Visual system abnormalities are commonly encountered in the fetal alcohol syndrome although the level of
exposure at which they become manifest is uncertain. In this study we have examined the effects of either
low (ETLD) or high dose (ETHD) ethanol, given between postnatal days 4–9, on the axons of the rat optic
nerve. Rats were exposed to ethanol vapour in a special chamber for a period of 3 h per day during the
treatment period. The blood alcohol concentration in the ETLD animals averaged ∼ 171 mg/dl and in the
ETHD animals ∼ 430 mg/dl at the end of the treatment on any given day. Groups of 10 and 30-d-old
mother-reared control (MRC), separation control (SC), ETLD and ETHD rats were anaesthetised with an
intraperitoneal injection of ketamine and xylazine, and killed by intracardiac perfusion with phosphate-buffered glutaraldehyde. In the 10-d-old rat optic nerves there was a total of ∼ 145000–165000 axons in
MRC, SC and ETLD animals. About 4% of these fibres were myelinated. The differences between these
groups were not statistically significant. However, the 10-d-old ETHD animals had only about 75000 optic
nerve axons (P < 0.05) of which about 2.8% were myelinated. By 30 d of age there was a total of between
75000–90000 optic nerve axons, irrespective of the group examined. The proportion of axons which were
myelinated at this age was still significantly lower (P < 0.001) in the ETHD animals (∼ 77%) than in the
other groups (about 98%). It is concluded that the normal stages of development and maturation of the rat
optic nerve axons, as assessed in this study, can be severely compromised by exposure to a relatively high
(but not low) dose of ethanol between postnatal d 4 and 9.