SELECTIVE-INHIBITION OF EARLY AXONAL REGENERATION BY MYELIN-ASSOCIATED GLYCOPROTEIN

When the distal stump of a transected peripheral nerve is brought: int o the vicinity of the proximal nerve stump, the regenerating axons adv ance toward it across the gap, Similar results are obtained when a pre degenerated nerve segment is used, However, when a nerve segment subje cted to proximal axotomy 7 days earlier (7-day nerve segment) was plac ed close to the proximal and of a freshly cut nerve at a distance of l ess than 1.5 mm, there were neither regenerating axons nor sprouts. Th e same inhibition of axonal regeneration was also exhibited when a ner ve segment subjected to axotomy 9 to 14 days earlier was used, To exam ine the inhibitory effect of the nerve segments on established regener ating axons, we positioned a 7-day nerve segment in close apposition t o a proximal nerve end at 2 or 3 days after transection. The growth of the 3-day-old regenerating axons, already ensheathed by Schwann cells , was not disturbed, but the 2-day-old regenerating axons, consisting of naked axons, were eliminated by the 7-day nerve segment, It is assu med that the findings reflect a mechanism serving to eliminate abundan t sprouts and immature axons, probably conferencing optimum regenerati on and maturation of outgrowing pioneer axons, The inhibitory effect o n abundant sprouts and immature axons was completely blocked by local application of antibodies to myelin-associated glycoprotein (MAG), The MAG-containing cells appeared at 6 to 12 days after axotomy. (C) Acad emic Press.