Decreased axonal calibres without axonal loss in optic nerve following chronic alcohol feeding in adult rats: a morphometric study.

The effects of chronic ethanol exposure on number and calibres of optic nerve axons (and number of retinal ganglion cells) were investigated in a rat model. Male Sprague-Dawley rats were fed a liquid, ethanol-containing diet for 5, 10 and 17 weeks with littermates given isocaloric amounts of ethanol-free diet serving as controls. After fixation by perfusion, the optic nerves were imbedded in epoxy resin and sectioned for electron microscopy. Systematic random sampling was made from a cross-shaped area over the nerve. Axons within a counting frame were counted and morphometrically categorized with regard to mean diameter and the total number of axons estimated from number per area and the cross-sectional area of the nerve, which was measured using a digitizer table. According to non-parametric statistical analysis, ethanol exposure resulted in a significant reduction in mean cross-sectional area of the optic nerve and in mean axonal calibre but not in total axonal number in the ethanol-treated rats but there was no significant effect of duration of the exposure. The mean cross-sectional area of the nerve was reduced by 9%, 10% and 18% after 5, 10 and 17 weeks of exposure, respectively. The reduction in cross-sectional area appeared to be related to a proportional reduction in axonal and myelin area fractions. The findings indicate that chronic ethanol exposure results in decreased axonal calibres without axonal loss. This also implies that there is no reduction in the number of retinal ganglion cells.