Lipopolysaccharide (LPS)-Induced Fos Expression in the Brains of Febrile Rats

We have mapped the distribution of Fos-like immunoreactivity (FLI) in the brains of restraint-trained, LPS-treated rats. Fos was visualized in the septum, preoptic area, endocrine hypothalamus, bed nuclei of the stria terminalis, thalamus, amygdala, and nuclei of the solitary tract. Only diffusely scattered FLI neurons were observed in these regions of trained pyrogen-free saline (PFS)-treated controls. But FLI neurons were abundant in these regions of untrained PFS-treated rats, and also in other regions thought to be involved in stress. Thus, discrete hypothalamic and brainstem nuclei are activated by LPS and overlap to some extent with those stimulated by stress.