Spinal Transection Induces Widespread Proliferation of Cells along the Length of the Spinal Cord in a Weakly Electric Fish

The ability to regenerate spinal cord tissue after tail amputation has been well studied in several species of teleost fish. The present study examined the proliferation and survival of cells following complete spinal cord transection rather than tail amputation in the weakly electric fish Apteronotus leptorhynchus. To quantify cell proliferation along the length of the spinal cord, fish were given a single bromodeoxyuridine (BrdU) injection immediately after spinal transection or sham surgery. Spinal transection significantly increased the density of BrdU⁺ cells along the entire length of the spinal cord at 1 day posttransection (dpt), and most newly generated cells survived up to 14 dpt. To examine longer-term survival of the newly proliferated cells, BrdU was injected for 5 days after the surgery, and fish were sacrificed at 14 or 30 dpt. Spinal transection significantly increased cell proliferation and/or survival, as indicated by an elevated density of BrdU⁺ cells in the spinal cords of spinally transected compared to sham-operated and intact fish. At 14 dpt, BrdU⁺ cells were abundant at all levels of the spinal cord. By 30 dpt, the density of BrdU⁺ cells had decreased at all levels of the spinal cord except at the tip of the tail. Thus, newly generated cells in the caudal-most segment of the spinal cord survived longer than those in more rostral segments. Our findings indicate that spinal cord transection stimulates widespread cellular proliferation; however, there were regional differences in the survival of the newly generated cells.