Neuronal activity and transcription of proinflammatory cytokines, IκBα, and iNOS in the mouse brain during acute endotoxemia and chronic infection with Trypanosoma brucei brucei

Abstract

Trypanosoma brucei brucei (Tbb) infection is a model of chronic immune response associated with severe neurological disorders believed to lead to coma and death. We hypothesized that exaggerated production of proinflammatory molecules within the cental nervous system (CNS) may be involved in the etiology of the disease, i.e., African Tripanosomiasis. The purpose of the present study was therefore to verify the effects of the parasite Tbb on the genetic expression of the immediate-early gene c-fos (index of cellular activity), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), inhibitory factor kappa B alpha (IkappaBalpha, index of the nuclear factor kappaB activity, the transcription factor of numerous proinflammatory molecules), and inducible nitric oxide synthase (iNOS) in the mouse brain. Adult male BALB/c mice received a single intraperitoneal injection of lipopolysaccharide (LPS, used as positive control for these markers that are induced in a transient manner by the endotoxin), Tbb, or vehicle solution and were sacrificed at multiple times (1 hr to 7 days) following the injection. Acute and chronic models induced a robust expression of c-fos in numerous regions of the brain, including the circumventricular organs (CVOs) and different nuclei involved in autonomic control. Although the effect of LPS was rapid and transient, Tbb pathogen stimulated c-fos only within 5 to 7 days. The genes encoding TNF-alpha and IL-6 cytokines were expressed in the CVOs and choroid plexus 1 and 3 hr after LPS injection, whereas no convincing hybridization signal was detected in the brains of Tbb-infected mice at any time. IL-6 and iNOS-expressing cells were also found along large blood vessels of LPS-treated mice, while scattered small TNF-alpha-expressing cells were observed across the brain 12 and 24 hr after the endotoxin treatment. Tbb caused a low to moderate expression of iNOS and IkappaBalpha genes in perivascular cells, but this effect was apparent only several days following the parasite infection. Taken together, these data indicate that LPS and Tbb stimulate c-fos expression in similar nuclei involved in autonomic control, an event occurring within the first 3 hr after the LPS insult and only 5 days post-Tbb injection. The mRNAs encoding proinflammatory cytokines were, however, not detected in Tbb-infected brains, which may be explained by the Tbb variant (MiTat 1.5) that caused high parasitaemias and mortality within 5 to 7 days.