Sex Differences in the Striatal Dopamine D₂ Receptor Binding Characteristics in Vivo

OBJECTIVE: The authors investigated whether striatal dopamine D₂ receptor binding characteristics in vivo are similar in men and women and whether there are sex-related differences in the decline in D₂ receptor density due to aging. METHOD: Striatal D₂ receptor density (B_max), affinity (K_d), and binding potential (B_max/K_d) were measured with positron emission tomography and [¹¹C]raclopride in 54 healthy subjects (33 men and 21 women). RESULTS: Women had generally lower D₂ receptor affinity than men, and this difference was statistically significant in the left striatum. B_max and B_max/K_d tended to decline with age twice as fast in men as in women, but the difference did not reach statistical significance. CONCLUSIONS: These results confirm the age-related reduction of D₂ receptor density and binding potential in both sexes in vivo. The lower D₂ receptor affinity suggests an increased endogenous striatal dopamine concentration in women. This may have implications for the differential vulnerability of men and women to psychiatric disorders like schizophrenia and alcohol and substance dependence.