Grafted fetal astrocyte migration can prevent host neuronal atrophy: comparison of astrocytes from cultures and whole piece donors

Abstract

In a ‘double blind’ study, 2 series of adult rats were trained to traverse a narrow bar or a horizontal ladder for a water reward. Hindlimb placement (measured as hindlimb foot slips) of the subjects trained on the narrow platform was ranked. The subjects traversing the ladder were videotaped and the number of hindlimb slips counted. After reaching criterion (10 complete traverses on each of 2 consecutive days), all animals had the fasciculus gracilis (FG) of the third cervical spinal cord segment (C₃) aspirated to sever hindlimb dorsal column afferents. After aspiration of C3FG the subjects were randomly placed in an aspiration-only (controls) or aspiration + graft group. All grafts were prelabeled with the plant lectin Phaseolus vulgaris leucoagglutinin (PHAL) as a graft-derived cell marker. The grafts were either unoriented whole pieces of E14 fetal spinal cord or 10⁵ purified, cultured, E14 fetal spinal cord astrocytes. Subjects were tested at intervals over 90 days. Aspiration of C3FG and a graft of whole pieces of E14 fetal spinal cord resulted in a statistically significant improvement in hindlimb placement at 21 and 90 days (P < 0.05) when compared to controls. In contrast, animals with cultured, purified, E14 fetal spinal cord astrocyte grafts had significantly worse (P < 0.05) hindlimb placement than controls. Immunohistochemical double staining for PHAL and glial fibrillary acidic protein in the same cell showed that astrocytes from both types of grafts migrated to the nucleus gracilis (NG) of the medulla of the host. The grafted fetal astrocytes from the whole piece grafts prevented denervation atrophy of the host NG neurons, whereas cultured grafted fetal astrocytes did not demonstrate this effect. After grafting donor tissue that contained astrocytes into the injured spinal cord there were two accompanying classes of astrocytes. One class derived from whole piece, E14, fetal spinal cord grafts migrated to the NG of the host, prevented atrophy of host NG cluster and interneurons, and improved hindlimb placement. The other class, derived from cultures of E14 fetal spinal cord astrocytes, migrated to the NG of the host, failed to maintain the size of cluster neurons and interneurons of the host NG, and resulted in a greater hindlimb placement deficit when compared to controls. These data suggest that improvement of hindlimb placement due to graft-derived fetal astrocytes in injured host spinal cord was due to the ability of the astrocytes to maintain host neurons and neuronal networks.