ASTROCYTES AND OLIGODENDROCYTES REACTIONS AFTER A TOTAL SECTION OF THE RAT SPINAL-CORD

Regeneration after an injury in the Central Nervous System is dependen t on intrinsic and extrinsic factors. Among the latter are the reactio ns of glial cells. Using the model of total section of adult rat spina l cord, we have studied the spatial and temporal responses of astrocyt es and oligodendrocytes to the lesion of spinal cord axons. We studied at molecular and cellular levels the specific markers GFAP (glial fib rillary acidic protein) for the astrocytes, CNP (2'-3' cyclic 3' nucle otide phosphodiesterase) which is principally expressed by immature ol igodendrocytes, and MBP (myelin basic protein) implicated later in the myelin compaction, and which is more specific of mature oligodendrocy tes. After injury, all astrocytes, but more markedly those of the grey matter, reacted by an increase of GFAP messenger and protein. This in crease was very rapid for messenger, and peaked at 3 days. This increa se was more protracted for the protein and persisted after 3 weeks. Me ssenger increase is more marked and more protracted below than above t he lesion. Oligodendrocytes also reacted quickly by an increase of CNP and MBP messengers. For CNP, both messenger and protein increased rap idly and returned to control level after 1 week. MBP showed the same t ime course of changes, with lower and slower decrease above the lesion . Counts of oligodendrocytes showed that the percentage of the less ma ture form (light oligodendrocytes) increased dramatically above and be low the lesion. After 1 week, above the lesion, this percentage was we ll below that of the control, whereas below the lesion, it reverted to control value. These results indicate that, following a lesion, astro cytes react quickly and intensely, but more so below the lesion; oligo dendrocytes resume a sequence of maturation which is eventually comple ted above the lesion where remyelinisation can occur and which is prem aturely interrupted below the lesion. However, intact oligodendrocytes persist below the lesion, where they constitute a potential for remye linisation of regenerated and/or transplanted axons. (C) 1998 Elsevier Science B.V.