Ultrastructural investigation into the influence of ethanol on synaptic maturation in rat neocortex. I. Qualitative assessment.

Male rats were exposed daily to ethanol vapour 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, and ethanol-rehabilitated animals were examined at 56 and 76 days postnatally. Tissue from the parietal cortex of each animal stained with osmium tetroxide and with ethanolic-phosphotungstic acid (E-PTA) was analyzed by qualitative ultrastructural techniques. The ethanol flow rate in the incubation chamber was adjusted to maintain the blood ethanol level as close as possible to 0.1 g/100 ml. Ethanol-treated rats weighed less than ethanol-rehabilitated animals at days 56 and 76. At day 7 synapses were formed between axons and dendritic growth cones, dendritic shafts and filopodia in control and ethanol-treated tissue. At days 14 and 21 well-developed axodendritic and axospinous synapses were evident in both groups. The neuropil of 56- and 76-day-old material was similar in the control and treatment groups, except that there was an enlargement of dendritic profiles in the 56-day-old ethanol-treated material. Perforated synapses were most common in 56-day-old ethanol-treated material, with degenerating synapses most common in 56-day-old (and to a lesser extent 76-day-old) ethanol-rehabilitated material. No obvious differences were detected between any of the groups of the E-PTA-stained material. The presence of degenerating and perforated synapses suggests that synaptic remodelling is occurring, and this may be a means of adapting synaptic mechanisms to the functional demands imposed by ethanol.