SPINAL-CORD SKELETAL-MUSCLE COGRAFTS - TROPHIC AND FUNCTIONAL INTERACTIONS

Skeletal muscle from embryonic day 20 (E20) was combined with E15 rat spinal cord in the anterior chamber of the eye of adult albino rats. T he two grafts were either transplanted concomitantly or sequentially, in which case muscle tissue was added 4 months after the spinal cord. Control groups received a single graft of either spinal cord or skelet al muscle. Survival and intraocular growth were observed through the c ornea. After maturation in oculo, the double grafts were examined immu nohistologically utilizing antisera to neurofilament (NF) and acetylch olinesterase (AChE). The grafts were also evaluated using electrical s timulation to determine functional connectivity. The spinal cord and s keletal muscle grafts were found to exert reciprocal trophic effects o n each other, evidenced as a larger muscle mass in skeletal muscle gra fts allowed to develop in the presence of spinal cord tissue, and a la rger volume of spinal cord grafts allowed to develop together with a s keletal muscle graft, respectively. Immunohistochemistry revealed NF-p ositive nerve fibers leaving the spinal cord graft and entering the mu scle tissue. AChE-positive endplates developed in the muscle grafts. E lectrical stimulation of the spinal cord part of double-graft combinat ions generally elicited contractile responses in specific areas of the muscle cograft. These results demonstrate both structural and functio nal connections between grafts of spinal cord and skeletal muscle tiss ue in vivo. The fact that such connections were also established betwe en a mature (adult) spinal cord graft and fetal skeletal muscle tissue suggests that some alpha-motoneurons are able to survive for many mon ths in the intraocular grafts without an appropriate target, and that they are able to subsequently innervate skeletal muscle targets.