Developmental change of the nestin-immunoreactive midline raphe glial structure in human brainstem and spinal cord

To elucidate the development of the midline raphe glial structure (MRGS) in human brainstem and spinal cord, immunohistochemistry was carried out in 10 developmentally normal brains (age range, 11 weeks postconception to 6 months) using antibodies to nestin and glial fibrillary acidic protein (GFAP). Nestin expression was most extensive in the youngest fetus (11 weeks postconceptional age, PCA), which showed strong immunoreactivity in radial glial fibers in the midline raphe and paramedian areas of brainstem and spinal cord. Nestin-immunoreactive radial glial fibers in the midline raphe gradually decreased in length and intensity, losing contact with the pial surface 20-24 weeks PCA. Radial glial cells in midbrain transformed into subependymal cells at 30 weeks PCA. Some fragments of radial fibers in brainstem and spinal cord could still be detected up to 30 weeks PCA. Weak GFAP immunoreactivity in the midline raphe was found in radial fibers in the dorsal midline of the midbrain and cervical spinal cord at 30 and 38 weeks PCA. This change of nestin positivity was thought to be due to the process remodeling the MRGS, not to the intracellular distribution and any identifiable clinical factors in the stillbirths. This irregularity in the appearance of the MRGS supports its proposed role as a guide for cell migration, a potential source of new astrocytes, and a barrier to aberrant decussation of growing axons.