The ubiquitous serotonin is found in such diverse substances as the venom of wasps and scorpions; the salivary glands of the octopus; and the intestinal mucosa, blood platelets, and brain of various mammals. During clotting it appears free in serum. It is believed that this "free" serotonin causes contraction or spasm of the smaller blood vessels which assists in controlling hemorrhage. Its presence in the brain, particularly in the hypothalamus and midbrain, and the fact that many of its structural analogs (ie, lysergic acid diethylamide) produce hallucinations and other symptoms of psychosis, led to the suggestion by Woolley and Shaw,1 in 1954, that serotonin may have a causal relationship to mental disease.
Employing a new technique for quantitating aggregation of blood cells (screen filtration pressure method), Swank et al2 recently found that the addition of less than 1.0μg of serotonin per milliliter to blood in vitro caused marked