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Phrenic long‐term facilitation (pLTF) following acute intermittent hypoxia (AIH) is TrkB and PI3K/Akt dependent in rats with motor neuron death from intrapleural CTB‐saporin injections
Author(s) -
Nichols Nicole L.,
Tanner Miles
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.1053.13
Subject(s) - saporin , pi3k/akt/mtor pathway , phrenic nerve , intermittent hypoxia , protein kinase b , tropomyosin receptor kinase b , medicine , motor neuron , pharmacology , respiratory system , anesthesia , receptor , biology , neuroscience , neurotrophic factors , spinal cord , immunology , signal transduction , microbiology and biotechnology , immunotoxin , monoclonal antibody , antibody , obstructive sleep apnea
Intrapleural injections of cholera toxin B fragment conjugated to saporin (CTB‐SAP) selectively kills respiratory motor neurons, and mimics motor neuron death observed in rats with amyotrophic lateral sclerosis (ALS) (Nichols et al., 2015). This CTB‐SAP model allows us to study the impact of respiratory motor neuron death on breathing without many complications attendant to ALS, and is sufficient to enhance phrenic long‐term facilitation (pLTF, a form of phrenic motor facilitation; Nichols and Mitchell, ibid , 2014) after 7 days of CTB‐SAP (CTB‐SAP 145±22%; control 54±5%). However, the mechanism responsible for this enhancement is unknown. pLTF in naïve rats predominately requires 5HT 2 receptors, the new synthesis of BDNF, and MEK/ERK signaling; however, there is an alternative mechanism for pLTF that requires A 2A receptors, the new synthesis of TrkB, and PI3K/Akt signaling. Preliminary data suggest that A 2A receptors are increased in the phrenic motor nucleus of CTB‐SAP treated rats (Craig et al., ibid ) suggesting that CTB‐SAP rats utilize the alternative mechanism for pLTF. Here, we tested the hypothesis that pLTF is TrkB and PI3K/Akt, not BDNF and MEK/ERK, dependent in anesthetized, paralyzed and ventilated adult Sprague Dawley rats. Specifically, AIH (3, 5 min bouts of 10.5% O 2 ) induced pLTF was studied 7 days following bilateral, intrapleural injections of: 1) CTB‐SAP (25μg), or 2) un‐conjugated CTB and SAP (control). Intrathecal C 4 delivery included either: 1) small interfering RNA that targeted BDNF or TrkB mRNA; 2) U0126 (MEK/ERK inhibitor); or 3) PI828 (PI3K/Akt inhibitor). Our preliminary data suggest that pLTF in CTB‐SAP treated rats is TrkB dependent (siTrkB: 1%, n = 1; siBDNF: 127%, n=1), whereas pLTF in controls is BDNF dependent (siTrkB: 35%, n = 1; siBDNF: 11%, n=1). U0126, not PI828, nearly abolished pLTF in controls (U0126: 13%, n=2; PI828: 52%, n=2); in contrast, pLTF was attenuated in CTB‐SAP treated rats following U0126 and PI828 (U0126: 71%, n=2; PI828: 85%, n=2). This suggests that CTB‐SAP treated rats express pLTF primarily via an alternative mechanism that requires the new synthesis of TrkB and both MEK/ERK and PI3K/Akt signaling. Future studies will be focused on completing this analysis and testing whether pLTF in CTB‐SAP treated rats is abolished following C 4 intrathecal, A 2A receptor antagonist treatment. This project increases our understanding of respiratory plasticity and its implications for breathing following motor neuron death. Support or Funding Information Supported by NIH K99/R00 HL119606