ABSTRACT
The N-methyl-D-aspartate receptor is a critical molecule for synaptic plasticity and cognitive function. Impaired synaptic plasticity is thought to contribute to the cognitive impairment associated with Alzheimer's disease (AD). However, the neuropathophysiological alterations of N-methyl-D-aspartate receptor (NMDAR) function and synaptic plasticity in hippocampal CA1 in transgenic rodent models of AD are still unclear. In the present study, APP/PS1 mice were utilized as a transgenic model of AD, which exhibited progressive cognitive impairment including defective working memory, recognition memory, and spatial memory starting at 6 months of age and more severe by 8 months of age. We found an impaired long-term potentiation (LTP) and reduced NMDAR-mediated spontaneous excitatory postsynaptic currents (sEPSCs) in the hippocampal CA1 of APP/PS1 mice with 8 months of age. Golgi staining revealed that dendrites of pyramidal neurons had shorter length, fewer intersections, and lower spine density in APP/PS1 mice compared to control mice. Further, the reduced expression levels of NMDAR subunits, PSD95 and SNAP25 were observed in the hippocampus of APP/PS1 mice. These results suggest that NMDAR dysfunction, impaired synaptic plasticity, and disrupted neuronal morphology constitute an important part of the neuropathophysiological alterations associated with cognitive impairment in APP/PS1 mice.
ABSTRACT
Juvenile social isolation (SI) and neglect have a negative impact on neurodevelopment persistently, which is associated with cognitive dysfunction in neurodevelopmental disorders. Given the critical role of metabotropic glutamate receptors (mGluRs) in synaptic homeostasis of the prefrontal cortex (PFC), pharmacological intervention on mGluRs has been attempted in order to improve cognitive dysfunction in animal models of neurodevelopmental disorder, as well as in clinical trials. Here we examined the effects of the mGluR2/3 antagonist LY341495 on prefrontal synaptic transmission, spatial working memory, and recognition memory in adult C57BL/6J mice that experienced juvenile SI. We found that SI-reared mice exhibited working memory impairment and decreased excitatory presynaptic release probability of pyramidal neurons in the medial PFC compared with group-reared mice. The positive effect of LY341495 on excitatory synaptic transmission in SI-reared mice was more prominent than the effect in group-reared mice. A single treatment with mGluR2/3 antagonist LY341495 significantly improved the performance of SI-reared mice in the Y-maze test but not in the novel object recognition (NOR) test, while repeated treatments were effective in both tasks. These findings suggest that enhancing glutamatergic transmission via inhibition of mGluR2/3 signaling might represent a promising strategy for improving cognitive function in neurodevelopmental disorders.
