Introduction: Animal studies modeling fetal alcohol syndrome have demonstrated that developmental exposure to alcohol is associated with decreased brain weight and significant neuronal loss in multiple regions of the developing brain. Our previous data suggest that the Fas/Apo [apoptosis]-1 receptor is transiently expressed in the developing cerebral cortex during the peak period of naturally occurring apoptotic cell death and maximum sensitivity to alcohol. Therefore, we hypothesized that ethanol increases the expression of suicide receptors such as Fas/Apo-1 in the developing fetal cerebral cortex and leads to an upregulation or extension of the normal period of apoptosis and consequent disorganization of the neural circuitry.
Methods: Ethanol was administered in one of four doses (120, 320, 630, and 950 mg/dl) to organotypic explant cultures of the developing cerebral cortex established from postnatal day 2 rats and maintained for 6 days in vitro. The number of cells expressing Fas/Apo-1 receptor mRNA was counted. Apoptosis was measured by the use of two independent assays; a cell death enzyme-linked immunosorbent assay for DNA fragmentation and flow cytometric analysis of Annexin-V binding to phosphatidylserine externalized to the outer leaflet of the plasma membrane. Necrosis was also estimated by two independent measures, the amount of lactate dehydrogenase released into culture medium and flow cytometric analysis of cells that were positive for both Annexin-V and propidium iodide.
Results: A significantly larger number of developing cortical cells expressed Fas/Apo-1 mRNA at the lower doses (120 and 320 mg/dl) than at the higher doses (630 and 950 mg/dl). Furthermore, ethanol induced apoptosis in a dose-related manner, with peak apoptosis observed at a dose of 630 mg/dl in the case of DNA fragmentation and at 630 and 950 mg/dl in the case of phosphatidylserine translocation to the outer leaflet of the plasma membrane. Ethanol did not induce necrosis at any of the administered doses of ethanol.
Conclusions: Our data suggest that ethanol induces a susceptibility to apoptotic signals at low doses by upregulating the expression of mRNAs for cytotoxic receptors such as Fas/Apo-1 in the developing cerebral cortex. However, ethanol itself specifically induces apoptosis in the developing cerebral cortex only at higher doses.