Effect of ARG and IL-1β on hypothalamic 5-HT levels. Serotonin levels, expressed as % of the mean basal level, in 20-min VMH microdialysate samples. Upper Panel: Samples collected before or up to 120 min after the i.c.v. injection of 20 μg of L-arginine (ARG, n = 8) or vehicle (CSF, n = 9). Values are means ±S.E.M. Lower Panel: Samples collected before or up to 180 min after the i.c.v. injection of 10 ng of interleukin-1β, in animals pretreated with 20 μg L-arginine (ARG + IL-1β, n = 8) or not (IL-1β, n = 9). Values are means ±S.E.M. *P <0.05 compared with the respective pre-injection levels. # P <0.05 compared with ARG pre-treatment.