368. Muscarinic 2 receptors in cognitively normal young and old volunteers

metabolite homovanillic acid in cerebrospinal fluid. We assessed the striatal presynaptic dopamine function using anatomical MRI and positron emission tomography (HR1 tomograph) with [ 18 F]fluorodopa in right-handed depressed patients selected for psychomotor retardation (n 5 6) as compared with depressed patients selected for high impulsiveness (n 5 6), and healthy subjects (n 5 10). Depressed patients were matched for severity of depression on the MADRS Depression Rating Scale, with scores ranging from 25 to 37. The Depressive Retardation Rating Scale score was higher in retarded depressives than in impulsive depressives (mean 6 SD: 22 6 3v s 126 4; p 5 0.006). Impulsivity was defined as scoring .10 on the “loss of control” subscale of the Depressive Mood Scale, and .10 on the Tyrer anxiety scale. Loss of control score was lower in patients with retardation than in impulsive patients (6 6 4v s 146 3; p 5 0.004); anxiety mean score was lower in patients with retardation than in impulsive patients (14 6 5v s 206 3; p 5 0.02). While the mean caudate and putamen [ 18 F]fluorodopa uptake constant Ki values were similar in patients and controls, the left caudate Ki value in patients with marked psychomotor retardation (113 6 8 3 10 24 ) was significantly lower (p 5 0.005) than that in controls (127 6 7 3 10 24 ), and in patients without retardation (146 6 7 3 10 24 ). Impulsive patients did not differ from controls. Thus, a decreased presynaptic dopamine function was found in the left caudate of retarded depressed patients only, providing direct evidence of a link between hypodopaminergia and depressive psychomotor retardation.