Formula (I), wherein R and R' are hydrocarbon groups, e.g., N,N'-dibutyl-guanidine, N,N'-diphenyl-guanidine, N,N'-di-o-tolyl-guanidine, N-o-tolyl-N'-p-azido-o-tolyl-guanidine and N-adamantyl-N'-o-tolyl-guanidine, are highly selective ligands for sigma brain receptors and are useful in the diagnosis and treatment of hallucination associated psychotic mental illness and chronic mental depression. Tritium labeled N,N'-di-(o-tolyl)-guanidine is useful as a screening tool for compounds having selective sigma receptor binding activity, as it is displaced from isolated mammalian brain membrane to which it is bound portionately to the activity of such a compound.
SIGMA BRAIN RECEPTOR LIGANDS AND THEIR USE