Postnatal development of the optic nerve in (C57BL x CBA)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 examined were mean nerve cross-sectional area (csa), mean myelinated nerve fibre count, mean myelinated nerve fibre density and myelinated nerve fibre size distribution. The findings revealed that the optic nerve continues to develop well into adult life. Growth in calibre was very rapid during the early stage of postnatal life, but progressively slowed with age thereafter. No myelinated nerve fibres were observed before the 5th day of postnatal life. Similarly, once myelination was initiated, 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 when the maximum number of myelinated nerve fibres, i.e. 94213 +/- 1799 (S.E.M.) was measured, occurred at the 16th week of postnatal life. The earliest myelinated nerve fibres seen were predominantly large in diameter, but with increasing age, fibres of smaller diameter dominated the myelinated nerve fibre spectrum in the nerve. The highest mean myelinated nerve fibre density was observed in mice at the age of peak myelination.