Received: 18 February 2002 Revised: 10 June 2002 Published online: 9 October 2002 © Springer-Verlag 2002 Abstract Introduction: There are controversies over the pattern of gli- al differentiation in spinal open neu- ral tube defect (ONTD) at the prena- tal stage. A surgical model of ONTD allows a more precise comparison of glial differentiation between the ONTD and control groups than chemical and genetic models. Mate- rials and methods: To investigate the influence of ONTDs on the patterns of glial differentiation, ONTDs were induced by surgery using Hamburger and Hamilton stage 18 or 19 chick embryos. The spinal cord tissues on postoperative days (POD) 5, 7, 10, and 14 were processed to observe as- trocytic, radial glial, and microglial differentiations by glial fibrillary ac- id protein (GFAP), vimentin and rici- nus communis agglutinin-I (RCA-I) stainings, respectively. Four embryos were assigned to subgroups of each POD. Control embryos (n=4) were staged but the neural tubes were not incised. Results: In the control group, GFAP positivity was shown faintly at the dorsal midline on em- bryonic day (E) 10 (corresponding to POD 7), in the ventral one-third of the white matter on E 13 and in the whole white matter on E 17. Embry- os with ONTDs showed earlier and stronger GFAP positivity from POD 7–14, especially at the dorsal surface and the adjacent gray matter. In the control group, vimentin staining demonstrated a positive reaction at the midline with positivity in a faint, radial pattern on E 8 and E 10. This had all disappeared by E 13 and 17. In embryos with ONTDs, vimentin positivity was enhanced and persist- ed from POD 5–14. These findings were prominent along the dorsal sur- face of ONTDs. No difference in RCA-I staining was found between the control and ONTD groups. Conclusion: The results reveal that ONTD promotes astrocytic differen- tiation and prolongs expression of radial glial fibers, which seems to be a reaction to the damage caused by exposure of the spinal cord tissue to amniotic fluid. Keywords Open neural tube defect · Surgical model · Astrocyte · Radial glial fiber · Microglia · Amniotic fluid Childs Nerv Syst (2002) 18:694–701 DOI 10.1007/s00381-002-0662-4 ORIGINAL PAPER Ki-Bum Sim You-Nam Chung Sa-Sun Cho Byung-Kyu Cho Martha Kim Dong Won Kim Yong Do Huh Kyu-Chang Wang Temporal and spatial patterns of glial differentiation in the surgically induced spinal open neural tube defect of chick embryos: astrocytic, radial glial and microglial differentiations Introduction Open neural tube defect (ONTD) is one of the represen- tative entities in the field of pediatric neurosurgery, and its prenatal management has already been intro- duced into practice. Studies of sheep fetuses with surgi- cally induced ONTDs and data from serial prenatal sonographic follow-up of human fetal meningomyelo- cele revealed a prenatal progressive neurological deteri- oration in spinal ONTDs at least in some patients [12, 15]. Understanding the mechanisms of prenatal injury and neurological deficits in ONTDs can be a basis for the further development of prenatal management strate- gies. K.-B. Sim Department of Neurosurgery, Cheju National University College of Medicine, Cheju, Korea Y.-N. Chung · B.-K. Cho · M. Kim K.-C. Wang ( ✉ ) Division of Pediatric Neurosurgery and Laboratory for Fetal Medicine Research, Clinical Research Institute, Seoul National University Hospital, 28 Yongon-dong, Chongno-gu, Seoul 110–744, Korea e-mail: kcwang@snu.ac.kr Tel.: +82-2-7603489 Fax: +82-2-7475130 S.-S. Cho Department of Anatomy, Seoul National University College of Medicine, Seoul, Korea D.W. Kim · Y.D. Huh Department of Neurosurgery, Kye-Myung University Dongsan Medical Center, Taegu, Korea