Amniotic fluid cholinesterase of valproate-induced exencephaly in the mouse: an animal model for prenatal diagnosis of neural tube defects

Sodium valproate augments spontaneous neural tube defects and axial skeletal malformations in TO mouse fetuses [corrected]

The TO mouse exhibits a low incidence (3.65%) of spontaneous exencephaly at birth. The objectives of this study were to determine if sodium valproate (VPA) would augment this background frequency of exencephaly and to characterize its gross and histologic bases. Single doses of 200, 400, or 600 mg/kg of VPA were administered on one of gestation days (GD) 7 to 10 and fetuses were collected on GD 18. Significant augmentation of the background incidence of exencephaly was observed in the GD 7 and 8 treatment groups. Absence of the skull vault, hemorrhage, and degeneration of the exposed brain, polyhydramnios, and a female excess characterized the abnormality. Exencephalic embryos were markedly growth retarded. In addition to craniofacial and urogenital anomalies, severe axial skeletal malformations were found to be consistently associated with exencephaly. Morphometric evaluation of the alizarin red-stained skeleton confirmed significant skeletal growth inhibition. Histologic sections of GD 10 embryos revealed early onset of treatment-related growth retardation. Arrest of closure appeared to affect intermittent segments of the neural tube. The closure defect sometimes only involved the surface ectoderm of the dorsal midline. The unclosed neural tube was at times covered by a continuous layer of surface ectoderm. Cell death per se was not pronounced in the neuroepithelium. The mesenchyme was generally sparse and edema was obvious in embryos with partial closure. Growth inhibition of the optic and otic primordia was marked by pronounced cell death in these structures as well as in the otic and trigeminal ganglia and in the pharyngeal arch mesenchyme. Evidence for neural crest cell migration was also recorded. These data indicate that VPA interacts with genetic susceptibility, augments the frequency of exencephaly, and also induces other malformations in the TO mouse. The widespread malformations of the cranifacial structures are suggestive of the preferential effect of VPA on the neural crest or its derivatives.

Prenatal diagnosis of exencephaly

This paper presents a sonographic diagnosis of exencephaly made during the last trimester of gestation. The sonogram showed the absence of bones in the cranial vault together with the presence of a disorganized cerebral mass, with loss of its normal anatomy. Post-partum examination of the newborn confirmed the findings of the sonogram. We briefly review the characteristics of exencephaly, its aetiology, and its relationship to anencephaly.

Developmental toxicity of valproic acid

Valproic acid is a very effective anticonvulsant agent widely used in the management of various forms of epilepsy. Administration of the drug during pregnancy results in increased incidence of congenital abnormalities in both humans and experimental animals. In recent years, a significant number of research efforts have attempted to define the contributory role of valproic acid to the impairment of normal prenatal growth and development. The present report summarizes current knowledge that has emerged from clinical and research studies. The specific topics include: the placental transfer of valproic acid; the teratogenic potential; structure-teratogenicity and dose-response relationships; species and strain differences; biochemical changes evoked by the drug in the fetus.