EXPRESSION OF MYELIN PROTEINS IN THE OPOSSUM OPTIC-NERVE - LATE APPEARANCE OF INHIBITORS IMPLICATES AN EARLIER NON-MYELIN FACTOR IN PREVENTING GANGLION-CELL REGENERATION

The pattern of appearance of myelin-associated proteins in the visual system of the Brazilian opossum Monodelphis domestica is described. Wh ole mounts of optic nerve, chiasm, and optic tract were sectioned hori zontally and incubated with antibodies to myelin basic protein (MBP), proteolipid protein (PLP), myelin-associated glycoprotein (MAG), ''Rip ,'' and the neurite inhibitory protein (IN-1), followed by visualizati on with diaminobenzidine and a peroxidase-conjugated secondary antibod y. PLP is first detectable 24 days after birth (P24) at the centre of the optic chiasm. MBP, MAG, Rip, and IN-1 appear first in the same are a at P26. By P28 the distribution of all proteins is similar, occupyin g the entire chiasm, optic tracts, and prechiasmatic portion of the op tic nerves. Protein expression progresses along the optic nerve to rea ch the lamina cribrosa by P34, coincident with the time of eye opening . A critical period in which the retinofugal pathway has a regenerativ e capacity has recently been observed in Monodelphis. This period ends at P12, 2 weeks before the appearance of the myelin-associated inhibi tory proteins MAG and IN-1. These results therefore suggest that regen eration in the developing retinofugal projection of the opossum is res tricted by an earlier non-myelin factor,which is in contrast to curren t literature on the spinal cord. (C) 1996 Wiley-Liss, Inc.