PATTERNS OF GLIAL DEVELOPMENT IN THE HUMAN FETAL SPINAL-CORD DURING THE LATE FIRST AND 2ND TRIMESTER

Although the presence of radial glia, astrocytes, oligodendrocytes and microglia has been reported in the human foetal spinal cord by ten ge stational weeks, neuroanatomic studies employing molecular probes that describe the interrelated development of these cells from the late fi rst trimester through the late second trimester are few. In this study , immunocytochemical methods using antibodies to vimentin and glial fi brillary acidic protein were used to identify radial glia and/or astro cytes. An antibody to myelin basic protein was used for oligodendrocyt es and myelin; and, an antibody to phosphorylated high and medium mole cular weight neurofilaments identified axons. Lectin histochemistry us ing Ricinus communis agglutinin-I was employed to identify microglia. Vibratome sections from 35 human foetal spinal cord ranging in age fro m 9-20 gestation weeks were studied. By 12 gestational weeks, vimentin -positive radial glia were present at all three levels of the spinal c ord. Their processes were easily identified in the dorsal two-thirds o f cord sections, and reaction product for vimentin was more intense at cervical and thoracic levels than lumbosacral sections. By 15 gestati onal weeks, vimentin-positive processes were radially arranged in the white matter. At this time, glial fibrillary acidic protein-positive a strocytes were more obvious in both the anterior and anterolateral fun iculi than in the dorsal funiculus, and the same rostral to caudal gra dient was seen for glial fibrillary acidic protein as it was for vimen tin. Myelin basic protein expression followed similar temporal and spa tial patterns. Ricinus communis agglutinin-I labelling revealed more m icroglia in the white matter than in grey matter throughout the spinal cord from 10-20 gestational weeks. By 20 gestational weeks, the gradi ents of glial fibrillary acidic protein and vimentin expression were m ore difficult to discern. White matter contained more microglia than g rey matter. These results suggest that astrocytes as well as oligodend rocytes follow anterior-to-posterior and rostral-to-caudal development al patterns in the human foetus during middle trimester development.