ABSTRACT
The fragile X mental retardation protein (FMRP) is an important regulator of protein translation, and a lack of FMRP expression leads to a cognitive disorder known as fragile X syndrome (FXS). Clinical symptoms characterizing FXS include learning impairments and heightened anxiety in response to stressful situations. Here, we report that, in response to acute stress, mice lacking FMRP show a faster elevation of corticosterone and a more immediate impairment in N-methyl-d-aspartate receptor (NMDAR) dependent long-term potentiation (LTP) in the dentate gyrus (DG). These stress-induced LTP impairments were rescued by administering the glucocorticoid receptor (GR) antagonist RU38486. Administration of RU38486 also enhanced LTP in Fmr1(-/y) mice in the absence of acute stress to wild-type levels, and this enhancement was blocked by application of the NMDAR antagonist 2-amino-5-phosphonopentanoic acid. These results suggest that a loss of FMPR results in enhanced GR signaling that may adversely affect NMDAR dependent synaptic plasticity in the DG.
Subject(s)
Adrenal Cortex Hormones/blood , Dentate Gyrus/metabolism , Fragile X Mental Retardation Protein/metabolism , Neuronal Plasticity/genetics , Signal Transduction/genetics , Animals , Electric Stimulation , Excitatory Amino Acid Antagonists/pharmacology , Excitatory Postsynaptic Potentials/drug effects , Excitatory Postsynaptic Potentials/genetics , Fragile X Mental Retardation Protein/genetics , Hormone Antagonists/therapeutic use , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mifepristone/therapeutic use , Neuronal Plasticity/drug effects , Patch-Clamp Techniques , Restraint, Physical/adverse effects , Signal Transduction/drug effects , Stress, Psychological/drug therapy , Stress, Psychological/etiology , Time Factors , Valine/analogs & derivatives , Valine/pharmacologyABSTRACT
AIMS: Epidemiological findings demonstrated that increased plasma cholesterol levels are frequently observed in depressive patients. In this regard, there is enhancing evidence that hypercholesterolemia is associated with impairment of brain function. Recently, we demonstrated that low-density lipoprotein receptor knockout (LDLr(-/-)) mice- a widely used rodent model of familial hypercholesterolemia - exhibited memory deficits and cortico-cerebral mitochondrial dysfunction. In this study, we aimed to assess the hypercholesterolemic mice in predictive tasks for depressive-like behavior. METHODS: Adult wild type C57BL/6 and LDLr (-/-) mice were evaluated in two tests for depressive like behavior, the splash test and forced swimming test. In addition, the activity of monoamine oxidase isoforms and the mRNA levels of hemeoxygenase-1 were assessed in the hippocampus and cerebral cortex of C57BL/6 and LDLr (-/-) mice. Finally, the blood-brain-barrier (BBB) permeability was investigated using the AQP-4 immunofluorescence staining in the mice hippocampus. RESULTS: The LDLr (-/-) mice showed a significant reduction in the grooming time in the splash test and increased immobility time in the forced swimming test, and both parameters were reversed by fluoxetine antidepressant treatment (10mg/kg, 7 days, o.g.). Interestingly, the depressive like behavior of LDLr (-/-) mice was associated with increased activity of monoamine oxidase A, decreased hemeoxygenase-1 mRNA levels and increase of BBB permeability in the hippocampus. CONCLUSIONS: Overall, these data provide new evidence that hypercholesterolemia could trigger brain alterations involved in depressive disorders.
