Fig. 4

Systemic LPS blocks hypoxia-induced phosphorylation of ERK1/2 MAPK. a Double immunofluorescence staining of phosphorylated ERK1/2 MAPK (dark brown puncta) with the retrograde tracer (green) Cholera toxin B fragment (CtB) in phrenic motor neurons in the ventral horn of the cervical spinal cord. Representative × 20 magnification of the C4 segment of the spinal cord reveals minimal staining for phospho ERK1/2 MAPK on/near phrenic motor neurons in a vehicle treated rat that was not exposed to hypoxia. In contrast, phospho ERK1/2 MAPK staining appeared more intense in response to moderate acute intermittent hypoxia (mAIH) relative to normoxic controls. When pre-treated with LPS however, mAIH no longer appeared to increase ERK1/2 MAPK phosphorylation levels. b Average group data demonstrating that mAIH causes a significant enhancement in phosphorylated ERK1/2 MAPK levels on/near phrenic motor neurons. In contrast, mAIH failed to enhance phosphorylated ERK1/2 MAPK levels in rats pre-treated with LPS. Data are means ± S.E. *Significant difference from vehicle treated normoxia group and # indicates significant difference compared to all other groups: for all, p < 0.05. A.U., arbitrary units