Time‐lapse photographic study of neural tube closure defects caused by xylocaine in the chick

Sequential changes in the morphology of early chick embryos were, for the first time, photographically recorded. Embryos were explanted at stage 8 (four‐somite) or 9– (six‐somite) of development using New's technique and grown in nutrient medium (thin albumen) with or without a teratologic dose (200 μg/ml) of xylocaine. They were photographed using a Nikon Diaphot inverted microscope equipped with both phase‐contrast optics and photomicro‐graphic accessories maintained in an incubator. It was found, among other things, that a characteristic neural tube closure defect often seen in the midbrain and anterior portion of the hindbrain of xylocaine (200 μg/ml)‐treated chick embryos was a consequence of failure of the neural tube to withstand the tension generated by the rapidly expanding cephalic region, which occurred, regardless of the stage at explantation, when corresponding control embryos had advanced to stage 10+ (11‐somite) of development.