Prenatal ethanol exposure during the last third of gestation in rat reduces hippocampal NMDA agonist binding site density in 45-day-old offspring

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The effect of ethanol exposure during different periods of prenatal or postnatal development on hippocampal N-methyl-D-aspartate (NMDA) receptor binding was studied in rat. Fetal rat pups were exposed to ethanol for different periods of time during gestation via maternal consumption of a 3.35% ethanol liquid diet. In a separate experiment, neonatal pups were fed 2.51 g ethanol/kg body weight/day from Postnatal Day (PD) 4 to PD 10 via intragastric feeding tube. These two ethanol administration paradigms produced average peak maternal and pup blood ethanol concentrations of 39 mg/dl and 57 mg/dl, respectively. At 45 days of age, offspring from each treatment group were sacrificed for measurements of hippocampal NMDA-sensitive [ 3H]-glutamate binding site density using in vitro radiohistochemical techniques. As observed previously, prenatal ethanol exposure throughout gestation resulted in NMDA-sensitive [ 3H]-glutamate binding site reductions in the apical dendritic field regions of dentate gyrus, hippocampal CA 1 and subiculum of dorsal hippocampal formation compared to the ad lib or pair-fed control groups. NMDA-sensitive [ 3H]-glutamate binding was not different than control in rats exposed to ethanol during the first half of gestation only. Prenatal ethanol exposure during the last half or the last third of gestation resulted in NMDA-sensitive [ 3H]-glutamate binding site reductions comparable to the binding site reductions observed in rats exposed to ethanol throughout gestation. Hippocampal NMDA-sensitive [ 3H]-glutamate binding site density in postnatal ethanol-exposed rats was not different than the suckling or gastrostomy control groups. These results suggest that the critical period of vulnerability to ethanol-induced reductions in hippocampal NMDA receptor binding occurs during the last third of gestation in rat, which, in terms of human hippocampal development, is a period of time roughly equivalent to the fifth and six months of human gestation.