SEROTONERGIC MEASURES IN BLOOD AND BRAIN AND THEIR CORRELATIONS IN RATS TREATED WITH TRANYLCYPROMINE, A MONOAMINE-OXIDASE INHIBITOR

Tranylcypromine, a monoamine oxidase inhibitor, was administered to ma le Wistar rats in order to investigate its effects on blood and brain serotonin related substances after 1, 4, and 24 h following injection and possible relations between serotonergic measures in central nervou s system and periphery. The dose of the drug tested was responsible fo r an increase in blood serotonin with a simultaneous fall in its metab olite 5-hydroxyindoleacetic acid (5-HIAA) compared to either pretreatm ent or control values. These changes were the most marked after 4 and 24 h following tranylcypromine injection. Almost all brain areas studi ed (cerebellum, medulla, hypothalamus, striatum, midbrain, hippocampus , and cortex) were to be affected by monoamine oxidase inhibitor treat ment. They exhibited a rise in serotonin content starting from 1 h aft er drug administration and lasted in many parts of the brain up to 24 h, which was accompanied by a parallel fall in 5-HIAA level. All these changes were significant when compared to baseline and control values . Alterations in blood serotonin correlated positively with changes in brain serotonin and negatively with brain 5-HIAA, while the opposite pattern of correlations was found regarding blood 5-HIAA and the conte nt of serotonin and 5-HIAA in various brain areas studied. This patter n of correlations speaks in favor of an existence of mutual relations between blood and brain serotonin related substances. Our results sugg est that blood serotonin and-5-HIAA may serve as an index of monoamine oxidase inhibitor action on the central serotonergic system.