Short- and long-term effects of combined pre- and postnatal ethanol exposure (three trimester equivalency) on the development of myelin and axons in rat optic nerve.

This study evaluated the effects of a combined gestational and 10 day postnatal alcohol exposure (human three trimester equivalency) on the development of myelin and axons in rat optic nerve. Rats were exposed during gestation via liquid diet, then their artificially reared pups were further exposed for 10 postnatal days via an ethanol-containing diet fed by gastrostomy. Control animals from pair-fed dams were artificially reared for 10 days on pair-fed isocaloric diets. Anesthetized animals were perfused with fixative on gestational days (G) 15 and 20 and postnatal days (P) 5, 10, 15, 20, and 90, then optic nerve tissues prepared for electron microscopy. Optic nerve cross-sectional areas were generally less from G20 through P90 in ethanol exposed animals. Counts of the number of myelinated nerve fibers per unit area and of the numbers of fibers in different stages of myelin development revealed that alcohol exposure caused a delay in myelin acquisition at 10 and 15 days that was compensated for at 20 and 90 days. Myelin thickness as a function of axon diameter was decreased in the alcohol exposed animals from 10 through 90 days, indicating a permanent reduction in the relative thickness of myelin. These results show that alcohol exposure for all of gestation and 10 postnatal days in the rat (human three trimester equivalency) causes a permanent reduction in myelin thickness along with a delay in myelin acquisition in the optic nerve. Such alterations in developing and adult myelin could help to explain some of the neurological and visual dysfunctions associated with developmental alcohol exposures.