Developmental Analysis of Chlorambucil‐Induced Occipital Blebs in Mice

Abstract

SUMMARY This study was designed to examine whether defects of the meningeal anlage and intracranial hydrodynamic overload are involved in the pathogenesis of secondary cranioschisis after the neural tube closure. Chlorambucil (CA) 3.0–4.0 mg/kg administered to pregnant mice on day 7.5 of gestation (E7.5) caused abnormal blebs at the occipital region of embryos on E13.5 in a dose‐dependent fashion compared with control. At blebs, the mesencephalic ventricle was dilated, particularly on the dorsal midline and posterior to the pineal invagination. Histology showed fewer mesenchymal cells and vessels, as well as thinner neuroepithelial tissue than in controls. Transmission electron microscopy revealed that the cytoplasm of mesenchymal cells in the bleb region contained abnormal electron‐dense deposits, whereas deposits or other subcellular abnormalities were not evident in either the neuroepithelium or the surface ectoderm of the affected region. We administered 3.5 mg/kg of CA on E7.5 and studied the embryonic development. Mesodermal hypoplasia appeared on E11.5, whereas blebs were initially recognized on E13.5. On E15.5 and E18.5, the meninges and calvaria were hypoplastic, although no apparent cranioschisis was evident. To examine whether increased intracranial hydrodynamic pressure plus defects in the anlage of the meninges and cranium induces secondary cranioschisis, we injected kaolin into the cerebral ventricle on E13.5 to induce hydrocephaly. These embryos developed exo utero and we examined the morphology on E18.5. Hydrocephaly was induced and the defects were more severe in the meninges and cranium than in embryos exposed to CA alone, although cranioschisis was not histologically confirmed. These results suggested that hypoplasia in the mesoderm during early organogenesis underlies later abnormalities of the meninges and cranium, which may be involved in the pathogenesis of certain types of cranioschisis.

Application of the mouse exo utero development system in the study of developmental biology and teratology

“…Sekimoto et al . (1997) investigated the relationship among occipital bleb, intracranial hydrodynamic pressure and cranioschisis in mouse embryos using the exo utero sequential observation.…”

Sequential observations of exencephaly and subsequent morphological changes by mouse exo utero development system: analysis of the mechanism of transformation from exencephaly to anencephaly

“…Exencephaly is the exposure of a malformed brain lacking the skull vault, which has been suggested to result from a neural tube closure defect (Geelen et al 1980;Putz and Morriss-Kay 1981;Smith and Huntington 1981;Morrissey and Mottet 1983;Tanaka et al 1990) or the reopening of a closed neural tube (Gardner 1973;Webster and Messerle 1980;Padmanabhan 1984Padmanabhan , 1991Tanaka et al 1991;Sekimoto et al 1997). Anencephaly has been suggested to develop from exencephaly (O'Rahilly and Müller 2001); however, there is little direct experimental evidence to support this.…”

“…The exo utero development system (Muneoka et al 1986;Hatta et al 1994;Sekimoto et al 1997;Zhang et al 1998Zhang et al , 1999 allows direct and sequential observations of midto late-gestation mouse embryos. In this study, we examined the transformation from exencephaly to anencephaly using this system.…”

Effects of Restrained Fetal Movement on the Development of the Rat Hip Joint

“…Next, we compared the development of the hip joint in fetuses that were operated to restrict the motion of the one side of hind limbs with that in controls. Since it was reported that the movement of the hind limb of rat fetuses was first observed at El6 (Narayanan et al, 1971) and we observed the beginning of the joint cavity formation on that day, we operated on the fetuses at E16.5 and let the fetuses further develop ex0 urero to just before term to observe the effects (Muneoka et al, 1986;Hatta et al, 1994aHatta et al, , 1994bSekimoto et al, 1997;Zhang et al, 1998).…”

“…In the present study, we studied the effects of fetal movement of the hind limb on the formation of the hip joint in rats, and in particular, the development of the joint cavity and FH during the prenatal period. We restricted movements of the hind limb of rat fetuses and observed the effects using a technique of exo utero development (Muneoka et al, 1986;Hatta et al, 1994aHatta et al, , 1994bSekimoto et al, 1997;Zhang et al, 1998). We tied the one-sided hind limb onto the embryonic membrane to restrict the range of motion at the hip joint and compared the development of the operated hip joint with that of the unoperated or sham-operated controls.…”