Opiate receptor avidity in the thalamus is sexually dimorphic in the elderly.

Opiate receptor avidity (B(')(max)/K(D)), was measured in the subcortex of nine females (five healthy subjects, four Alzheimer patients) and 15 males (seven healthy subjects, eight Alzheimer patients), 51-75 years of age, with the opiate receptor antagonist 6-deoxy-6-beta-[(18)F]fluoronaltrexone (cyclofoxy, CF) and a positron emission tomograph. CF avidity was 27.5% less in the thalamus of healthy women compared to healthy men and 48.5% less in Alzheimer disease female patients compared to male patients.