Evaluation of blood vessel and neurite growth into a collagen matrix placed within a surgically created gap in rat spinal cord.

A complete gap of 3-4 mm was surgically created in the spinal cord of adult rats between the T8-T10 vertebral level, filled with a collagen matrix and closed with sutures. Animals were killed at weekly intervals from 14 to 42 days postimplantation. The collagen implant (CI) was evaluated for ingrowth of blood vessels and neurites using light and electron microscopic techniques. At 42 days postimplantation, 3 CI animals underwent a transection at the rostro-caudal center of the CI followed by placement of horseradish peroxidase (HRP)-impregnated filter paper between the cut ends. The number and location of HRP-labeled cells in CI animals were compared to normal animals that received a spinal cord transection at the T9 vertebral level immediately followed by placement of HRP between the cut stumps of spinal cord. Connective tissue (CT) septae, neurites and blood vessels invaded the CI from adjacent spinal neuropil and surrounding CT capsule. CI animals revealed HRP-labeled cells in the intermediolateral cell column (IML), parabrachial nuclei, locus coeruleus and red nucleus with a preponderance of labeled cells found in the IML rostral to the CI. In contrast, no IML were labeled in thoracic spinal cord rostral to HRP implantation in control animals. It was concluded that the above brainstem nuclei, which normally project axons into spinal cord, are capable of extending their severed axons into the CI following spinal cord injury and that uninjured IML cells also sprout axons into the CI.