Is Brain Insulin Resistance a Feature of the Biology of Depression in Adolescents

Inclusion Criteria: * Age 14- 18 * One of the following: Diagnosis of Major Depressive Disorder (MDD) or Persistent Depressive Disorder (PDD); or score ≥22 on the Mood and Feeling Questionnaire and confirmation of depression with the Mini International Neuropsychiatric Interview Kid (MINI Kid) * BMI between 5-95th population percentile and Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) ≤2.5 calculated using fasting blood work values (glucose and insulin) Exclusion Criteria: * History of primary psychotic illness * Use of antipsychotics or mood stabilizers * History of current substance use disorder (moderate to severe) * Pre-diabetes or diabetes (fasting glucose ≥6.0 mmol/l or use of anti-diabetic drug) * Evidence of impaired glucose tolerance on screening oral glucose tolerance test (OGTT) * Use of weight, lipids, or blood pressure reducing agents * History of liver disease or AST\>2 times upper limit of normal * History of kidney disease * MRI contraindications * Positive pregnancy test * Allergic to exogenous insulin * Positive result on urine drug screen (participants with positive cannabis and alcohol urine drug screens may still be eligible for the study; positive drug screens for other substances will be exclusionary)