SPROUTING AND REGENERATION OF LESIONED CORTICOSPINAL TRACT FIBERS IN THE ADULT-RAT SPINAL-CORD

We have studied the effects of tissue transplants and antibodies (IN-1 ) against the myelin-associated neurite growth inhibitory proteins on sprouting and regeneration of the rat corticospinal tract (CST). Trans plantation of embryonic spinal cord tissue into bilateral transection lesions of the lower thoracic spinal cord in young adult rats resulted in a marked increase of the sprouting of the lesioned CST. This sprou ting effect was probably elicited by soluble factors released from the transplants, and was enhanced by the IN-1 antibodies. The retraction of lesioned CST fibres normally observed with prolonged survival times was also reduced by the presence of transplants. In spite of these gr owth-promoting effects of the transplants, the regenerative elongation of CST sprouts into the caudal spinal cord was dependent upon the neu tralization of the myelin-associated inhibitory proteins. In the contr ols (no antibodies or control antibodies) only 27% of the animals show ed elongation of CST fibres exceeding the sprouting distance of 0.7 mm . These fibres grew to a maximal length of 1.8 mm (mean +/- SEM, 1.2 /- 0.1). In contrast, 60% of the IN-1-treated, transplant-containing r ats showed elongations of >0.7 mm, and these fibres grew up to 10.1 mm (4.6 +/- 0.5). Regenerating fibres crossed the lesion site through re maining tissue bridges. Neither embryonic spinal cord transplants nor a variety of implanted bridge materials could serve as a substrate for the regenerating CST axons.