Fluoro-Jade B stains quiescent and reactive astrocytes in the rodent spinal cord

In an attempt to label dying neurons in the injured spinal cord, we used the novel fluorescein derivative Fluoro-Jade B, which has been reported to specifically label dead or dying neurons in the brain. Rats and mice were subjected to a moderate level of spinal cord injury using an IH impact device and sacrificed at 1, 2, 4, 7, 14, and 21 days post injury. Spinal cord tissue was processed for Fluoro-Jade B histochemistry and included sections throughout the injured region of the cord. No Fluoro-Jade positive neurons were observed in sections from any time point postinjury at any level of the spinal cord. Instead, Fluoro-Jade labeled astrocytes in uninjured control animals and injured animals. The specificity of astrocytic staining was confirmed by co-localizaton of Fluoro-Jade with glial fibrillary acidic protein. We also subjected a group of rats to a sequential cortical contusion injury and spinal cord injury. Sections from these animals showed numerous Fluoro-Jade positive neurons in the hippocampal formation and thalamus underlying the cortical contusion; however, the staining pattern in the spinal cord was identical to those animals that had received spinal cord injury alone.