Origin of 5-hydroxyindoleacetic acid in the spinl fluid.

5-Hydroxyindoleacetic acid applied intracisternally in cats does not appear in spinal fluid. Changes of 5-hydroxyindoleacetic acid concentration in the spinal cord are clearly reflected in the perfusate of the spinal subarachnoid space. Thus, 5-hydroxyindoleacetic acid in the spinal fluid originates from the spinal cord and reflects metabolic changes of 5-hydroxytryptamine in the spinal tissue, but not those in the brain.