POSTNATAL-DEVELOPMENT OF THE OPTIC-NERVE IN (C57BLXCBA)F1 HYBRID MICE- GENERAL CHANGES IN MORPHOMETRIC PARAMETERS

A morphometric analysis of the optic nerve in different age groups of (C57BL x CBA)F1 hybrid mice was carried out. Morphometric parameters e xamined were mean nerve cross-sectional area (csa), mean myelinated ne rve fibre count, mean myelinated nerve fibre density and myelinated ne rve fibre size distribution. The findings revealed that the optic nerv e continues to develop well into adult life. Growth in calibre was ver y rapid during the early stage of postnatal life, but progressively sl owed with age thereafter. No myelinated nerve fibres were observed bef ore the 5th day of postnatal life. Similarly, once myelination was ini tiated, it progressed very rapidly during the early stage of postnatal development and, as for the csa, it slowed thereafter. Peak level of myelination within the optic nerve, which corresponded with the age wh en the maximum number of myelinated nerve fibres, i.e. 94213 +/- 1799 (S.E.M.) was measured, occurred at the 16th week of postnatal life. Th e earliest myelinated nerve fibres seen were predominantly large in di ameter, but with increasing age, fibres of smaller diameter dominated the myelinated nerve fibre spectrum in the nerve. The highest mean mye linated nerve fibre density was observed in mice at the age of peak my elination.