HYPERGLYCEMIA DELAYS ROSTRAL INITIATION SITES DURING NEURAL-TUBE CLOSURE

Neural tube defects contribute greatly to perinatal loss, physical han dicap, mental retardation and other developmental defects, yet the mec hanisms through which they occur are poorly understood. One hindrance to the study of these defects at the cellular and molecular levels is the low frequency with which they arise in susceptible animals. The pr esent study utilizes a culture system for the study of rodent exenceph aly, an animal model of human anencephaly, in which a high frequency o f affected animals are obtained by culture in hyperglycemic rat serum. Rat embryos were dissected at day 9.5 from timed-pregnant Sprague-Daw ley dams and cultured under standard conditions developed by New [Biol . Rev. (1978) 53, 81-122]. Embryos cultured under elevated glucose con ditions are able to close the caudal neural tube with the failure of n eural tube closure limited to the rostral neuralepithelium. In this re port we present the novel finding that, although at the end of culture frequently only the hindbrain region remains open, the normal sequenc e of events expected during rostral closure anterior to the hindbrain is markedly delayed. In embryos cultured in hyperglycemic serum, both rostral initiation sites II and III are significantly delayed. The deg ree of delay increases with increasing glucose concentration in the cu lture medium. These studies support the use of this defined in vitro m odel of anencephaly for studies of the molecular and cellular bases un derlying the failure of hindbrain closure and demonstrate that suffici ent numbers of affected animals can be produced to obtain significant results. The similarity of our findings with hyperglycemia-induced exe ncephaly to studies in mouse strains that are genetically susceptible to anencephaly suggest that the mechanisms underlying these different routes to failure of neural tube closure share common precursor events .