NEUROANATOMICAL LOCALIZATION OF MYELIN BASIC-PROTEIN IN THE LATE 1ST AND EARLY 2ND TRIMESTER HUMAN FETAL SPINAL-CORD AND BRAIN-STEM

The temporal and spatial expression of myelin basic protein in the fir st and second trimester human foetal spinal cord and brainstem from 9 to 20 gestational weeks was determined by immunocytochemistry in secti ons of cervical, thoracic and lumbosacral levels from 41 human foetal spinal cords and ten brainstems. Myelin basic protein-positive oligode ndrocytes were observed peripheral to the ependyma at 9-10 gestational weeks. Oligodendrocytes expressing myelin basic protein were seen at 10-12 gestational weeks in the anterior and lateral funiculi. Myelin b asic protein was detected later in the posterior funiculi than in the anterolateral white matter and most spinal cord tracts could not be id entified by means of variation in myelin basic protein expression. Myl ein basic protein' was found in the midline of the brainstem at ten ge stational weeks and spread laterally during the second trimester. We c onclude that in the human foetal spinal cord, myelin basic protein is present by 10 gestational weeks in the anterolateral cervical spinal c ord and midline of the brainstem. It is expressed in a rostral-to-caud al and anterolateral-to-posterior manner in most tracts of the spinal cord. However, an exception to these findings is that the fasciculus g racilis, upon developing into a defined region, had more myelin basic protein-positive cells at the lumbar level than in more rostral region s. Definition of the kinetics of myelin basic protein expression in th e normal human foetal spinal cord provides a baseline for study of abe rrant myelination and demyelination.