Quadratic regression analysis revealed significant inverted U-shaped relations between D1 receptors in PFC and WCST performance. That is, a too high or too low level of D1 receptor expression in PFC leads to high errors and a low number of categories achieved. (J Neurosci 2008 abstract)

Smokers showed a significant decrease in the binding potetial of dopamine D2 receptor in the ventral striatum following nicotine administration, but nonsmokers did not show such a decrease. The reduction of binding potential was correlated with the degree of nicotine dependence measured by Fagerstrom Test for Nicotine Dependence. This might reflect enhanced dopamine release in smokers and the reinforced effect of nicotine. (Int J Neuropsychopharmacol 2008 abstract)