Application of the exo utero surgery to the study on the development of the cerebral cortical

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In spite of the great advance of the gene technology in recent years, the mechanism of mammalian brain development is not fully known. One of the reasons is the difficulty in observing and manipulating mammalian embryos which develop in the mother's uterus. In the present study, some experimental manupilations were made to the embryonic mouse brain by using exo utero sugery to clarify the developmental mechanisms of the cerebral cortex. We have already studied the in vivo development of the rat cerebral cortex and obtained the data which indicate that molecular interactions between neural cell adhesion molecules, L1 and TAG-1, and brain-specific chondroitin sulfate proteoglycan (CSPG), neurocan and phosphacan, are involved in the pathway formation of the cerebral cortex (Fukuda et al., 1997). In the developing rat cerebral cortex, L1 and TAG-1 immunoreactions were specifically localized on thalamocortical axons and cortical efferent axons, respectively. L1-bearing thalamocortical axons preferentially travel in the subplate of the cortical anlage where neurocan, was specifically expressed. In contrast, axons immunoreactive for TAG-1 evaded the subplate and run in the intermediate zone where neurocan expression was less prominent. In addition, TAG-1-bearing axons extensively invaded regions expressing another type of CSPG,phosphacan. Although both TAG-1 and L1 have been reported to bind both neurocan and phosphacan in vitro, various pattern of interactions between neural cell adhesion molecules and CSPGs may play important roles in the pathway formation of the forebrain. Based on these observation, we made microinjection of an enzyme which degrades chondrotin sulfate, antibody ageinst L1 or antisense oligo DNA of TAG-1 into the lateral ventricle of E13 mouse embryos using exo utero surgery, and exmined the brain histologically. This system will be a useful tool to study the developmental mechanism of the mammalian brain.