(GluEsk) Glutamate and Esketamine

Inclusion Criteria: * Aged 18 to 50 years * Body Mass Index in the range of 18-30 * Sufficiently fluent in English to understand the study instructions * Willing and able to give informed consent for participation in the research Exclusion Criteria: * Currently on any regular prescribed medications (except the contraceptive pill), unless unlikely to compromise safety or affect data quality in the opinion of the Investigator * Known hypersensitivity to the study drug (i.e., esketamine) * History of, or current significant alcohol or substance misuse disorder * Any use of recreational drugs over the last 3 months * Any lifetime use of ketamine or phencyclidine (PCP) * Currently smoking \>/=20 cigarettes/day * History of, or current significant cardiovascular disorder (e.g., hypertension, myocardial infarction) * History of, or current significant neurological disorder (e.g., epilepsy, migraine) or cerebrovascular disorder (e.g., haemorrhagic or ischemic stroke, aneurysmal vascular disease, raised intracranial pressure) * History of, or current significant respiratory, hepatic, urinary tract, or thyroid disorders * History of, or current acute porphyria * History of, or current significant psychiatric disorder (e.g., psychosis, mania, depression) * History of, or current eye disorder, not including refractive error that can be corrected with glasses or contact lenses) * Pregnant, breast feeding, women of child-bearing potential not using appropriate contraceptive measures * Any contraindication to 7T MRI