Effects of Sacrocaudal Spinal Cord Transection and Transplantation of Fetal Spinal Tissue on Withdrawal Reflexes of the Tail

Reflex responses to electrocutaneous stimulation of the tail were characterized in awake cats, before and after transection of the spinal cord at sacrocaudal levels S₃-Ca₁ Consistent with effects of spinal transection at higher levels, postoperative cutaneous reflexes were initially depressed, and the tail was flaccid. Recovery ensued over the course of 70–90 days after sacrocaudal transection. Preoperative and chronic postlesion reflexes elicited by electrocutaneous stimulation were graded in amplitude as a function of stimulus intensity. Chronic postlesion testing of electrocutaneous reflexes revealed greater than normal peak amplitudes, peak latencies, total amplitudes (power), and durations, particularly for higher stimulus intensities. Thus, sacrocaudal transection produced effects representative of the spastic syndrome. In contrast, exaggerated reflex responsivity did not develop for a group of cats that received transplants of fetal spinal cord tissue within sacrocaudal transection cavities at the time of injury, in conjunction with long-term immunosuppression by cyclosporine. We conclude that gray matter replacement and potential neuroprotective actions of the grafts and/or immunosuppression prevent development of the spastic syndrome. This argues that the spastic syndrome does not result entirely from interruption of long spinal pathways.