Intrapleural siRNAs targeting TrkB attenuate acute intermittent hypoxia (AIH)‐induced phrenic long‐term facilitation (pLTF)

Abstract

Activation of cervical spinal TrkB (the high affinity BDNF receptor) is necessary for pLTF (Baker‐Herman et al., Nature Neurosci, 2004), a long‐lasting increase in phrenic motor output following AIH. However, the specific cell type expressing relevant TrkB receptors is not yet known. Here, we tested the hypothesis that relevant TrkB receptors are expressed in phrenic motor neurons using a novel RNAi technique to knock down TrkB specifically within phrenic motor neurons (Mantilla et al., 2012). Adult, male, Sprague‐Dawley rats received successive intrapleural injections (3 days) of: 1) vehicle (30uL/side; n=2); 2) siRNAs targeting TrkB mRNA (30uL, 100pmol/side; n=6), 3) siPKCζ, a molecule involved in other forms of phrenic plasticity, but not pLTF (30uL, 100pmol/side; n=1), or 4) no treatment (n=6). One day later, anesthetized, paralyzed and ventilated rats were given AIH or normoxia. Vehicle (49%) and uninjected rats (51% ±14%) exhibited pLTF 60 min post‐AIH (p<0.05). Intrapleural siTrkB attenuated pLTF (20%±16%; p<0.05 vs. other treatments), whereas siPKCζ did not (68%). Although experimental verification of selective TrkB knock‐down is necessary, these preliminary data strongly suggest that the TrkB receptors relevant for pLTF are expressed in phrenic motor neurons.