AAV-BDNF modulates 5HT2A receptor, glycine receptor subunits, and Nav1.1 channel gene expression in lumbar motoneurons after spinal cord injury

BACKGROUND: Proper excitability of spinal motor neurons (MNs) is essential for motor output. Spinal cord injury (SCI) disrupts this network and compromises MN- driven skeletal muscle contractions. We previously showed that tracer-identified MNs innervating ankle extensor and flexor muscles display gene-expression changes toward a more excitatory profile at 2 weeks post-lesion in rats, however, this shift does not restore stepping. Given evidence that brain-derived neurotrophic factor (BDNF) enhances MN excitability and promotes functional recovery, we investigated its effects on gene expression following SCI. METHODS: Adult male rats received retrograde tracers in gastrocnemius lateralis (GL) and tibialis anterior (TA) muscles. Two weeks later, complete low-thoracic transection was followed by bilateral lumbar L1-L2 injection of AAV-BDNF or PBS. Locomotion was assessed on a treadmill and in an open field. BDNF and TrkB transcripts were assessed by RNAscope, while selected receptor, transporter, and ion-channel transcripts were measured in lumbar segments and laser-microdissected GL and TA MNs by RT-qPCR. RESULTS: At two weeks, AAV-BDNF increased spinal BDNF transcript levels and restored TrkB transcripts in lumbar MNs. It improved treadmill locomotion with plantar placement, alternating step-like movements, and body-weight support, while open-field hindlimb movements were also improved. BDNF selectively increased Htr2a transcripts, particularly in GL MNs, and reduced glycine receptor subunit transcripts. It also reversed SCT-induced Scn1a upregulation in GL and TA MNs. Changes in glutamatergic and GABAA receptor transcripts were selective and MN-population dependent. CONCLUSIONS: These findings show that intraspinal AAV-BDNF is associated with locomotor recovery and transcriptional changes in MN excitability-related genes. The results support a role for BDNF in spinal circuit reactivation after SCT.