Neural Responses and Dysphoria: Modulation by a Pharmacological Probe

Inclusion Criteria: * Male or female aged 18 to 45 years, inclusive at Randomisation visit. * Fluent English speakers. * Beck Depression Inventory (BDI) score of 05 or ≥10 at both Screening and Randomisation visits. * Hamilton Depression Rating Scale (HAMD)score of \<24 at both Screening and Randomisation visits. * Healthy at Screening visit as determined by a physician. * Female participants should be surgically sterile or abstinent or, if sexually active, be practising an effective method of birth control. * Acceptable weight as defined by body mass index (BMI) range of 18 to 30 kg/m², inclusive. * Normotensive with sitting (5 minutes) blood pressure between the range of 100 to 140 mmHg systolic, inclusive and 60 to 90 mmHg diastolic, inclusive at Screening. * Non smoker or light smoker (≤ 5 cigarettes per day). * Participants must have signed the Informed Consent Form. * Participants providing a genetic sample must have signed the DNA consent. Exclusion Criteria: * History of alcohol or substance dependence within the last 6 months. * Consumption of large amounts of caffeinated drinks. * Relevant history or presence upon clinical examination, of cardiac, ophthalmologic, pulmonary, endocrine (diabetes),cancer, blood disease, gastrointestinal, hepatic or renal disease or other condition. * History or presence of significant neurological or psychiatric conditions. Exceptions to this are participants with a history of depression for the dysphoric group. Participants with generalised anxiety disorder or other anxiety disorders may be entered at the discretion of the Investigator. * Participants who, in the opinion of the Investigator, are at risk of suicide. * Any use of sedative hypnotics, including benzodiazepines, zolpidem or zopiclone within the last 3 months prior to Randomisation visit. * Any use of medications for depression in the last three months prior to Randomisation visit. * Have received prescribed medication within 14 days prior to Randomisation visit (apart from the contraceptive pill). * Have received over-the-counter (OTC) medicine within 48 hours prior to Randomisation visit. * Have received an experimental drug and/or used an experimental medical device within 30 days of Randomisation visit or within a period less than 5 times the drug's half life, whichever is longer. * If female: are pregnant or are trying to get pregnant or are currently breast feeding. * History of, or current condition of, migraine headaches or have undergone operations to the head. * Significant hearing impairment. * Significant visual impairment or history of ocular treatment. * Lefthanded. * Previous experience of the emotional test battery experimental procedures. * Unable to comply with magnetic resonance (MR) Patient Declaration. * Involvement in an emergency (medically emergent) situation between Screening and Randomisation visits. * Surgery between Screening and Randomisation visits. * Unable or unwilling to comply with study procedures.