Poor myelination in the central nervous system of "dilute-lethal mutant mice" (d1/d1).

The activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase), as a marker for myelinogenesis, was measured in different parts of the nervous system of dilute-lethal mutant mice (d1/d1). The activity in terms of micromoles of 2'-AMP formed per milligram of protein of homogenate per minute was found to be exceedingly reduced in the cerebrum, brain stem, and medulla oblongata, slightly reduced in the cerebellum and cervical spinal cord, but not reduced in the thoracic spinal cord and the optic and sciatic nerves. These results clearly indicate that dilute-lethal mutant mice show poor myelination in the cerebrum, brain stem, and medulla oblongata.