Characterize the Regional Distribution of [11C] ABP688 in Brain by Positron Emission Tomography (PET)

Inclusion Criteria: * Male and female subjects 55-80 (inclusive) * Subjects in good health At screening: * oral body temperature between 35-37.5C * systolic blood pressure: 90-140 mm Hg * diastolic blood pressure: 50-90 mm Hg * pulse rate: 40-90 bpm * Female subjects of child bearing potential must have been using a double-barrier local contraception * Postmenopausal women must have had no menstrual bleeding * Subjects must have weighed at least 50 kg * All subjects must provide informed consent * All subjects must have been able to communicate well with investigator Specific to Major depression disorder (MDD) Patients had to show following level of symptomatology: * HAM-D (17-item scale) \> 16 * CGI \> 4 (moderately ill) Exclusion Criteria: Specific criteria for healthy volunteers: \- Presence and/or history of clinically significant major neurological or psychiatric disorder Specific criteria for MDD patients: * Presence and/or history of a clinically significant major neurological or psychiatric disorder other than MDD or generalized anxiety disorder * Axis I co-morbidity was excluded except anxiety spectrum disorders Criteria for both: * Smokers * Pregnancy * Subjects with history of or symptoms/complaints consistent with mild cognitive impairment * Use of any psychotropic prescription drugs * Coffee consumers more than 6 cups/day * Participation in any clinical investigation * Donation or loss of 400 mL or more of blood * Significant illness within 2 weeks prior to dosing * A known hypersensitivity to study drug * MRI scan that showed evidence of stroke * Any surgical or medical condition which might have significantly altered distribution * Clinical evidence of any abnormal lab value * History of immunodeficiency disease * Positive Hepatitis B surface antigen * Presence of contraindications to PET scan investigations- Presence of contraindications to MRI investigations * Evidence from an Allen test of incomplete communication * History of drug or alcohol abuse * Current use of anticonvulsant * Significant radiation exposure Other protocol-defined inclusion/exclusion criteria may apply.