Effect of folic acid and vitamin B12 deficiencies on 5-hydroxyindoleacetic acid in human cerebrospinal fluid.

Indoles were measured in cerebrospinal fluid (CSF) from control patients, from patients suffering from folate deficiency, and from patients with vitamin B12 deficiency. The folate-deficient patients were classified according to whether they exhibited a neuropsychiatric syndrome, consisting of organic mental changes, polyneuropathy, and depression, which responded to folate administration. CSF 5-hydroxyindoleacetic acid was low in the vitamin B12-deficient patients and in those folate-deficient patients whose symptoms were not related to folate deficiency. CSF 5-hydroxyindoleacetic acid returned to normal with folate treatment in the patients exhibiting folate-responsive neuropsychiatric signs. The data indicate a close association between folate-responsive neuropsychiatric symptoms and changes in 5-hydroxytryptamine metabolism in the central nervous system.