Effect of tryptophan administration on 5HIAA in cerebrospinal fluid in man.

Abstract

Because of the relative inaccessibility of the brain, attempts to quantify in man the rate of cerebral metabolism of any particular compound are fraught with difficulties. Measurements of urinary end products of brain metabolism are often invalidated by the presence of the same metabolites which originate in other tissues. Cerebral arteriovenous differences in the concentration of metabolites may be technically difficult to estimate and rely on the demonstration of a concentration gradient across the brain to evaluate the rate of production. The concentration of metabolites in the cerebrospinal fluid (CSF) may, however, provide an index of the turnover of substances in the brain. 5-Hydroxytryptamine (5HT) is found in high concentration in central structures of brain of animals and man (Garattini and Valzelli, 1965). It appears to be localized in fine neurones whose cell bodies arise in the mid-brain raphe nuclei and ramify both upwards to other structures, including the cortex, and downwards to the spinal cord (Anden, Dahlstrom, Fuxe, Larsson, Olson, and Ungerstedt, 1966). The function of these 5-hydroxytryptamin-ergic neurones is not known, but the system has been implicated in the control of sleep (Koella and