Prenatal ethanol exposure has sex-specific effects on hippocampal long-term potentiation

Alcohol consumption during pregnancy is deleterious to the developing brain of the fetus and leads to persistent deficits in adulthood. Long-term potentiation (LTP) is a biological model for learning and memory processes and previous evidence has shown that prenatal ethanol exposure (PNEE) affects LTP in a sex specific manner during adolescence. The objective of this study was to determine if there are sex specific differences in adult animals and to elucidate the underlying molecular mechanisms that contribute to these differences. Pregnant Sprague-Dawley dams were assigned to either; liquid ethanol, pair-fed or standard chow diet. In vivo electrophysiology was performed in the hippocampal dentate gyrus (DG) of adult offspring. LTP was induced by administering 400 Hz stimuli. Western blot analysis for glutamine synthetase (GS) and glutamate decarboxylase from tissue of the DG indicated that GS expression was increased following PNEE. Surprisingly, adult females did not show any deficit in N-methyl-D-aspartate (NMDA)-dependent LTP after PNEE. In contrast, males showed a 40% reduction in LTP. It was indicated that glutamine synthetase expression was increased in PNEE females, suggesting that altered excitatory neurotransmitter replenishment may serve as a compensatory mechanism. Ovariectomizing females did not influence LTP in control or PNEE animals, suggesting that circulating estradiol levels do not play a major role in maintaining LTP levels in PNEE females. These results demonstrate the sexually dimorphic effects of PNEE on the ability for the adult brain to elicit LTP in the DG. The mechanisms for these effects are not fully understood, but an increase in glutamine synthetase in females may underlie this phenomenon.

Rescue of NMDAR-dependent synaptic plasticity in Fmr1 knock-out mice

Fragile X Syndrome (FXS) is the most common form of inherited intellectual disability and results from a loss of Fragile X mental retardation protein (FMRP). FMRP is important for mRNA shuttling and translational control and binds to proteins important for synaptic plasticity. Like many developmental disorders, FXS is associated with alterations in synaptic plasticity that may impair learning and memory processes in the brain. However, it remains unclear whether FMRP plays a ubiquitous role in synaptic plasticity in all brain regions. We report that a loss of FMRP leads to impairments in N-methyl-D-aspartate receptor (NMDAR)-dependent synaptic plasticity in the dentate gyrus (DG), but not in the cornu ammonis area 1 (CA1) subregion of the hippocampus of adult mice. DG-specific deficits are accompanied by a significant reduction in NMDAR GluN1, GluN2A, and GluN2B subunit levels and reduced serine 831 GluA1 phosphorylation specifically in this region. Importantly, we demonstrate that treatment with NMDAR co-agonists (glycine or D-serine) independently rescue impairments in NMDAR-dependent synaptic plasticity in the DG of the Fragile X mental retardation 1 (Fmr1) knockout mouse. These findings implicate the NMDAR in the pathophysiology of FXS and suggest that indirect agonists of the NMDAR may be a successful therapeutic intervention in FXS.