A. Representative examples of airflow traces recorded in unanesthetized rats and used to derive breathing frequency (F), tidal volume (TV) and minute ventilation ( E). Two different time scales are provided - the arrows in the expanded traces point to individual breaths indicated by downward traces (i.e. negative airflow). Scaling is the same in the Pre-C2Hx and 12 wk post-C2Hx traces; airflow is in units of ml/sec. Note the rapid, shallow pattern of breathing during the baseline condition after C2Hx as indicated by the increase in breathing frequency and the reduction in airflow. The mean baseline F (B), TV (C), and E (D) responses to injury were not different between C2Hx, FSC_V and FSC_D rats nor were there any differences in E during respiratory challenge (E). Examples of efferent phrenic bursting recorded in anesthetized rats at 12 wks post-injury are provided in panel F. The arrows indicate relatively weak bursting at baseline in the FSC_V rat. There was a tendency for ipsilateral (IL) ∫Phr amplitude to be reduced in FSV_D rats during challenge (P=0.06, G). Phrenic burst frequency (F) was enhanced in FSC_V rats (H). Contralateral (CL) Phr was similar between groups (I). Mean arterial pressure (MAP) was reduced in FSC_V rats during baseline (J). Symbols: ■-FSC_V, ◆-FSC_D, ●-C2Hx, ↓O₂-hypoxia, ↑CO₂-hypercapnia

A. Schematic diagram of the tissue microdissection procedure employed. A rostro-caudal incision was made along the midline of spinal cord separating it into two halves (Ai). From this, the dorsal- and ventral-most parts of the tissue (from the alar and basal plates, respectively) were then removed to obtain strips of tissue for transplantation (Aii, FSC_D and FSC_V). B. Transverse sections (2μm) of adult spinal cord stained with toluidine blue, at the lesion/transplant epicenter 2 months post-C2Hx. These images demonstrate the growth of transplanted tissue (left half of each section). C. Higher magnification images reveal that FSC transplants retain some developmental cues, with the formation of clusters of small neurons into myelin-free, SG-like regions (SG) in FSC_D, and the presence of large bands of white matter (arrowheads) throughout FSC_V. Measurement of the proportion of SG-like regions (±SD) in these animals confirms a significantly greater prevalence in FSC_D recipients. D. Transverse sections (40 μm) immunolabeled for NeuN demonstrates the large number of mature neurons throughout the graft in both FSC_D and FSC_V recipients. These sections also show the similarity between the clusters of small neurons into SG-like regions (SG) and the host SG (SG_H). E. In a subset of animals the phrenic circuit ipsilateral to C2Hx was retrogradely traced with a transynaptic tracer (PRV). Longitudinal sections of spinal cord at the level of the ventral horns showing host and transplant. The dotted line is an approximation of the interface between host and graft tissue. Immunolabeling for PRV reveals labeled phrenic motoneurons (PhMN) and cells within FSC_D and FSC_V transplants. This suggests that donor neurons become synaptically integrated with the host phrenic circuit and provides an anatomical basis for how these cells may influence ipsilateral phrenic activity.