MORPHOMETRIC ANALYSIS OF MYELINATED FIBER COMPOSITION IN THE OPTIC-NERVE OF ADULT C57BL AND CBA STRAIN MICE AND (C57BL X CBA) F1-HYBRID - ACOMPARISON OF INTERSTRAIN VARIATION

In a study involving 50 optic nerves isolated from 3 different strains of adult male mice, (57BL, CBA and (C57BL x CBA) F1 hybrids, and from adult female CBA strain mice, we observed that the mouse had a lower mean total myelinated nerve fibre count than other mammals such as the rat, cat, rabbit, monkey and man where similar information was availa ble from the literature. The nerve fibre spectrum, however, which most ly consisted of small diameter fibres, was similar to the distribution seen in these other species. The largest myelinated nerve fibres obse rved in any of the strains of mice investigated had a diameter of not more than 1.92 mu m. The C57BL optic nerve had the largest population of large diameter fibres, while the F1 had the largest population of s mall diameter fibres. In all the strains of mice investigated, the dis tribution of nerve fibres was unimodal, with a modal diameter of 0.48 mu m. The mean nerve fibre diameter was 0.62+/-0.02 mu m (S.E.M.), 0.5 7+/-0.03 mu m and 0.55)+/-0.01 mu m for C57BL, F1 and CBA, respectivel y. The F1 had the lowest population of fibres around the modal diamete r. The myelinated nerve fibres were most densely packed in the CBA str ain of mice, whereas the C57BL was the least densely populated. There was a significant interstrain difference in the parameters measured be tween the 3 strains of mice studied, whereas there was no significant intrastrain difference.