Inclusion Criteria:  All participants will be 18-30 yrs. Healthy non-depressed men and women will have no history or evidence of psychiatric illness and will not have a family history of MDD or major psychiatric illness. Men and women with MDD will have symptomatic depression that meets diagnostic criteria and will be non-medicated. The capacity and willingness to provide written informed consent, to attend all study related visits, and to comply with the study protocol.  Exclusion Criteria:  Subjects will be excluded at the discretion of the PI/collaborating clinician or for any of the following reasons:  psychiatric illness aside from MDD (including current or past psychotic disorders, bipolar disorder, schizophrenia or schizoaffective disorder, panic disorder, post-traumatic stress disorder, obsessive compulsive disorder) subthreshold depression current use of psychotropic medications (including major classes of antidepressants, anxiolytics, antipsychotics, mood stabilizers) active suicidal or homicidal ideation active substance dependence or eating disorders current use of any medications that could alter sympathetic reactivity diagnosed or suspected cardiovascular, renal, or metabolic disease (hypertension, heart disease, diabetes, hyperlipidemia) autonomic disorders tobacco use (including electronic cigarettes) obesity (body mass index > 30 kg/m2) breastfeeding or pregnancy <18 or >30 yrs