The Influence of Donor Age, Nerve Growth Factor, and Cografting with Drosophila Cells on Survival of Peripherally Grafted Embryonic or Fetal Rat Dorsal Root Ganglia

Abstract

Previous studies have shown that embryonic rat and human dorsal root ganglion (DRG) cells survive grafting to the cavity of extirpated adult rat DRG. Furthermore, grafted human embryonic neurons were shown to send axons peripherally and into the spinal cord, where they establish functional synaptic connections. This study analyzed the survival of orthotopically allografted rat DRG cells from embryonic stages 15 (E15) and 20 (E20), and the influence on their survival of nerve growth factor (NGF). NGF was delivered to the DRG transplants either by pump infusion or by cotransplantation of cells from Drosophila melanogaster, transgenic for human NGF. Lumbar DRGs of adult rats were removed and a collection of E15 or E20 DRGs placed in the cavity. One month after grafting the total number of DRG cells in the grafts was counted. Differentiation of subpopulations of DRG cells was estimated by counting cells immunostained for calcitonin gene-related peptide (CGRP), Griffonia simplicifolia agglutinin isolectin B4 (GSA), or heavy neurofilament protein (antibody RT97). The results show: i) similar survival of E15 and E20 grafts, with great variability in the survival of different subpopulations in E15 transplants, but a more consistent distribution of different phenotypes in E20 transplants; ii) infusion of NGF for 2 weeks increases the survival of E15 transplants, but has a negative effect on E20 transplants; iii) Drosophila cells transfected with human NGF gene survive peripheral xenografting and have a positive effect on the survival of the GSA- and CGRP-positive populations in E15 and E20 transplants; iv) Drosophila cells without the human NGF gene increase cell survival in E20 transplants. These data suggest that i) the effect of NGF is dependent on the embryonic stage of the transplants, ii) age-dependent sensitivity to NGF influences graft survival, and iii) transgenic Drosophila cells can be cotransplanted with embryonic neural tissue to the mammalian peripheral nervous system with a positive effect on the survival of neural grafts.