The effect of lithium on the increase in forebrain 5-hydroxyindoleacetic acid produced by raphe stimulation

1 The change in forebrain 5-hydroxyindoleacetic acid (5-HIAA) concentration induced by raphe stimulation has been studied in rats treated with Li+ or 0.9% w/v NaCl solution (saline) for 10 days. 2 Raphe stimulation increased the forebrain concentration of 5-HIAA in both groups of animals. Chlorimipramine abolished this effect in the control group, but not in the Li+ group. 3 The inhibition of 5-hydroxytryptamine (5-HT) uptake by chlorimipramine was not affected by pretreatment with Li+ or by the addition of Li+ to synaptosomal suspensions in vitro. 4 It is suggested that the production of 5-HIAA following raphe stimulation in Li+-treated animals is derived from the metabolism of 5-HT which remains within the intracellular environment. The consequence of this in relation to transmitter release is discussed.