The purpose of this study is to test the effects of the medication ketamine and the
medication called nitroprusside in patients with major depression. Ketamine has both good and
bad effects. Some studies have shown that ketamine improves depression. However, studies have
also shown that it causes strange and sometimes unpleasant sensations referred to "psychotic"
or "dissociative" symptoms. An example of a psychotic symptom would be hearing or seeing
something that in reality is not there. The study team would like to see if nitroprusside can
prevent the reported bad effects of ketamine without blocking the reported good effects. This
might make ketamine a better treatment for depression.