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Transplantation of 11 day gestation rat fetal cortex and spinal cord into adult rat thoracic spinal cord is feasible. However, the techniques used at present for the implantation of the fetal transplant result in host spinal gray matter necrosis. One day after implantation the transplant is in a fluid-filled cyst in the host. The transplanted fetal tissue forms spherical neuroepithelia and unorganized cellular arrays. At Day 3 after transplantation the implant has sedimented to the ventral aspects of the fluid-filled cyst. By 10 days, there is an active neuroepithium with differentiating neurons and neuroglia lining the basal portion of the cyst. The transplant then proceeds to fill the cavity formed by host phagocytosis of the debris in the fluid-filled cyst.

Implants of various types of neuronal and nonneuronal tissue have shown promise for the amelioration of certain disorders of the adult mammalian brain. Implants may also have therapeutic potential for some lesions of the spinal cord. To examine the feasibility of implantation for clinically relevant spinal cord injuries, we have implanted cells into injury sites produced by a well-characterized and standardized rat model of contusive injury. To reduce the possibility of the implantation procedure itself causing damage to the spinal cord, the tissue was dissociated and a suspension of cells introduced into the cord via a small bore needle. To test the implantation procedure, dissociated adult rat dorsal root ganglia were used because of the ease with which these neurons could be distinguished after implantation. The extent to which functional deficits were produced or exacerbated by the implantation procedure was assessed by behavioral tests of groups of rats that had been implanted (implant controls), contused (injury only) or contused and implanted (injury-implant). Survival of the implanted neurons was assessed by quantitative morphological analysis of histological sections taken through the injury/implant sites at different times following injury. In addition, the histopathology of the contusive injury sites was compared for rats that had or had not received immediate or delayed implants. Results indicated that cell suspensions could be implanted into the spinal cord without causing a functional deficit in an otherwise uninjured animal or exacerbating a standardized incomplete contusive injury. Implanted neurons survived for at least 4 weeks in all contusion sites whether implantation was performed immediately following injury or after a delay of 1 week.(ABSTRACT TRUNCATED AT 250 WORDS)

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