Hypothermia: teratogenic and protective effects on the development of mouse embryos in vitro

Inhibitors of glycolytic metabolism affect neurulation-staged mouse conceptuses in vitro

In order to evaluate the apparent discordance between altered glucose metabolism and embryonic energy production, the effects of inhibitors of glucose utilization on morphological development and biochemical changes in mouse embryos in culture were evaluated. Day 9 ICR mouse conceptuses having 3-6 pairs of somites were prepared for culture as previously described. 2-Deoxyglucose (2DG) produced a concentration-dependent effect on development. A 25 microM 2DG concentration did not induce neural tube closure defects (NTDs) but 100 microM, 100% of embryos exhibited this defect. A 17% reduction in the rate of lactate production by the conceptus was produced by a 24-hr exposure period to 100 microM 2DG. Iodoacetate, which inhibits glyceraldehyde-3-phosphate dehydrogenase in adult tissues, produced high rates of NTDs at concentrations > or = 2.5 microM. Following a 24 hour exposure to iodoacetate, lactate production was inhibited at 10 and 25 microM. The effects of 2DG on embryonic ATP content were assessed to test the hypothesis that effects on glucose utilization would effect embryonic ATP content. Despite using 2DG concentrations that alter development and inhibit glycolysis, there were no effects on whole embryo or visceral yolk sac (VYS) ATP content. However, when the embryo was divided into regions, there was a specific reduction in ATP content in the head following a 24-hr exposure period. No effect of 2DG on head ATP content was produced after 12 hr of exposure. To determine if there were region specific differences in 2DG uptake and distribution that could account for the differential effects of 2DG on ATP content, 14C-2DG accumulation in different regions of the embryo and VYS was determined over the 24-hr culture period. The uptake of 2DG was dependent on the medium 2DG concentration and suggested a higher accumulation in regions with decreased ATP. However, when the uptake was monitored for a 1-hr period after a 24-hr exposure, there was no region specific differences in 2DG uptake. These studies further document the adverse developmental effects of inhibitors of glucose utilization during the early stage of neurulation. The biochemical mechanism for induction of these defects is unclear, but an effect on ATP content does not appear to be solely responsible for the dysmorphogenesis.

Glucose causes lengthening of the microvilli of the neural plate of the rat embryo and produces a helical pattern on their surface

Prominent microvilli have been observed on the surface of neural plates in the embryos of many species. Since glucose is the main source of energy for embryos before neural tube closure and the onset of vascular circulation, it was of interest to study the relationship between these microvilli and glucose utilization in the neural plate. By applying microdrops of amniotic fluid to chemstrips, which colorimetrically measure glucose by glucose oxidase reaction, we determined that day 10 rat amniotic fluid glucose level was 31.6 +/- 1.6 mg/dl. On day 10 and within about 20 min from removal of the decidual sites, no glucose was found in the amniotic fluid. By use of a scanning electron microscope, the microvilli of the day 10 neural plate were found to have a 10-fold increase in length during a 40-min exposure to Hanks' solution at 21-23 degrees C. Similarly exposed embryos in Hanks' without glucose did not have microvillus elongation. However, under whole embryo culture conditions at 38 degrees C no extension of the microvilli was found. In the closed neural tube of the day 10 embryo, the microvilli were stubby and did not elongate with glucose exposure. Similarly, day 11 and 14 embryos had short microvilli which did not elongate with direct exposure to glucose at 21-23 degrees C. The short microvilli on the surface of the closed neural tube on day 11, 14, and 16 were associated with low glucose concentrations in the neural tube fluids. By use of a field emission scanning electron microscope, the surfaces of the microvilli in the extended position were seen to be covered by a right-handed helical array of globular objects the size of large molecules. The findings support the hypothesis that microvillar length may modulate glucose uptake. Shortening is associated with low concentrations of glucose in closed neural tubes, and lengthening occurs at glucose exposures of 100 mg/dl.