Fast oscillation (FO) of an electrooculogram (EOG) was recorded in both eyes of 10 healthy volunteers before and after administration of metoclopramide hydrochloride (MTCL), a D2-selective dopamine receptor antagonist, paying particular attention to sex concerning sensitivity to dopamine in young subjects. Healthy volunteers were divided into male and female groups; 5 males (10 eyes) aged 21 to 23 years (average, 21.8 years) and 5 females (10 eyes) aged 19 to 25 years (average, 21.8 years). As an FO parameter, the dfFO (the averaged difference in ?V between maximum amplitude in the dark period and minimum amplitude in the light period during FO measurement) was evaluated. The mean level of dfFO significantly increased between phase A (the initial 10 min before intravenous injection of 10 mg of MTCL) and phase B (10 min after the injection) in the male and female groups (P < 0.01 and P < 0.025) and between phase A and phase C (the additional 10 min after the injection) in both groups (P < 0.01 and P < 0.05). The mean level of dfFO in the female group was significantly higher than that of the male group in phase B (P < 0.05). As a control, the experimental procedure was performed with physiological saline administration, and no changes were observed. The data suggest that there exists some difference between young males and females generation concerning sensitivity to dopamine and that young females may show a higher-than-male sensitivity to dopamine in the occurrence of FO potential
