Glutamatergic neurotransmission plays a role in BDNF/TrkB.FL‐induced enhancement of functional recovery after cervical spinal hemisection

Abstract

Brain‐derived neurotrophic factor (BDNF) acting through full‐length tropomyosin related kinase receptor subtype B (TrkB.FL) plays an important role in neuroplasticity following spinal cord injury. BDNF/TrkB.FL signaling in phrenic motoneurons is both necessary and sufficient to enhance spontaneous recovery of ipsilateral rhythmic phrenic activity after C2 spinal cord hemisection (SH), where premotor drive to phrenic motoneurons is removed. Phrenic motoneuron expression of the excitatory glutamatergic NMDA receptor correlates with the time course of spontaneous functional recovery post‐SH. We hypothesized that increased BDNF/TrkB.FL signaling in phrenic motoneurons enhances recovery of rhythmic phrenic activity after SH via regulation of glutamatergic receptor expression. Rats were injected intrapleurally with AAV7 expressing human TrkB.FL‐FLAG at 3 weeks prior to SH. FLAG was present in the cervical ventral horn region, and AAV7‐GFP expression was specifically in phrenic motoneurons. At 14 days post‐SH, quantitative real‐time RT‐PCR verified human TrkB.FL expression in microdissected phrenic motoneurons. Phrenic motoneuron expression of NMDA increased ~10 fold compared to control, suggesting that increased BDNF/TrkB.FL signaling magnified SH‐induced changes in phrenic motoneuron NMDA expression. Supported by HL96750 and T32‐HL105355, and Paralyzed Veterans of America.