A central concept in the field of learning and memory is that NMDARs are essential for synaptic plasticity and memory formation. Surprisingly then, multiple studies have found that behavioral experience can reduce or eliminate the contribution of these receptors to learning. The cellular mechanisms that mediate learning in the absence of NMDAR activation are currently unknown. To address this issue, we examined the contribution of Ca2+-permeable AMPARs to learning and plasticity in the hippocampus. Mutant mice were engineered with a conditional genetic deletion of GluR2 in the CA1 region of the hippocampus (GluR2-cKO mice). Electrophysiology experiments in these animals revealed a novel form of long-term potentiation (LTP) that was independent of NMDARs and mediated by GluR2-lacking Ca2+-permeable AMPARs. Behavioral analyses found that GluR2-cKO mice were impaired on multiple hippocampus-dependent learning tasks that required NMDAR activation. This suggests that AMPAR-mediated LTP interferes with NMDAR-dependent plasticity. In contrast, NMDAR-independent learning was normal in knockout mice and required the activation of Ca2+-permeable AMPARs. These results suggest that GluR2-lacking AMPARs play a functional and previously unidentified role in learning; they appear to mediate changes in synaptic strength that occur after plasticity has been established by NMDARs.

Vascular dementia ranks as the second leading cause of dementia in the United States. However, its underlying pathophysiological mechanism is not fully understood and no effective treatment is available. The purpose of the current study was to evaluate long-term cognitive deficits induced by transient middle cerebral artery occlusion (tMCAO) in rats and to investigate the underlying mechanism. Sprague-Dawley rats were subjected to tMCAO or sham surgery. Behavior tests for locomotor activity and cognitive function were conducted at 7 or 30 days after stroke. Hippocampal long term potentiation (LTP) and involvement of GABAergic neurotransmission were evaluated at 30 days after sham surgery or stroke. Immunohistochemistry and Western blot analyses were conducted to determine the effect of tMCAO on cell signaling in the hippocampus. Transient MCAO induced a progressive deficiency in spatial performance. At 30 days after stroke, no neuron loss or synaptic marker change in the hippocampus were observed. LTP in both sides of the hippocampus was reduced at 30 days after stroke. This LTP impairment was prevented by blocking GABAA receptors. In addition, ERK activity was significantly reduced in both sides of the hippocampus. In summary, we identified a progressive decline in spatial learning and memory after ischemic stroke that correlates with suppression of hippocampal LTP, elevation of GABAergic neurotransmission, and inhibition of ERK activation. Our results indicate that the attenuation of GABAergic activity or enhancement of ERK/MAPK activation in the hippocampus might be potential therapeutic approaches to prevent or attenuate cognitive impairment after ischemic stroke.

Under oxidative stress conditions, mitochondria are the major site for cellular production of reactive oxygen species (ROS) such as superoxide anion and H2O2 that can attack numerous mitochondrial proteins including dihydrolipoamide dehydrogenase (DLDH). While DLDH is known to be vulnerable to oxidative inactivation, the mechanisms have not been clearly elucidated. The present study was therefore designed to investigate the mechanisms of DLDH oxidative inactivation by mitochondrial reactive oxygen species (ROS). Mitochondria, isolated from rat brain, were incubated with mitochondrial respiratory substrates such as pyruvate/malate or succinate in the presence of electron transport chain inhibitors such as rotenone or antimycin A. This is followed by enzyme activity assay and gel-based proteomic analysis. The present study also examined whether ROS-induced DLDH oxidative inactivation could be reversed by reducing reagents such as DTT, cysteine, and glutathione. Results show that DLDH could only be inactivated by complex III- but not complex I-derived ROS; and the accompanying loss of activity due to the inactivation could be restored by cysteine and glutathione, indicating that DLDH oxidative inactivation by complex III-derived ROS was a reversible process. Further studies using catalase indicate that it was H2O2 instead of superoxide anion that was responsible for DLDH inactivation. Moreover, using sulfenic acid-specific labeling techniques in conjunction with two-dimensional Western blot analysis, we show that protein sulfenic acid formation (also known as sulfenation) was associated with the loss of DLDH enzymatic activity observed under our experimental conditions. Additionally, such oxidative modification was shown to be associated with preventing DLDH from further inactivation by the thiol-reactive reagent N-ethylmaleimide. Taken together, the present study provides insights into the mechanisms of DLDH oxidative inactivation by mitochondrial H2O2.

Strawberries contain a wide array of nutrients and phytochemicals including polyphenols such as anthocyanins, proanthocyanidins and ellagitannins. These polyphenols are absorbed and metabolized to various phenolic metabolites/conjugates in the body, which may play a role in disease risk reduction. In the present study, we investigated the metabolic fate of strawberry polyphenols after chronic (90 days) supplementation of freeze-dried strawberry (24 g d, equivalent to 2 cups of fresh strawberries) vs. control powder in 19 healthy older adults. Blood samples were collected at two time-points i.e., fasting (t = 0 h) and 2 h after the breakfast meal. On days 45 and 90 breakfast also included a control or strawberry drink consistent with their treatment randomization. A total of 21 polyphenolic metabolites were quantified in plasma consisting of 3 anthocyanins/metabolites, 3 urolithin metabolites and 15 phenolic acid metabolites. Among anthocyanins/metabolite, pelargonidin glucuronide (85.7 ± 9.0 nmol L, t = 2 h, day 90) was present in the highest concentration. Persistent concentrations of anthocyanins/metabolites, urolithins and some phenolic acids were observed in fasting (t = 0 h) plasma samples on day 45 and 90 after strawberry drink consumption suggesting a role of enteric, enterohepatic recycling or upregulation of gut microbial and/or human metabolism of these compounds. Our results suggest that strawberry polyphenols are absorbed and extensively metabolized, and can persist in the circulation.