Interleukin-1 beta increases 5-hydroxyindoleacetic acid release in the hypothalamus in vivo

Push-pull perfusion technique was used to infuse interleukin-1 beta (IL-1 beta) into and collect perfusate from the medial basal hypothalamus (MBH) of conscious, freely moving rats. The serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), was measured in the perfusate by high performance liquid chromatography. Infusion of the vehicle, PBS-0.1% BSA, had no significant effect on 5-HIAA release except near the end of the perfusion period (325 min) when the release was below the pretreatment level (p < 0.05). Infusion of 25 ng of IL-1 beta prevented this decrease, whereas infusion of 50 ng produced an increase of more than 50% (p < 0.05) at 25 min and maintained it at that level during the remaining posttreatment period. In the animals infused with 100 ng of IL-1 beta, 5-HIAA release increased by more than 70% at 25 min and was more than 120% (p < 0.05) above the pretreatment level at the end of the posttreatment period. We concluded that IL-1 beta affects the metabolism of serotonergic system in the hypothalamus and that this is a component of the mechanism by which IL-1 produces its central actions.