||As the origin of a “life-and-death” signal that reflects central cardiovascular regulatory failure during brain stem death, the rostral ventrolateral medulla (RVLM) is a suitable neural substrate to evaluate the cellular mechanism of this fateful phenomenon. Based on a clinically relevant animal model that employed the organophosphate pesticide mevinphos (Mev) as the experimental insult, this study evaluated two hypotheses. First, transcriptional upregulation of nitric oxide synthase I or II (NOS I or II) gene expression by nuclear factor-κB (NF-κB) on activation of phosphoinositide 3-kinases (PI3K)/Akt/phosphatase and tensin homologue deleted on chromosome ten (PTEN) cascade in the RVLM underlies brain stem death. Second, muscarinic receptor-independent activation of cyclic adenosine monophosphate-dependent protein kinase A (PKA) in the RVLM is involved in the cardiovascular responses exhibited during Mev intoxication. |
In Sprague-Dawley rats, our results showed that microinjection bilaterally of Mev (10 nmol) into RVLM induced a progressive augmentation in NF-κB, PI3K, Akt or PTEN activity that paralleled the increase in NOS II or peroxynitrite level in RVLM. Loss-of-function manipulations that included pharmacological blockade, gene knockdown, or immunoneutralization of NF-κB, PI3K or Akt in RVLM significantly potentiated and prolonged the initial increase in “life-and-death” signal, reversed the cardiovascular depression, and blunted the augmented expression of NOS II or nitrotyrosine on induced by Mev. Blockade of PI3K or Akt in RVLM also significantly blunted the Mev-induced activation of NF-κB in the RVLM. However, immunoneutralization of PTEN in RVLM significantly diminished the increase in “life-and-death” signal and potentiated the increase in Akt activity. We conclude that the PI3K/Akt cascade plays a “pro-death” role in our Mev intoxication model of brain stem death by upregulating NF-κB/NOS II/peroxynitrite in the RVLM, subject to antagonism by PTEN in this process.
Microinjection bilaterally of Mev (10 nmol) into the RVLM induced a significantly augmentation in PKA activity in ventrolateral medulla that was not antagonized by coadministration of a nonselevtive or selective muscarinic receptor inhibitor. However, pharmacological blockade PKA in RVLM significantly blunted the initial increase in “life-and-death” signal and the accompanying augmentation of NOS I expression in the ventrolateral medulla exhibited during Mev intoxication. We conclude that a muscarinic receptor-independent activation of PKA plays a “pro-life” role in our Mev intoxication model of brain stem death by up regulating NOS I/PKG in the RVLM.
According to this study, we proved that Mev stimulates different mechanism, muscarinic receptor-independent/PKA and PI3K/Akt/NF-κB, to regulate NOS I and NOS II expression respectively, and induces cardiovascular responses during “pro-life” and “pro-death” phases. This information should provide further insights on the cellular mechanism of central cardiovascular regulation during the progression towards brain stem death, and offer news vistas in our search for therapeutic remedies or management strategies against fatal organophosphate poisoning and brain stem death.