Chronic prenatal ethanol exposure alters hippocampal GABA A receptors and impairs spatial learning in the guinea pig

Abstract

Chronic prenatal ethanol exposure (CPEE) can injure the developing brain, and may lead to the fetal alcohol syndrome (FAS). Previous studies have demonstrated that CPEE upregulates γ-aminobutyric acid type A (GABA A) receptor expression in the cerebral cortex, and decreases functional synaptic plasticity in the hippocampus, in the adult guinea pig. This study tested the hypothesis that CPEE increases GABA A receptor expression in the hippocampus of guinea pig offspring that exhibit cognitive deficits in a hippocampal-dependent spatial learning task. Timed, pregnant guinea pigs were treated with ethanol (4 g/kg maternal body weight per day), isocaloric-sucrose/pair-feeding, or water throughout gestation. GABA A receptor subunit protein expression in the hippocampus was measured at two development ages: near-term fetus and young adult. In young adult guinea pig offspring, CPEE increased spontaneous locomotor activity in the open-field and impaired task acquisition in the Morris water maze. CPEE did not change GABA A receptor subunit protein expression in the near-term fetal hippocampus, but increased expression of the β2/3-subunit of the GABA A receptor in the hippocampus of young adult offspring. CPEE did not change either [ 3 H ]flunitrazepam binding or GABA potentiation of [ 3 H ]flunitrazepam binding, but decreased the efficacy of allopregnanolone potentiation of [ 3 H ]flunitrazepam binding, to hippocampal GABA A receptors in adult offspring. Correlational analysis revealed a relationship between increased spontaneous locomotor activity and growth restriction in the hippocampus induced by CPEE. Similarly, an inverse relationship was found between performance in the water maze and the efficacy of allopregnanolone potentiation of [ 3 H ]flunitrazepam binding in the hippocampus. These data suggest that alterations in hippocampal GABA A receptor expression and pharmacological properties contribute to hippocampal-related behavioral and cognitive deficits associated with CPEE.