MYELIN-ASSOCIATED NEURITE GROWTH-INHIBITORY PROTEINS AND SUPPRESSION OF REGENERATION OF IMMATURE MAMMALIAN SPINAL-CORD IN CULTURE

Neurite outgrowth across spinal cord lesions in vitro is rapid in prep arations isolated from the neonatal opossum Monodelphis domestica up t o the age of 12 days, At this age oligodendrocytes, myelin, and astroc ytes develop and regeneration ceases to occur, The role of myelin-asso ciated neurite growth-inhibitory proteins, which increase in concentra tion at 10-13 days, was investigated in culture by applying the antibo dy IN-1, which blocks their effects. In the presence of IN-1, 22 out o f 39 preparations from animals aged 13-17 days showed clear outgrowth of processes into crushes. When 34 preparations from 13-day-old animal s were crushed and cultured without antibody, no axons grew into the l esion. The success rate with IN-1 was comparable to that seen in young er animals but the outgrowth was less profuse, IN-1 was shown by immun ocytochemistry to penetrate the spinal cord, Other antibodies which pe netrated the 13-day cord failed to promote fiber outgrowth, To disting uish between regeneration by cut neurites and outgrowth by developing uncut neurites, fibers in the ventral fasciculus were prelabeled with carbocyanine dyes and subsequently injured. The presence of labeled fi bers in the lesion indicated that IN-1 promoted regeneration, These re sults show that the development of myelin-associated growth-inhibitory proteins contributes to the loss of regeneration as the mammalian cen tral nervous system matures. The definition of a critical period for r egeneration, coupled with the ability to apply trophic as well as inhi bitory molecules to the culture, can permit quantitative assessment of molecular interactions that promote spinal cord regeneration.