Serotonin concentrations in normal aging human brains: Relation to serotonin receptors

Concentrations of serotonin (5-HT) and its deaminated metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured in 7 regions of normal human brains and, in some of the regions, were compared to the number of serotonin receptors (S1 and S2). Neither 5-HT nor 5-HIAA concentrations correlated significantly with increasing age (from 17–100 years) in any of the regions investigated. Positive correlations between 5-HT and 5-HIAA were found in all regions studied, significantly (p<0.05) so in 5 of the areas. When comparing 5-HT transmitter and metabolite concentrations to the number of S1 and S2 receptors, no significant correlations were found either within any brain area of between different brain regions. These data confirm that 5-HT transmitter concentrations are not altered by increasing age, support the ideas that S1 and S2 receptors are not presynaptic and also that 5-HT transmitter concentrations and receptor densities are separately controlled.