The effects of lithium on neurulation stage mouse embryos.

The aim of this study was to evaluate the maternal toxicity and teratogenicity of lithium following intraperitoneal injection (i.p.) with lithium carbonate (Li2CO3) in pregnant CD-1 mice at the developmental stage of neurulation (E8; day of vaginal plug, E0). Light (LM) and electron (TEM) microscopic studies were also done to document the tissue and cellular changes occurring in embryonic tissues during the 48 h following treatment with 300 mg/kg body wt. Li2CO3. Controls were untreated or given equimolar amounts of NaCl or Na2CO3. A pharmacokinetic study showed that lithium was rapidly absorbed from the peritoneal cavity after the above-stated dose, achieved peak serum levels of 9.8 mmol/l within 1 h, had a half-life in the blood of 5 h and was completely cleared by 16 to 24 h after injection. Doses of Li2CO3 > 300 mg/kg body wt. were toxic to adult CD-1 mice. The latter dose had no detectable maternal toxicity but caused a 19% resorption rate and 2% incidence of open cranial neural tube defect in gestations terminated on E18. The malformation and resorption rates in gestations terminated on E11, E12 and E14 were not significantly different from those of E18. A strong litter effect was seen both for the resorption and malformation rates at all stages examined. At 3 h after treatment cell death became evident in the neuroepithelium. Cells continued to die for approximately 17 h and all necrotic debris had been cleared by 48 h. Also at 3 h after treatment small densely stained inclusions began to appear in mesodermal cells. TEM showed these to be non-membrane bound with an irregular shape and variable size; the lack of staining for acid phosphatase indicated a non-lysosomal structure; the ultrastructural features suggested a lipoid basis. At 24 h after treatment vascular ruptures and surface ectodermal ruptures were seen in the cranial mesoderm. These ruptures with extravascated blood were also seen at 48 h after treatment. A litter effect was also noted with respect to the tissue and cellular changes. These experiments suggest that the developing vascular system may be a target for lithium. In addition, the possibility is discussed that lithium induced cell death in the neuroepithelium may lead to neural tube defects.