Grafting embryonic raphe neurons reestablishes serotonergic regulation of sympathetic activity to improve cardiovascular function after spinal cord injury

Cardiovascular dysfunction often occurs after high-level spinal cord injury (SCI). Disrupting supraspinal vasomotor pathways affects basal hemodynamics and contributes to the development of autonomic dysreflexia (AD). Transplantation of early stage neurons to the injured cord may reconstruct the descending projections to enhance cardiovascular performance. To determine the specific role of reestablishing serotonergic regulation of hemodynamics, we implanted serotonergic (5-HT+) neuron enriched embryonic raphe nucleus-derived neural stem cells/progenitors (RN-NSCs) into a complete spinal cord transection lesion site in adult female rats. Grafting embryonic spinal cord-derived NSCs (SC-NSCs) or injury alone served as two controls. Ten weeks post-injury/grafting, histological analysis revealed well-survived grafts and partial integration with host tissues in the lesion site. Numerous graft-derived serotonergic axons topographically projected to the caudal autonomic regions. Neuronal tracing showed that host supraspinal vasomotor pathways regenerated into the graft, and 5-HT+ neurons within graft and host brainstem neurons were transsynaptically labeled by injecting pseudorabies virus (PRV-614) into the kidney, indicating reconnected serotonergic circuits regulating autonomic activity. Using an implanted telemeter to record cardiovascular parameters, grafting RN-NSCs restored resting mean arterial pressure (MAP) to normal levels and remarkably alleviated naturally-occurring and colorectal distension-induced AD. Subsequent pharmacological blockade of 5-HT2A receptors with ketanserin in RN-NSC grafted rats reduced resting MAP and increased heart rate in all but two controls. Furthermore, spinal cord re-transection below RN-NSC grafts partially eliminated the recovery in AD. Collectively, these data indicate that RN-NSCs grafted into an SCI site relay supraspinal control of serotonergic regulation for sympathetic activity to improve cardiovascular function.