Prenatal exposure to low levels of carbon monoxide alters sciatic nerve myelination in rat offspring

Prenatal exposure to low concentrations of carbon monoxide (CO, 75 and 150 ppm from day 0 to day 20 of gestation), resulting in maternal blood HbCO co ncentrations equivalent to those maintained by human cigarette smokers, lea ds to subtle myelin alterations in the sciatic nerve of male rat offspring. The rapid growth spurt in pup body weight was related to the period of max imal increase in myelin sheath thickness in both control and GO-exposed ani mals. A significant reduction in myelin sheath thickness of sciatic nerve f ibers, paralleled by changes in the frequency distribution, occurred in bot h 40- and 90-day-old rats exposed in utero to CO (75 and 150 ppm), Myelin d eficit observed in 75 and 150 ppm GO-exposed animals showed up only after t he major spurt in myelination but not early during development. The subtle myelin alterations observed in GO-exposed offspring were not accompanied by changes in developmental pattern of axon diameters and did not result in a gross impairment of motor activity, These results suggest that the myelina tion process is selectively targeted by a prenatal exposure model simulatin g the CO exposure observed in human cigarette smokers. (C) 2000 Elsevier Sc ience Inc. All rights reserved.