NGF message and protein distribution in the injured rat spinal cord

Nerve growth factor (NGF) content of the spinal cord is increased after cord injury. NGF can cause central sprouting of sensory fibers after spinal cord injury (SCI), leading to autonomic dysfunction and pain. NGF also can promote the death of oligodendroglia after SCI. Knowing the source of intraspinal NGF would benefit strategies for minimizing abnormal plasticity and cell death after SCI. We identified these sources, using RNA in situ hybridization to detect NGF mRNA and double-labeling immunocytochemistry for NGF and cell-marking antigens. In uninjured and sham-injured rats, we identified NGF mRNA in leptomeningeal cells and in neurons in the intermediate grey matter, whereas NGF protein was observed only in leptomeningeal cells. At 3-7 days after transection or clip-compression SCI, NGF mRNA and protein were expressed in the lesion and throughout the intermediate grey matter and white matter rostral and caudal to the injury site. Transection-SCI was used to permit comparisons to previous studies; clip-compression injury was used as a more clinically relevant model. mRNA and protein in adjacent sections were expressed in ramified microglia, astrocytes, intermediate grey neurons, pial cells, and leptomeningeal and Schwann cells in the lateral white matter and the lesion site. Rounded macrophages in the lesion were immunoreactive (Ir) for NGF, but the cells expressing NGF mRNA were not in the same areas of the lesion and were not stained by a macrophage marker. Our data demonstrate that glia, neurons, meningeal cells and Schwann cells but not macrophages contribute to the increased intraspinal NGF after SCI.