SUMMARY Chronic stress could trigger maladaptive changes associated with stress-related mental disorders, however, the underlying mechanisms remain elusive. In this study, we found that exposing juvenile male rats to repeated stress significantly impaired the temporal order recognition memory, a cognitive process controlled by prefrontal cortex (PFC). Concomitantly, significantly reduced AMPAR- and NMDAR-mediated synaptic transmission and glutamate receptor expression were found in PFC pyramidal neurons from repeatedly stressed animals. All these effects relied on activation of glucocorticoid receptors and the subsequent enhancement of ubiquitin/proteasome-mediated degradation of GluR1 and NR1 subunits, which was controlled by the E3 ubiquitin ligase Nedd4-1 and Fbx2, respectively. Inhibition of proteasomes or knockdown of Nedd4-1 and Fbx2 in PFC prevented the loss of glutamatergic responses and recognition memory in stressed animals. Our results suggest that repeated stress dampens PFC glutamatergic transmission by facilitating glutamate receptor turnover, which causes the detrimental effect on PFC-dependent cognitive processes.

The prefrontal cortex (PFC), a key brain region controlling cognition and emotion, is strongly influenced by stress. While chronic stress often produces detrimental effects on these measures, acute stress has been shown to enhance learning and memory, predominantly through the action of corticosteroid stress hormones. We used a combination of electrophysiological, biochemical, and behavioral approaches in an effort to identify the cellular targets of acute stress. We found that behavioral stressors in vivo cause a long-lasting potentiation of NMDAR-and AMPAR-mediated synaptic currents via glucocorticoid receptors (GRs) selectively in PFC pyramidal neurons. This effect is accompanied by increased surface expression of NMDAR and AMPAR subunits in acutely stressed animals. Furthermore, behavioral tests indicate that working memory, a key function relying on recurrent excitation within networks of PFC neurons, is enhanced by acute stress via a GR-dependent mechanism. These results have identified a form of long-term potentiation of synaptic transmission induced by natural stimuli in vivo, providing a potential molecular and cellular mechanism for the beneficial effects of acute stress on cognitive processes subserved by PFC.AMPA receptors ͉ corticosterone ͉ NMDA receptors

Corticosteroid stress hormones have a strong impact on the function of prefrontal cortex (PFC), a central region controlling cognition and emotion, though the underlying mechanisms are elusive. We found that behavioral stressor or short-term corticosterone treatment in vitro induces a delayed and sustained potentiation of the synaptic response and surface expression of NMDARs and AMPARs in PFC pyramidal neurons via a mechanism depending on the induction of serum- and glucocorticoid-inducible kinase (SGK) and the activation of Rab4, which mediates receptor recycling between early endosomes and the plasma membrane. Working memory, a key function relying on glutamatergic transmission in PFC, is enhanced in acutely stressed animals via a SGK-dependent mechanism. These results suggest that acute stress, by activating glucocorticoid receptors (GRs), increases the trafficking and function of NMDARs and AMPARs via SGK/Rab4 signaling, which leads to the potentiated synaptic transmission, thereby facilitating cognitive processes mediated by the PFC.

. Metformin was proposed to be a candidate for host-directed therapy for COVID-19. However, its efficacy remains to be validated. In this study, we compared the outcome of metformin users and nonusers in hospitalized COVID-19 patients with diabetes. Hospitalized diabetic patients with confirmed COVID-19 in the Tongji Hospital of Wuhan, China, from January 27, 2020 to March 24, 2020, were grouped into metformin and no-metformin groups according to the diabetic medications used. The demographics, characteristics, laboratory parameters, treatments, and clinical outcome in these patients were retrospectively assessed. A total of 283 patients (104 in the metformin and 179 in the no-metformin group) were included in this study. There were no significant differences between the two groups in gender, age, underlying diseases, clinical severity, and oxygen-support category at admission. The fasting blood glucose level of the metformin group was higher than that of the no-metformin group at admission and was under effective control in both groups after admission. Other laboratory parameters at admission and treatments after admission were not different between the two groups. The length of hospital stay did not differ between the two groups (21.0 days for metformin versus 19.5 days for no metformin, P = 0.74). However, in-hospital mortality was significantly lower in the metformin group (3/104 (2.9%) versus 22/179 (12.3%), P = 0.01). Antidiabetic treatment with metformin was associated with decreased mortality compared with diabetics not receiving metformin. This retrospective analysis suggests that metformin may offer benefits in patients with COVID-19 and that further study is indicated.

Parkinson disease (PD) is characterized by the specific degeneration of dopaminergic (DA) neurons in substantia nigra and has been linked to a variety of environmental and genetic factors. Rotenone, an environmental PD toxin, exhibited much greater toxicity to DA neurons in midbrain neuronal cultures than to non-DA neurons. The effect was significantly decreased by the microtubulestabilizing drug taxol and mimicked by microtubule-depolymerizing agents such as colchicine or nocodazole. Microtubule depolymerization disrupted vesicular transport along microtubules and caused the accumulation of dopamine vesicles in the soma. This led to increased oxidative stress due to oxidation of cytosolic dopamine leaked from vesicles. Inhibition of dopamine metabolism significantly reduced rotenone toxicity. Thus, our results suggest that microtubule depolymerization induced by PD toxins such as rotenone plays a key role in the selective death of dopaminergic neurons.At the cellular level Parkinson disease is characterized by the selective degeneration of dopaminergic neurons in substantia nigra. A variety of genetic and environmental factors contribute to such a specific loss. Long term epidemiological studies have indicated that exposure to agricultural pesticides represents a significant risk factor for Parkinson disease (1). It has been found recently that long term, systemic administration of rotenone, a natural substance widely used as a pesticide, produces selective degeneration of dopaminergic neurons and PD 2 -like locomotor symptoms in rats (2).Rotenone is a membrane-permeable compound that has two known molecular targets in the cell; it inhibits complex I in the mitochondrial respiratory chain (3) and depolymerizes microtubules (4, 5). The former activity has been studied extensively but could not fully explain the specificity of rotenone toxicity on DA neurons, as rotenone infusion uniformly inhibits complex I in all brain areas (2). Although the latter activity causes microtubule depolymerization in every type of cells, the consequence would be quite different. Nigral dopaminergic neurons send very long axons to striatum to control voluntary locomotor activity. Axonal transport of vesicles are mediated by microtubule-based motor proteins (6). Microtubule depolymerization would disrupt vesicular transport and cause the accumulation of vesicles in the soma. In the case of DA neurons, the cargo is dopamine, whose oxidation produces large quantities of reactive oxygen species and may trigger cell death (7). Other types of cells that do not have extensive processes or do not contain an oxidizable neurotransmitter (e.g. glutamatergic or GABAergic neurons) would be spared even though their microtubules are depolymerized by rotenone to a similar extent. In the present study we attempt to elucidate the role of microtubule depolymerization in the selective toxicity of rotenone on DA neurons. EXPERIMENTAL PROCEDURESAntibodies and Reagents-Rabbit anti-TH was from Affinity BioReagents (Golden, CO). Mouse anti-TH was from Pel-F...

A fundamental feature of Alzheimer disease (AD) is the accumulation of ␤-amyloid (A␤), a peptide generated from the amyloid precursor protein (APP). Emerging evidence suggests that soluble A␤ oligomers adversely affect synaptic function, which leads to cognitive failure associated with AD. The A␤-induced synaptic dysfunction has been attributed to the synaptic removal of ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors (AMPARs); however, it is unclear how A␤ induces the loss of AMPARs at the synapses. In this study we have examined the potential involvement of Ca 2؉ /calmodulindependent protein kinase II (CaMKII), a signaling molecule critical for AMPAR trafficking and function. We found that the synaptic pool of CaMKII was significantly decreased in cortical neurons from APP transgenic mice, and the density of CaMKII clusters at synapses was significantly reduced by A␤ oligomer treatment. In parallel, the surface expression of GluR1 subunit as well as AMPAR-mediated synaptic response and ionic current was selectively decreased in APP transgenic mice and A␤-treated cultures. Moreover, the reducing effect of A␤ on AMPAR current density was mimicked and occluded by knockdown of CaMKII and blocked by overexpression of CaMKII. These results suggest that the A␤-induced change in CaMKII subcellular distribution may underlie the removal of AMPARs from synaptic membrane by A␤.The accumulation of ␤-amyloid (A␤), 2 a peptide generated from the amyloid precursor protein (APP), is one of the hallmarks of Alzheimer disease (AD), a progressive neurodegenerative disorder (1, 2). Although it is still unclear how A␤ contributes to the etiology and pathogenesis of AD, emerging evidence suggests that A␤ causes "synaptic failure" before the formation of senile plaques and the occurrence of neuron death (3). Soluble oligomeric A␤ forms rather than amyloid plaques correlate with the severity of cognitive impairment in AD (4, 5). Application of naturally secreted A␤ oligomers adversely affects glutamatergic synaptic transmission and plasticity (6, 7). Neurons from transgenic mice overexpressing AD-linked mutant APP also show deficits in long term potentiation of synaptic transmission, a synaptic basis of learning and memory (8 -11). In addition, decreased expression of synaptic proteins and loss of synapses have been found with elevated A␤ levels (12-16). This A␤-induced synaptic dysfunction has been attributed to the synaptic removal of AMPA receptors (17-19). However, it is unclear how A␤ induces the loss of AMPARs at the synapses.The trafficking of AMPA receptors directly controls excitatory synaptic efficacy (20). Several mechanisms have been proposed to regulate the transport of AMPARs to and from the cell surface and lateral diffusion at synaptic and extrasynaptic sites (21), including PDZ domain-mediated interactions between channel and scaffolding proteins (22, 23), clathrin-dependent endocytosis (24, 25), and motor protein-based delivery along microtubule or actin cytoskeletons (26,27). CaMKII, a multifun...

Converging evidence suggests that females and males show different responses to stress; however, little is known about the mechanism underlying the sexually dimorphic effects of stress. In this study, we found that young female rats exposed to 1 week of repeated restraint stress show no negative effects on temporal order recognition memory (TORM), a cognitive process controlled by the prefrontal cortex (PFC), which was contrary to the impairment in TORM observed in stressed males. Concomitantly, normal glutamatergic transmission and glutamate receptor surface expression in PFC pyramidal neurons were found in repeatedly stressed females, in contrast to the significant reduction seen in stressed males. The detrimental effects of repeated stress on TORM and glutamate receptors were unmasked in stressed females when estrogen receptors were inhibited or knocked down in PFC, and were prevented in stressed males with the administration of estradiol. Blocking aromatase, the enzyme for the biosynthesis of estrogen, revealed the stress-induced glutamatergic deficits and memory impairment in females, and the level of aromatase was significantly higher in the PFC of females than in males. These results suggest that estrogen protects against the detrimental effects of repeated stress on glutamatergic transmission and PFC-dependent cognition, which may underlie the stress resilience of females.

Emerging evidence has suggested that glycogen synthase kinase 3 (GSK-3) is a key regulatory kinase involved in a plethora of processes in the nervous system, including neuronal development, mood stabilization, and neurodegeneration. However, the cellular mechanisms underlying the actions of GSK-3 remain to be identified. In this study, we examined the impact of GSK-3 on the N-methyl-D-aspartate (NMDA) receptor channel, a central player involved in cognitive and emotional processes. We found that application of various structurally different GSK-3 inhibitors caused a long-lasting reduction of NMDA receptor-mediated ionic and synaptic current in cortical pyramidal neurons. Cellular knockdown of GSK-3␤ in neuronal cultures with a small interfering RNA led to smaller NMDA receptor current and loss of its regulation by GSK-3 inhibitors. The NR2B subunit-containing NMDA receptor was the primary target of GSK-3, but the GSK-3 modulation of NMDAR current did not involve the motor protein kinesin superfamily member 17-based transport of NR2B-containing vesicles along microtubules. Combined electrophysiological, immunocytochemical, and biochemical evidence indicated that GSK-3 inhibitors induced the down-regulation of NMDAR current through increasing the Rab5-mediated and PSD-95-regulated NMDAR internalization in a clathrin/dynamin-dependent manner.