THE CRITICAL PERIOD FOR REPAIR OF CNS OF NEONATAL OPOSSUM (MONODELPHIS-DOMESTICA) IN CULTURE - CORRELATION WITH DEVELOPMENT OF GLIAL-CELLS,MYELIN AND GROWTH-INHIBITORY MOLECULES

A comparison was made of neurite growth across spinal cord lesions in the isolated central nervous system (CNS) of newborn opossums (Monodel phis domestica) at various stages of development. The aim was to defin e the critical period at which growth after injury ceases to occur, wi th emphasis on growth-inhibitory proteins, myelin and glial cells. In postnatal opossums 3-6 days old (P3-6), repair was observed 5 days aft er lesions were made in culture at the cervical level (C7) by crushing with forceps. Through-conduction of action potentials was re-establis hed and axons stained by Dir grew into and beyond the crush. in a seri es of 66 animals 29 showed repair. In 28 animals at P11-12 with compar able lesions repair was observed in five preparations. At P13-14, the CNS was still viable in culture, but none of the 25 preparations exami ned showed any axonal growth into the crush or conduction through it. The rostro-caudal gradient of development permitted lesions to be made in mature cervical and immature lumbar regions of P11-12 spinal cord. Growth across crushes occurred in lumbar but not in cervical segments of the same preparation. The development of glial cells and myelin wa s assessed by electron microscopy and by staining with specific antibo dies (Rip-1 and myelin-associated glycoprotein) in cervical segments o f neonatal P6-14 opossums. At P8, oligodendrocytes and thin myelin she aths started to appear followed at P9 by astrocytes stained with antib ody against glial fibrillary acidic protein. By P14, astrocytes, oligo dendrocytes and well-developed myelin sheaths were abundant. The cervi cal crush sites of P12 cords contained occasional astrocytes but no ol igodendrocytes. Specific antibodies (IN-1) to neurite growth-inhibitin g proteins (NI-35/250) associated with oligodendrocytes and myelin in the rat CNS cross-reacted with opossum proteins. Assays using the spre ading of 3T3 fibroblasts and IN-1 showed that by P7 inhibitory protein s became apparent, particularly in the hindbrain and cervical spinal c ord. The concentrations of NI-35/250 thereafter increased and became a bundant in the adult opossum. Our finding of a well-defined critical p eriod, encompassing only 5 days, in CNS preparations that can be maint ained in culture offers advantages for analysing mechanisms that promo te or prevent CNS repair.