Study Evaluating the Safety, Pharmacokinetics, and Pharmacodynamics of SAM-531

Inclusion criteria * Men aged 20 to 45 years, inclusive, at screening. * Elderly men or women aged 65 years and above as of screening. * Body mass index (BMI) in the range of 17.6 to 26.4 kg/m2 and body weight ≥45 kg. Exclusion critereia * Any significant cardiovascular, hepatic, renal, respiratory, gastrointestinal, endocrine, immunologic, dermatologic, hematologic, neurologic, or psychiatric disease. * Any clinically important deviation from normal limits in physical examination, vital signs, 12-lead ECGs, or clinical laboratory test results. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels should be below the upper limit of normal at screening. * Tobacco use or consumption of any caffeine-containing products (e.g., coffee, tea, chocolate, or carbonated beverages) or alcoholic beverages within 48 hours before study day 1 until the end of the inpatient confinement period.