Ultrastructural investigation into the influence of ethanol on synaptic maturation in rat neocortex. II. Quantitative analysis.

Male rats were exposed to ethanol vapour daily from 3 days of age, and their brains were examined at 7, 14, 21, 56 and 76 days postnatally. Control animals were examined at each age, with ethanol-rehabilitated animals being examined at 56 and 76 postnatal days. Tissue, stained with osmium tetroxide and with ethanolic-phosphotungstic acid, from the parietal cortex of each animal was analyzed by quantitative ultrastructural techniques. Most of the statistically significant findings occurred at days 56 and 76. When compared with controls, ethanol-treated material at 56 days was characterized by a decrease in the number of synapses which were larger and more spherical, with a greater number of synaptic vesicles and a decrease in dense projections. At 76 days there was an increase in the percentage of axospinous-symmetrical terminals in the ethanol-treated population. In ethanol-rehabilitated tissue at 56 days the synaptic terminals were relatively immature, and were smaller, with a reduced number of synaptic vesicles coupled with an increase in large cisternae and with more positively curved junctions. By 76 days this material was practically indistinguishable from control tissue. It is proposed that at 56 days of age synaptic remodelling is under way in the ethanol-treated material, whereas following rehabilitation the terminals are relatively immature and appear to be actively functioning. Low to moderate levels of ethanol administered postnatally have a limited effect on synaptic maturation.