Diazepam‐induced neural tube closure defects in explanted early chick embryos

Abstract

The effects of diazepam on the development of explanted stage 4 chick embryos were investigated. Diazepam, at 10-120 micrograms/ml, preferentially inhibited closure of the neural tube. This effect was reversible. Concentrations of 150-200 micrograms/ml inhibited not only neural tube closure but also blastodermal expansion, somite formation, and heart development in 52% of the embryos. Concentrations above 200 micrograms/ml were highly embryotoxic. Electron microscopy of affected neuroepithelial cells revealed that 1) apical surfaces were much smoother than usual and 2) apical filament bundles, which are generally thought to provide motive forces for uplifting of neural folds, were not well organized and often lacked alternating dark and light areas along their length. These findings and the fact that changes in cell surface topography reflect the contractile activities of underlying filament bundles suggest that the observed "smoothing" effect on apical cell surfaces and neural tube closure defects are due, at least in part, to the impaired ability of these filament bundles to contract.

Neural tube formation in the mouse: a morphometric and computerized three-dimensional reconstruction study of the relationship between apical constriction of neuroepithelial cells and the shape of the neuroepithelium

“…In addition, numerous studies on other chemical agents (e.g., local anesthetics, calcium agonists and antagonists, and calmodulin inhibitors) that interfere with microfilament-dependent cellular processes have been found to inhibit apical constriction of neuroepithelial cells and neural tube closure (Moran 1976;Moran and Rice 1976;Lee et al 1978;Lee and Nagele 1979;O'Shea and Kaufman 1980;Morriss-Kay 1981;Nagele et al 1981;Morriss-Kay and Tuckett 1985;Nagele 1985a-c, 1986). We are currently studying the ways in which forces derived from microfilament-mediated, apical constriction of neuroepithelial cells are deployed during sequential phases of neural tube formation in the future forebrain, midbrain, hindbrain, and spinal cord of the mouse embryo.…”

A morphometric and computer‐assisted three‐dimensional reconstruction study of neural tube formation in chick embryos

“…As noted above, the contractile activity of apical microfilament bundles is thought to cause apical narrowing (constriction) of NE cells, which, in turn, buckles their lumina1 surfaces into numerous folds. In support of this idea, numerous studies (e.g., Karfunkel, 1972;Linville and Shepard, 1972;Messier and Auclair, 1974;Lee and Kalmus, 1976;Moran and Rice, 1976;Lee et al, 1978;Lee and Nagele, 1979;Morris-Kay, 1981;Nagele et al, 1981;Lee and Nagele, 1985a;Morriss-Kay and Tuckett, 1985;Lee and Nagele, 1986) have shown that chemical agents (e.g., cytochalasins, local anesthetics, calcium agonist and antagonists, and calmodulin inhibitors), known to interfere with microfilament-dependent processes, inhibit apical constriction and NT closure, and have a "smoothing and broadening" effect on the apical ends of NE cells. During NT formation, NE cells at different locations within the wall of the forming NT exhibit considerable, regionspecific variations in the degree of apical constriction and surface folding.…”

In vitro screening for anticonvulsant‐induced teratogenesis in neural primary cultures and cell lines

“…The compounds were selected to provide examples of each of the major anticonvulsant classes. Valproate and diazepam have been specifically associated with neural tube defects, 20,27,48 whereas the other compounds have not. Diazepam-induced neural tube closure defects have been reported in explanted chick embryos.…”

“…Diazepam-induced neural tube closure defects have been reported in explanted chick embryos. 27 In the mouse and hamster diazepam, at high concentrations, has been shown to induce exencephaly.48 neural tube defects. '…”