Respiratory outcomes after mid-cervical transplantation of embryonic medullary cells in rats with cervical spinal cord injury

Respiratory motor output after cervical spinal cord injury (cSCI) is profoundly influenced by spinal serotonin. We hypothesized that intraspinal transplantation of embryonic midline brainstem (MB) cells rich in serotonergic raphé neurons would improve respiratory outcomes after cSCI. One week after hemisection of the 2nd cervical segment (C2Hx) a suspension of either embryonic (E14) MB cells, fetal spinal cord cells (FSC), or media only (sham) was delivered to the dorsal C3 spinal cord of adult male rats. Six weeks later, ventilation was evaluated using plethysmography; phrenic nerve activity was evaluated in a subset of rats. Seven of 12 rats receiving MB-derived grafts had clear histological evidence of serotonin-positive neurons in the C3-4 dorsal white matter. The transplantations had no impact on baseline breathing patterns, but during a brief respiratory challenge (7% inspired CO₂) rats with successful MB grafts had increased ventilation compared to rats with failed MB grafts, FSC or sham grafts. Recordings from the phrenic nerve ipsilateral to C2Hx also indicated increased output during respiratory challenge in rats with successful MB grafts. We conclude that intraspinal allografting of E14 MB cells can have a positive impact on respiratory motor recovery following high cSCI.