Temporal and spatial relationships between lipopolysaccharide-induced expression of Fos, interleukin-1β and inducible nitric oxide synthase in rat brain

Interleukin-1β plays an important role in mediating central components of the host response to peripheral infection such as fever and neuroendocrine activation by acting in the brain. The present study assessed whether interleukin-1β produced in the brain is relevant to neuronal activation and the fever response induced by intraperitoneal injection of bacterial lipopolysaccharide. The distributions of Fos protein, interleukin-1β protein and inducible nitric oxide synthase messenger RNA, used as an anatomical indicator of interleukin-1β bioactivity, were compared in brains of animals killed 2, 4 or 8 h after lipopolysaccharide (250 μg/kg) or saline injection. Saline did not induce interleukin-1β or Fos immunoreactivity in the brain. Interleukin-1β positive cells were found 2 h after lipopolysaccharide injection in circumventricular organs. Fos immunoreactivity at this time- point was not found in circumventricular organs, but in parenchymal structures such as the nucleus of the solitary tract, paraventricular hypothalamus and ventromedial preoptic area. Fos expression did occur in circumventricular organs only 8 h after lipopolysaccharide injection. This late pattern of Fos expression coincided with the rise in body temperature and the induction of inducible nitric oxide synthase messenger RNA. These data show that after peripheral lipopolysaccharide administration interleukin-1β is synthesized and bioactive in circumventricular organs. Interleukin-1β may activate local neurons that induce fever and neuroendocrine activation via projections to the ventromedial preoptic area and the nucleus of the solitary tract.