Peripheral interleukin-6 administration increases extracellular concentrations of serotonin and the evoked release of serotonin in the rat striatum

Previous studies have indicated that peripheral administration of interleuk in-6 (IL-6) increases brain concentrations of tryptophan and 5-hydroxyindol eacetic acid (5-HIAA), the major catabolite of serotonin (5-HT). To determi ne whether these changes were related to increased synaptic release of 5-HT , we studied the responses to peripheral administration of IL-6 by in vivo microdialysis and in vivo amperometry. Intraperitoneal injection of recombi nant IL-6 resulted in an elevation of microdialysate concentrations of 5-HT in the rat striatum. Also, amperometric measurements indicated that i.p. I L-6 enhanced the 5-HT-like signal obtained from the striatum following elec trical stimulation of the dorsal raphe nucleus. These results indicate that the increases in brain concentrations of 5-HIAA observed in earlier studie s indeed reflect increased synaptic release of 5-HT. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.