A quantitative analysis of rat central nervous system myelination using the immunohistochemical method for MBP

The temporal order of the myelination of the nervous pathways in 0-42-day-old Wistar rats was quantitatively analyzed using immunohistochemistry with anti-myelin basic protein (MBP) antibody. Immunohistochemistry was performed on paraffin-embedded tissue according to the standard ABC technique. For the objective evaluation of myelination, we converted the level stained with the immunohistochemical method into continuous numbers of 0-256 giving the intensity of myelination, using an image analyzing system. We analyzed nine nervous pathways: corpus callosum, optic tract, internal capsule, spinal tract of trigeminal nerve, inferior cerebellar peduncle, cerebellar white matter, pyramidal tract, medial longitudinal fasciculus, and cuneate fasciculus. The onset of the myelination of the spinal tract of the trigeminal nerve, inferior cerebellar peduncle, medial longitudinal fasciculus and cuneate fasciculus was day 7 (postnatal). That of the corpus callosum, optic tract, internal capsule and cerebellar white matter was day 14, and that of the pyramidal tract was day 21. The time required to reach the level of myelination of day 42 was day 21 for the spinal tract of the trigeminal nerve and the inferior cerebellar peduncle, day 28 for the internal capsule, day 35 for the corpus callosum, optic tract, cerebellar white matter and pyramidal tract, and day 42 for the medial longitudinal fasciculus. Our method using immunohistochemistry with anti-MBP antibody provided a highly sensitive and objective criterion for judging precisely the time and the progress of myelination in each nervous pathway and compare one nervous pathway with another.