Electroconvulsive therapy was originally designed to treat which mental disorder?

Electroconvulsive. Electroconvulsive therapy or ECT was developed for the treatment of chronic and severe depression.
Depression. Ect is used these days most commonly to deal with medication resistant depression, according to one of my psychiatric colleagues, but am also informed of usage for manic-depressive psychosis and schizophrenia, and if one accepts ken kesey's book, "one flew over the cuckoo's nest", for antisocial behaviour control. My colleagues, i'm sure, will provide additional info on this site.