Phrenic Motoneuron Expression Of Neurotrophins And Their Receptor Trkb Following Cervical C2 Spinal Cord Hemisection

In previous studies, we found that after cervical spinal cord hemisection at C2 (SH), neuromuscular transmission improved in the rat diaphragm muscle (DIAm). We also found that exogenous brain-derived neurotrophic factor (BDNF) treatment enhanced neuromuscular transmission, whereas inhibiting activation of its receptor (TrkB) worsened neuromuscular transmission. We hypothesized that expression of BDNF and/or its receptor TrkB at phrenic motoneurons would increase following SH. In the present study, adult male rats underwent SH or sham surgery. Phrenic motoneurons were labeled by injection of cholera toxin B into the DIAm and retrogradely-labeled phrenic motoneurons were sampled by laser capture microdissection (LCM). BDNF and TrkB receptor (truncated – T1 and full length – FL) mRNA were measured in LCM-microdissected motoneurons using quantitative real-time RT-PCR and expressed as a ratio to ribosomal S16 RNA. We found that BDNF mRNA expression in phrenic motoneurons increased by 3 days after SH (~2-fold). Similarly, both TrkB.T1 and TrkB.FL mRNA increased by 3 days after SH (~17- and ~11-fold, respectively). It is possible that the relative expression of neurotrophins and their receptors (truncated or full-length) may determine the time-course of restoration of phrenic activity following SH. Supported by NIH grants AR51173 and HL37680 and the Mayo Foundation.