When modeling effects of hypogravitation by the method of hindlimb unloading in rats the area of cross-section in lumbar part of a spinal cord was found to reduce. The analysis of spinal cord slides showed that these changes are associated with a decrease in the area of white substance of a spinal cord. Data obtained are consistent with our previous observation of a decrease in expression of the genes encoding myelin proteins. Results of our researches give the good reasons to believe that miyelinization failure in CNS is one of the factors that underlie the development of hypogravitational motor syndrome.