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Adeno‐associated viral delivery of TrkB receptor enhances functional recovery after cervical spinal hemisection

Unilateral C2 spinal cord hemisection (C2SH) removes premotor drive to phrenic motoneurons, paralyzing the ipsilateral diaphragm muscle (DIAm). In previous studies, we found that intrathecal brain‐derived neurotrophic factor (BDNF) increases the proportion of rats displaying recovery of ipsilateral DIAm activity over time. We hypothesized that enhancing expression of the tropomyosin‐related kinase receptor subtype B (TrkB) in phrenic motoneurons will promote functional recovery ipsilateral to C2SH. Adult rats were injected intrapleurally with AAV7 expressing TrkB.FL‐FLAG, and 3 weeks later C2SH was performed. A separate group of C2SH animals served as controls. Bilateral DIAm EMG activity was chronically monitored to assess recovery up to 2 weeks after C2SH. In AAV‐treated rats, delivery of TrkB.FL‐FLAG to phrenic motoneurons was evident by the presence of FLAG protein in the phrenic motor nucleus. At 7‐days post‐C2SH, the proportion of rats displaying ipsilateral DIAm EMG activity was 13% and 40% in the untreated control and AAV‐treated groups, respectively. At 14‐days post‐C2SH, all AAV‐treated rats displayed functional recovery compared to 40% of C2SH rats. We conclude that targeted delivery of TrkB.FL to phrenic motoneurons enhances functional recovery of DIAm respiratory activity following upper cervical spinal cord injury.