Intermittent Hypoxia causes targeted disruption to NMDA receptor dependent synaptic plasticity in area CA1 of the...

Changed NMDA receptor (NMDAr) physiology is implicated with cognitive deficit resulting from conditions ranging from normal aging to neurological disease. Using intermittent hypoxia (IH) to experimentally model untreated sleep apnea, a clinical condition whose comorbidities include neurocognitive impairment, we recently demonstrated that IH causes a pro-oxidant condition that contributes to deficits in spatial memory and in NMDAr-dependent long-term potentiation (LTP). However, the impact of IH on additional forms of synaptic plasticity remains ill-defined. Here we show that IH prevents the induction of NMDAr-dependent LTP and long-term depression (LTD) in hippocampal brain slices from mice exposed to ten days of IH (IH₁₀) yet spares NMDAr-independent forms of synaptic plasticity. Deficits in synaptic plasticity were accompanied by a reduction in hippocampal GluN1 expression. Acute manipulation of redox state using the reducing agent, Dithiothreitol (DTT) stimulated the NMDAr-dependent fEPSP following IH₁₀. However, acute use of either DTT or MnTMPyP did not restore NMDAr-dependent synaptic plasticity after IH₁₀ or prevent the IH-dependent reduction in GluN1, the obligatory subunit of the NMDAr. In contrast, MnTMPyP during IH₁₀ (10-MnTMPyP), prevented the suppressive effects of IH on both NMDAr-dependent synaptic plasticity and GluN1 expression. These findings indicate that while the IH-dependent pro-oxidant state causes reversible oxidative neuromodulation of NMDAr activity, acute manipulation of redox state is ineffective in rescuing two key effects of IH related to the NMDAr within the hippocampus. These IH-dependent changes associated with the NMDAr may be a primary avenue by which IH enhances the vulnerability to impaired learning and memory when sleep apnea is left untreated in normal aging and in disease.