Hippocampal GluA2 and GluA4 protein but not corresponding mRNA and promoter methylation levels are modulated at retrieval in spatial learning of the rat

Abstract

AMPA receptors mediate most fast excitatory synaptic transmission in the brain. Highly dynamic AMPA receptors are subjected to trafficking, recycling, and/or degradation and replacement. Changes in AMPA receptor abundance is an important mechanism involved in learning and memory formation. Results obtained with the Morris water maze (MWM), a paradigm for testing spatial memory in rodent, correlate with hippocampal synaptic plasticity and NMDA function. Different phases of spatial learning like acquisition and retrieval involve AMPA receptors. Long-term memory formation requires dynamic changes in gene transcription and protein synthesis. It is, however, not known so far if epigenetic marks such as DNA methylation and mRNA levels participate in regulation of AMPA receptors in hippocampus during memory retrieval. In the present study, rats were trained or untrained in the MWM. Steady state levels of hippocampal GluA1-4 mRNA were determined by RT-PCR and promoter methylation levels of GluA1-4 by in-house developed bisulfite pyrosequencing methods. GluA1-4 protein levels were determined in parallel in a membrane fraction by SDS-PAGE followed by Western blotting. Our results indicate that changes of hippocampal membrane AMPA receptors were modulated at the protein level, while no changes were observed at the mRNA and at the promoter methylation level of hippocampal GluA1-4. Training in the MWM at retrieval may, therefore, involve GluA2 and GluA4 subunits that may be regulated by protein stability or trafficking as protein determinations were carried out in a hippocampal membrane fraction.

Inhibiting RIP1 Improves Chronic Stress-Induced Cognitive Impairments in D-Galactose-Induced Aging Mice

“…Previous studies have shown that increasing hippocampal neurogenesis can improve pattern separation in object recognition ( Sahay et al, 2011 ). Penn et al (2017) found that GluA2 plays an important role in the maintenance of long-term potentiation and retrieval in spatial learning ( Rossner et al, 2017 ). These results suggested that the rescue of neurogenesis and GluA2 expression were the potential mechanisms underlying the protective effect of necrostatin-1 in stressed artificial aging mice.…”

Modulation of AMPA Receptors by Nitric Oxide in Nerve Cells

“…AMPA receptors, as major elements of excitatory transmission in the mammalian central nervous system, are also strongly involved in memory modifications and maintenance. AMPA receptors' trafficking is involved in memory expression, and regulation of the trafficking is very important for memory storage and modifications [156][157][158]. Blockade of AMPA receptors' endocytosis in the postsynapse leads to the preservation of memory [62].…”