AbstractBACKGROUNDA widely‐used antimycotic agent, bis‐triazole fluconazole (FLUCO), is able to produce abnormalities to the branchial apparatus (hypoplasia, agenesis, and fusion) in postimplantation rodent embryos cultured in vitro. The branchial apparatus is a complex and transient structure in vertebrate embryos and is essential for the development of the face skeleton. Branchial arch mesenchyme is formed by two different cellular populations: paraxial mesenchyme and ectomesenchyme, which originate from rhombencephalic neural crest cell (NCC) migration. We investigated the possible pathogenic pathways involved in FLUCO‐related branchial arch abnormalities. Perturbations in physiological apoptosis, cell proliferation, NCC migration and branchial mesenchyme induction have been considered.METHODSRat embryos (9.5‐day postcoitum; 1–3 somites) were exposed in vitro to 0 or 500 μM FLUCO. After 24, 36, or 48 hr of culture, embryos were examined for apoptosis (acridine orange method) and cell proliferation (BrdU incorporation and detection method). Rhombencephalic NCC migration was analyzed using immunostaining of NCC (using anti‐CRABP antibodies) and the extracellular matrix (using anti‐fibronectin antibodies). The differentiative capability of the branchial mesenchymes was investigated using anti‐endothelin and anti‐endothelin‐receptor antibodies.RESULTSDuring the whole culture period, no alterations in physiological apoptosis, cell proliferation, and mesenchymal cell induction were observed in FLUCO‐exposed embryos in comparison to controls. On the contrary, severe alterations in NCC migration pathways were observed in FLUCO‐exposed embryos.CONCLUSIONSThe findings suggest that FLUCO produces teratogenic effects by interfering with the cellular and molecular mechanisms that control NCC migration. Birth Defects Research (Part A) 67:116–124, 2003. © 2003 Wiley‐Liss, Inc.