Sex differences in striatal dopamine D2/D3 receptor availability in smokers and non-smokers

In previous research, nicotine-dependent men exhibited lower putamen D-2/D-3 dopamine-receptor availability than non-smokers (Fehr et al. 2008), but parallel assessments were not performed in women. Women and men (19 light smokers, 18 non-smokers) were tested for differences due to sex and smoking in striatal D-2/D-3 dopamine-receptor availability, using positron emission tomography with [F-18]fallypride. Receptor availability was determined using a reference region method, in striatal volumes and in whole-brain, voxel-wise analysis. Significant sex x smoking interactions were observed in the caudate nuclei and putamen. Post-hoc t tests showed that male smokers had significantly lower D-2/D-3 dopamine-receptor availability than female smokers (-17% caudate, -21% putamen) and male non-smokers (-15% caudate, -16% putamen). Female smokers did not differ from non-smokers. Whole-brain analysis demonstrated no statistically significant voxels or clusters. These results suggest that low receptor availability may confer vulnerability to nicotine dependence or that smoking selectively affects D-2/D-3 receptor down-regulation in men but not women.