Hypoxia induces selective SAPK/JNK-2-AP-1 pathway activation in the nucleus tractus solitarii of the conscious rat

In the nucleus tractus solitarii, NMDA glutamate receptors are critical to the hypoxic ventilatory response. However, the signal transduction pathways underlying the hypoxic ventilatory response remain undefined. To assess th e effect of a moderate hypoxic stimulus (10% O-2) on tyrosine phosphorylati on of proteins in the nucleus tractus solitarii, tissue lysates were harves ted by repeated punch sampling at 0, 1, 10, and 60 min of hypoxia and exami ned for the presence of phosphorylated tyrosine residues by immunoblotting. Time-dependent phosphotyrosine increases occurred in proteins migrating at regions corresponding to molecular masses of 38-42, 50, 55, and 60 kDa, wh ich were attenuated by pretreatment with the NMDA receptor channel blocker, MK-801. As extracellular signal-regulated kinase (Erk) and stress-activate d protein kinase/c-Jun N-terminal kinase (SAPK/JNK) phosphorylation may ind uce Fos and Jun gene transcription and activator protein-1 (AP-1) DNA bindi ng, the activation of Erk1, Erk2, p38, and SAPK/JNK was examined in the nuc leus tractus solitarii and neocortex during hypoxia and following administr ation of MK-801. Hypoxia enhanced Erk1, Erk2, and p38 activity in the corte x, but not in the nucleus tractus solitarii. Increased phosphorylation of S EK1 and SAPK/JNK-2 occurred in the nucleus tractus solitarii during hypoxia , whereas both SAPK/JNK-1 and SAPK/JNK-2 were recruited in cortex. MK-801 a ttenuated hypoxia-induced SEK1, SAPK/JNK-2, and AP-1 binding in the nucleus tractus solitarii, and the widespread activation of all MAP kinases in the cortex was also attenuated. We conclude that in conscious rats, a moderate hypoxic stimulus elicits NMDA-dependent widespread mitogen-activated prote in kinase activation in cortex, but selective SAPK/JNK-2 and AP-1 activatio n in the nucleus tractus solitarii, thereby suggesting a functional role fo r the SAPK/JNK-2-AP-1 pathway.