some subjects from this sample have been included in previous studies, including genetic studies related to smoking and nicotine.31–34 All laboratory subjects smoked > 10 cigarettes/day for the past year and had expired carbon monoxide levels of ≥10 ppm at the initial screening. Based on a structured interview (Structured Clinical Interview for DSM-IV),35 the subjects were free of major medical problems and current psychiatric disorders, including dependence on alcohol or drugs (other than nicotine). Plasma nicotine, cotinine, and 3′-hydroxycotinine concentrations were measured at baseline (prior to nicotine infusion) using HPLC interfaced with tandem mass spectrometry (LC/MS/MS), as previously described.31, 36 Baseline Minnesota Nicotine Withdrawal Scale (MNWS)37 and Brief Questionnaire of Smoking Urges (BQSU) 38 were completed after IV lines were established. After baseline assessments, subjects were administered IV doses of saline, followed in uniform order by escalating doses of nicotine
