From acquisition to consolidation: on the role of brain-derived neurotrophic factor signaling in hippocampal-dependent learning

The brain-derived neurotrophic factor Val66Met genotype does not influence the grey or white matter structures underlying recognition memory

A single nucleotide polymorphism (SNP) in the gene coding for brain-derived neurotrophic factor (BDNF) has previously been associated with a reduction in recognition memory performance. While previous findings have highlighted that this SNP contributes to recognition memory, little is known about its influence on subprocesses of recognition, familiarity and recollection. Previous research has reported reduced hippocampal volume and decreased fractional anisotropy in carriers of the Met allele across a range of white matter tracts, including those networks that may support recognition memory. Here, in a sample of 61 healthy young adults, we used a source memory task to measure accuracy on each recognition subprocess, in order to determine whether the Val66Met SNP (rs6265) influences these equally. Additionally, we compared grey matter volume between these groups for structures that underpin familiarity and recollection separately. Finally, we used probabilistic tractography to reconstruct tracts that subserve each of these two recognition systems. Behaviourally, we found group differences on the familiarity measure, but not on recollection. However, we did not find any group difference on grey- or white-matter structures. Together, these results suggest a functional influence of the Val66Met SNP that is independent of coarse structural changes, and nuance previous research highlighting the relationship between BDNF, brain structure, and behaviour.

NLRP3 inflammasome inhibition with MCC950 improves diabetes-mediated cognitive impairment and vasoneuronal remodeling after ischemia

Diabetes increases the risk and worsens the progression of cognitive impairment via the greater occurrence of small vessel disease and stroke. Yet, the underlying mechanisms are not fully understood. It is now accepted that cardiovascular health is critical for brain health and any neurorestorative approaches to prevent/delay cognitive deficits should target the conceptual neurovascular unit (NVU) rather than neurons alone. We have recently shown that there is augmented hippocampal NVU remodeling after a remote ischemic injury in diabetes. NLRP3 inflammasome signaling has been implicated in the development of diabetes and neurodegenerative diseases, but little is known about the impact of NLRP3 activation on functional and structural interaction within the NVU of hippocampus, a critical part of the brain that is involved in forming, organizing, and storing memories. Endothelial cells are at the center of the NVU and produce trophic factors such as brain derived neurotrophic factor (BDNF) contributing to neuronal survival, known as vasotrophic coupling. Therefore, the aims of this study focused on two hypotheses: 1) diabetes negatively impacts hippocampal NVU remodeling and worsens cognitive outcome after stroke, and 2) NLRP3 inhibition with MCC950 will improve NVU remodeling and cognitive outcome following stroke via vasotrophic (un)coupling between endothelial cells and hippocampal neurons. Stroke was induced through a 90-min transient middle cerebral artery occlusion (MCAO) in control and high-fat diet/streptozotocin-induced (HFD/STZ) diabetic male Wistar rats. Saline or MCC950 (3 mg/kg), an inhibitor of NLRP3, was injected at 1 and 3 h after reperfusion. Cognition was assessed over time and neuronal density, blood-brain barrier (BBB) permeability as well as NVU remodeling (aquaporin-4 [AQP4] polarity) was measured on day 14 after stroke. BDNF was measured in endothelial and hippocampal neuronal cultures under hypoxic and diabetes-mimicking condition with and without NLRP3 inhibition. Diabetes increased neuronal degeneration and BBB permeability, disrupted AQP4 polarity, impaired cognitive function and amplified NLRP3 activation after ischemia. Inhibition with MCC950 improved cognitive function and vascular integrity after stroke in diabetic animals and prevented hypoxia-mediated decrease in BDNF secretion. These results are the first to provide essential data showing MCC950 has the potential to become a therapeutic to prevent neurovascular remodeling and worsened cognitive decline in diabetic patients following stroke.

Alexander Bain's Mind and Body (1872): An underappreciated contribution to early neuropsychology

Alexander Bain (1818-1903) is well known for his two influential textbooks, The senses and the intellect (1855) and The emotions and the will (1859). In comparison, Bain's Mind and body: The theories of their relation (1872) has been of limited interest to historians, and it is here where he presents one of the first neural network models. This paper addresses the historical foundations of Bain's neural network model and explores some of his primary influences. Additionally, this study addresses some of the reasons Bain's Mind and Body did not receive the historical notice his earlier works garnered.

Long-term exercise training improves memory in middle-aged men and modulates peripheral levels of BDNF and Cathepsin B

Aging is accompanied by a decline in memory and other brain functions. Physical exercise may mitigate this decline through the modulation of factors participating in the crosstalk between skeletal muscle and the brain, such as neurotrophins and oxidative stress parameters. We aimed to determine whether long term exercise training (35 ± 15 years) promotes memory maintenance in middle-aged men, and to characterize the changes in neurotrophic factors and lipid oxidation markers in peripheral blood samples in both middle-aged and young men. The neuropsychological analysis showed significant improvements in memory through the Free and Cued Immediate Recall tests, in the middle-aged trained individuals when compared to the sedentary ones. We found a significant decrease in the resting serum BDNF and plasma Cathepsin B (CTSB) levels in the trained groups at both middle and young ages. BDNF and CTSB levels were inversely correlated with weekly hours of exercise. We also found a significant decrease in plasma malondialdehyde, an index of lipid peroxidation, in middle-aged and young trained subjects. The positive impact of long-term exercise training by delaying the onset of physiological memory loss and the associated neurotrophic and redox peripheral modulation, suggests the effectiveness of exercise as preventive strategy against age-related memory loss and neurodegeneration.

Treadmill Exercise Alleviates Circadian Rhythm Disruption-Induced Memory Deficits by Activation of Glucocorticoid Receptor and Brain-Derived Neurotrophic Factor-Dependent Pathway

Purpose

Circadian rhythm affects learning process, memory consolidation, and long-term memory. In this study, the alleviating effect of exercise on circadian rhythm disruption-induced memory deficits was investigated.

Methods

BMAL1 knockdown transgenic mice (BMAL1 TG) were used as the BMAL1-TG group and the BMAL1-TG with treadmill exercise group. Female C57BL/6J mice of the same age were used as the wildtype group and the wildtype with treadmill exercise group. The mice in the treadmill exercise groups performed running on a motorized treadmill under the dark-dark conditions for 8 weeks. Short-term memory, nonspatial object memory, and spatial learning memory were determined using stepdown avoidance test, novel object-recognition test, and radial 8-arm maze test. Immunohistochemistry for doublecortin and 5-bromo-2’-deoxyuridine was conducted for the determination of hippocampal neurogenesis. Using the western blot analysis, we determined the expressions of glucocorticoid receptor (GR) and factors related to the neurogenesis and memory consolidation, such as brain-derived neurotrophic factor, tyrosine kinase B, p44/42 mitogen-activated protein kinase, cyclic AMP-responsive element binding protein, phosphatidylinositol 3-kinase, protein kinas B, protein kinase C alpha, early-growth-response gene 1.

Results

Circadian rhythm disruption impaired memory function through inhibiting the expressions of GR and the factors related to neurogenesis and memory consolidation. Treadmill exercise improved memory function via enhancing the expressions of GR and above-mentioned factors.

Conclusions

Treadmill exercise acts as the zeitgeber that improves memory function under the circadian rhythm disrupted conditions.

Human Sensory LTP Predicts Memory Performance and Is Modulated by the BDNF Val66Met Polymorphism

Background: Long-term potentiation (LTP) is recognised as a core neuronal process underlying long-term memory. However, a direct relationship between LTP and human memory performance is yet to be demonstrated. The first aim of the current study was thus to assess the relationship between LTP and human long-term memory performance. With this also comes an opportunity to explore factors thought to mediate the relationship between LTP and long-term memory. The second aim of the current study was to explore the relationship between LTP and memory in groups differing with respect to brain-derived neurotrophic factor (BDNF) Val⁶⁶Met; a single-nucleotide polymorphism (SNP) implicated in memory function.

Methods: Participants were split into three genotype groups (Val/Val, Val/Met, Met/Met) and were presented with both an EEG paradigm for inducing LTP-like enhancements of the visually-evoked response, and a test of visual memory.

Results: The magnitude of LTP 40 min after induction was predictive of long-term memory performance. Additionally, the BDNF Met allele was associated with both reduced LTP and reduced memory performance.

Conclusions: The current study not only presents the first evidence for a relationship between sensory LTP and human memory performance, but also demonstrates how targeting this relationship can provide insight into factors implicated in variation in human memory performance. It is anticipated that this will be of utility to future clinical studies of disrupted memory function.

Transcriptomic changes triggered by ouabain in rat cerebellum granule cells: Role of α3- and α1-Na+,K+-ATPase-mediated signaling

It was shown previously that inhibition of the ubiquitous α1 isoform of Na+,K+-ATPase by ouabain sharply affects gene expression profile via elevation of intracellular [Na+]i/[K+]i ratio. Unlike other cells, neurons are abundant in the α3 isoform of Na+,K+-ATPase, whose affinity in rodents to ouabain is 104-fold higher compared to the α1 isoform. With these sharp differences in mind, we compared transcriptomic changes in rat cerebellum granule cells triggered by inhibition of α1- and α3-Na+,K+-ATPase isoforms. Inhibition of α1- and α3-Na+,K+-ATPase isoforms by 1 mM ouabain resulted in dissipation of transmembrane Na+ and K+ gradients and differential expression of 994 transcripts, whereas selective inhibition of α3-Na+,K+-ATPase isoform by 100 nM ouabain affected expression of 144 transcripts without any impact on the [Na+]i/[K+]i ratio. The list of genes whose expression was affected by 1 mM ouabain by more than 2-fold was abundant in intermediates of intracellular signaling and transcription regulators, including augmented content of Npas4, Fos, Junb, Atf3, and Klf4 mRNAs, whose upregulated expression was demonstrated in neurons subjected to electrical and glutamatergic stimulation. The role [Na+]i/[K+]i-mediated signaling in transcriptomic changes involved in memory formation and storage should be examined further.

Sex differences in antidepressant efficacy

Sex differences have been observed across many psychiatric diseases, especially mood disorders. For major depression, the most prevalent psychiatric disorder, females show a roughly two-fold greater risk as compared to males. Depression is sexually dimorphic with males and females exhibiting differences in clinical presentation, course, and response to antidepressant treatment. In this review, we first discuss sex differences observed in depressed patients, as well as animal models that reveal potential underlying mechanisms. We then discuss antidepressant treatments including their proposed mechanism of action and sex differences observed in treatment response. We include possible mechanisms underlying these sex differences with particular focus on synaptic transmission.

Mammalian Target of Rapamycin at the Crossroad Between Alzheimer's Disease and Diabetes

Accumulating evidence suggests that Alzheimer's disease may manifest as a metabolic disorder with pathology and/or dysfunction in numerous tissues. Adults with Alzheimer's disease suffer with significantly more comorbidities than demographically matched Medicare beneficiaries (Zhao et al, BMC Health Serv Res 8:108, 2008b). Reciprocally, comorbid health conditions increase the risk of developing Alzheimer's disease (Haaksma et al, PLoS One 12(5):e0177044, 2017). Type 2 diabetes mellitus is especially notable as the disease shares many overlapping pathologies observed in patients with Alzheimer's disease, including hyperglycemia, hyperinsulinemia, insulin resistance, glucose intolerance, dyslipidemia, inflammation, and cognitive dysfunction, as described in Chap. 8 of this book (Yoshitake et al, Neurology 45(6):1161-1168, 1995; Leibson et al, Am J Epidemiol 145(4):301-308, 1997; Ott et al, Neurology 53(9):1937-1942, 1999; Voisin et al, Rev Med Interne 24(Suppl 3):288s-291s, 2003; Janson et al. Diabetes 53(2):474-481, 2004; Ristow M, J Mol Med (Berl) 82(8):510-529, 2004; Whitmer et al, BMJ 330(7504):1360, 2005, Curr Alzheimer Res 4(2):103-109, 2007; Ohara et al, Neurology 77(12):1126-1134, 2011). Although nondiabetic older adults also experience age-related cognitive decline, diabetes is uniquely associated with a twofold increased risk of Alzheimer's disease, as described in Chap. 2 of this book (Yoshitake et al, Neurology 45(6):1161-1168, 1995; Leibson et al, Am J Epidemiol 145(4):301-308, 1997; Ott et al. Neurology 53(9):1937-1942, 1999; Ohara et al, Neurology 77(12):1126-1134, 2011). Good glycemic control has been shown to improve cognitive status (Cukierman-et al, Diabetes Care 32(2):221-226, 2009), and the use of insulin sensitizers is correlated with a lower rate of cognitive decline in older adults (Morris JK, Burns JM, Curr Neurol Neurosci Rep 12(5):520-527, 2012). At the molecular level, the mechanistic/mammalian target of rapamycin (mTOR) plays a key role in maintaining energy homeostasis. Nutrient availability and cellular stress information, both extracellular and intracellular, are integrated and transduced through mTOR signaling pathways. Aberrant regulation of mTOR occurs in the brains of patients with Alzheimer's disease and in numerous tissues of individuals with type 2 diabetes (Mannaa et al, J Mol Med (Berl) 91(10):1167-1175, 2013). Moreover, modulating mTOR activity with a pharmacological inhibitor, rapamycin, provides wide-ranging health benefits, including healthy life span extension in numerous model organisms (Vellai et al, Nature 426(6967):620, 2003; Jia et al, Development 131(16):3897-3906, 2004; Kapahi et al, Curr Biol 14(10):885-890, 2004; Kaeberlein et al, Science 310(5751):1193-1196, 2005; Powers et al, Genes Dev 20(2):174-184, 2006; Harrison et al, Nature 460(7253):392-395, 2009; Selman et al, Science 326(5949):140-144, 2009; Sharp ZD, Strong R, J Gerontol A Biol Sci Med Sci 65(6):580-589, 2010), which underscores its importance to overall organismal health and longevity. In this chapter, we discuss the physiological role of mTOR signaling and the consequences of mTOR dysregulation in the brain and peripheral tissues, with emphasis on its relevance to the development of Alzheimer's disease and link to type 2 diabetes.

Effects of a Cognitive Training With and Without Additional Physical Activity in Healthy Older Adults: A Follow-Up 1 Year After a Randomized Controlled Trial

Background: Combining cognitive training (CT) with physical activity (CPT) has been suggested to be most effective in maintaining cognition in healthy older adults, but data are scarce and inconsistent regarding long-term effects (follow-up; FU) and predictors of success.

Objective: To investigate the 1-year FU effects of CPT versus CT and CPT plus counseling (CPT+C), and to identify predictors for CPT success at FU.

Setting and Participants: We included 55 healthy older participants in the data analyses; 18 participants (CPT group) were used for the predictor analysis.

Interventions: In a randomized controlled trial, participants conducted a CT, CPT, or CPT+C for 7 weeks.

Outcome Measures: Overall cognition, verbal, figural, and working memory, verbal fluency, attention, planning, and visuo-construction.

Results: While within-group comparisons showed cognitive improvements for all types of training, only one significant interaction Group × Time favoring CPT in comparison to CPT+C was found for overall cognition and verbal long-term memory. The most consistent predictor for CPT success (in verbal short-term memory, verbal fluency, attention) was an initial low baseline performance. Lower education predicted working memory gains. Higher levels of insulin-like growth factor 1 (IGF-1) and lower levels of brain-derived neurotrophic factor at baseline (BDNF) predicted alternating letter verbal fluency gains.

Discussion: Within-group comparisons indicate that all used training types are helpful to maintain cognition. The fact that cognitive and sociodemographic data as well as nerve growth factors predict long-term benefits of CPT contributes to the understanding of the mechanisms underlying training success and may ultimately help to adapt training to individual profiles.

Clinical Trial Registration: WHO ICTRP (http://apps.who.int/trialsearch/), identifier DRKS00005194.

Autocrine signaling by an Aplysia neurotrophin forms a presynaptic positive feedback loop

Whereas short-term plasticity is often initiated on one side of the synapse, long-term plasticity involves coordinated changes on both sides, implying extracellular signaling. We have investigated the possible signaling role of an Aplysia neurotrophin (ApNT) in facilitation induced by serotonin (5HT) at sensory-to-motor neuron synapses in culture. ApNT is an ortholog of mammalian BDNF, which has been reported to act as either an anterograde, retrograde, or autocrine signal, so that its pre- and postsynaptic sources and targets remain unclear. We now report that ApNT acts as a presynaptic autocrine signal that forms part of a positive feedback loop with ApTrk and PKA. That loop stimulates spontaneous transmitter release, which recruits postsynaptic mechanisms, and presynaptic protein synthesis during the transition from short- to intermediate-term facilitation and may also initiate gene regulation to trigger the transition to long-term facilitation. These results suggest that a presynaptic ApNT feedback loop plays several key roles during consolidation of learning-related synaptic plasticity.

Calcium Release Mediated by Redox-Sensitive RyR2 Channels Has a Central Role in Hippocampal Structural Plasticity and Spatial Memory

AIMS

Previous studies indicate that hippocampal synaptic plasticity and spatial memory processes entail calcium release from intracellular stores mediated by ryanodine receptor (RyR) channels. In particular, RyR-mediated Ca²⁺ release is central for the dendritic spine remodeling induced by brain-derived neurotrophic factor (BDNF), a neurotrophin that stimulates complex signaling pathways leading to memory-associated protein synthesis and structural plasticity. To examine if upregulation of ryanodine receptor type-2 (RyR2) channels and the spine remodeling induced by BDNF entail reactive oxygen species (ROS) generation, and to test if RyR2 downregulation affects BDNF-induced spine remodeling and spatial memory.

RESULTS

Downregulation of RyR2 expression (short hairpin RNA [shRNA]) in primary hippocampal neurons, or inhibition of nitric oxide synthase (NOS) or NADPH oxidase, prevented agonist-mediated RyR-mediated Ca²⁺ release, whereas BDNF promoted cytoplasmic ROS generation. RyR2 downregulation or inhibitors of N-methyl-d-aspartate (NMDA) receptors, or NOS or of NADPH oxidase type-2 (NOX2) prevented RyR2 upregulation and the spine remodeling induced by BDNF, as did incubation with the antioxidant agent N-acetyl l-cysteine. In addition, intrahippocampal injection of RyR2-directed antisense oligodeoxynucleotides, which caused significant RyR2 downregulation, caused conspicuous defects in a memorized spatial memory task.

INNOVATION

The present novel results emphasize the key role of redox-sensitive Ca²⁺ release mediated by RyR2 channels for hippocampal structural plasticity and spatial memory.

CONCLUSION

Based on these combined results, we propose (i) that BDNF-induced RyR2-mediated Ca²⁺ release and ROS generation via NOS/NOX2 are strictly required for the dendritic spine remodeling and the RyR2 upregulation induced by BDNF, and (ii) that RyR2 channel expression is crucial for spatial memory processes. Antioxid. Redox Signal. 29, 1125-1146.

Endothelin-1 inhibition improves the mBDNF/proBDNF ratio in endothelial cells and HT22 neurons under high glucose/palmitate growth conditions

Diabetes increases the risk and worsens the progression of cognitive impairment. The hippocampus is an important domain for learning and memory. We previously showed that endothelin-1 (ET-1) reduced diabetes-induced inflammation in hippocampal neurons, suggesting a neuroprotective effect. Given that neurons and endothelial cells within the neurovascular unit depend on each other for proper function, we investigated the effect of ET-1 on brain-derived neurotrophic factor (BDNF) synthesis, a key neurotrophin and prosurvival factor, in neuronal (HT22 hippocampal neurons) and brain microvascular endothelial (BMEC-5i) cells under normal and diabetes-mimicking (high glucose plus palmitate) conditions. Cells were treated with exogenous ET-1 or ET receptor antagonists including ET(B) receptor selective antagonist BQ788 (1 microM) or dual-receptor antagonist bosentan (10 microM). Mature (m)BDNF, proBDNF and caspase-3 levels were measured by Western blotting. Diabetic conditions reduced the prosurvival mBDNF/proBDNF ratio in both HT22 and BMEC-5i cells. Addition of exogenous ET-1 had no effect on the BDNF system in HT22 cells in diabetic conditions. Both HT22 and BMEC-5i cells had an increase in the mBDNF/proBDNF ratio when grown in diabetes-simulating conditions in the presence of endothelin receptor inhibition. These data suggest that blockade of ET-1 may provide neuroprotection to hippocampal cells through the modulation of the BDNF system.

Effect of Acute Exercise Mode on Serum Brain-Derived Neurotrophic Factor (BDNF) and Task Switching Performance

Previous studies have consistently reported a positive effect of acute exercise on cognition, particularly on executive function. However, most studies have focused on aerobic and resistant forms of exercise. The purpose of this study was to compare the effect of ‘open-skill’ with ‘closed-skill’ exercise (defined in terms of the predictability of the performing environment) on brain-derived neurotrophic factor (BDNF) production and task switching performance. Twenty young adult males participated in both closed (running) and open (badminton) skill exercise sessions in a counterbalanced order on separate days. The exercise sessions consisted of 5 min of warm up exercises followed by 30 min of running or badminton. The exercise intensity was set at 60% (±5%) of the heart rate reserve level (HRR) with HR being monitored by a wireless heart rate monitor. Blood samples were taken and participation in a task-switching paradigm occurred before and after each exercise session. Results showed no differences in serum BDNF or task-switching performance at the pre-test stage, however, badminton exercise resulted in significantly higher serum BDNF levels (a proxy for levels of BDNF in the brain) and near significant smaller global switching costs relative to running. This study has provided preliminary evidence in support the relative benefits of open-skills exercises on BDNF and executive function.

ERα and/or ERβ activation ameliorates cognitive impairment, neurogenesis and apoptosis in type 2 diabetes mellitus mice

Estrogen receptors (ERs) are thought to be associated with the onset and progression of neurodegenerative injuries and diseases, but the relationship and mechanisms underlying between ERs and cognition in type 2 diabetes remain elusive. In the current study, we investigated the effects of ERα and ERβ on the cognition, neurogenesis and apoptosis in high-fat diet and streptozocin-induced diabetic mice. We found that ERα and/or ERβ activation using their agonists (0.5 mg/kg E2, PPT or DPN) ameliorate memory impairment in the Morris water maze and Y-maze tests, increase hippocampal neurogenesis and prevent hippocampal apoptotic responses. Importantly, treatment with the pharmacologic ERs agonists caused significant increases in the membrane ERα and ERβ expression and subsequent PI3K/Akt, CREB and BDNF activation in the hippocampus of type 2 diabetes mellitus mice. Our data indicate that ERα and ERβ are involved in the cognitive impairment in type 2 diabetes, and that activated ERs, such as application of ERs agonists, could be a novel and promising strategy for the treatment of diabetic cognitive impairment.

Activation of ERα and/or ERβ ameliorates cognitive impairment and apoptosis in streptozotocin-induced diabetic mice

Estrogen receptors (ERs) are thought to be associated with the onset and progression of neurodegenerative injuries and diseases, but the relationship and mechanisms underlying between ERs and cognition in type 1 diabetes remain elusive. In the current study, we investigated the effects of ERα and ERβ on the memory impairment and apoptosis in streptozotocin-induced diabetic mice. We found that ERα and/or ERβ activation using their agonists (0.5 mg/kg E2, PPT or DPN) ameliorate memory impairment in the Morris water maze (MWM) and Y-maze tests and suppress apoptosis as evidenced by decreased caspase-3 activity and increased ratio of Bcl-2/Bax. Importantly, treatment with the pharmacologic ERs agonists caused significant increases in the membrane ERα and ERβ expression and subsequent PI3K/Akt, CREB and BDNF activation in the hippocampus of diabetic mice. Our data indicate that ERα and ERβ are involved in the cognitive impairment of type 1 diabetes and that activation of ERs via administration of ERs agonists could be a novel and promising strategy for the treatment of diabetic cognitive impairment.

Hippocampal proBDNF facilitates place learning strategy associated with neural activity in rats

Mature brain-derived neurotrophic factor has been shown to have a promotive effect on synaptic plasticity and spatial memory. The precursor of BDNF (proBDNF) has emerged as a protein against its mature form. However, it is unknown whether and how proBDNF regulates neural excitability and spatial behavior. Through infusion of cleavage-resistant proBDNF or its antibody into HPC, we sought evidence for the influences by employing multiple behavioral tests and recording hippocampal single-unit activity. Our behavioral findings showed that proBDNF induced beneficial effects on spatial learning by facilitating the use of the place strategy and inhibiting the response strategy, including (1) using more place search strategies but less response strategies, and (2) increasing the number of rats in choosing place strategies but not response strategies. Intriguingly, infusion of an anti-proBDNF antibody did not affect rats' training process but rendered the adaption to learning reversal training more difficult, indicating deficits in choosing the proper learning strategy. The training-induced increase in proBDNF promoted the firing rate of pyramidal neurons but not fast-spiking (FS) interneurons. Importantly, endogenous proBDNF facilitated the neural correlate of spatial, but not response, learning behavior. However, the anti-proBDNF antibody effectively reversed the strategy preference and inhibited neural activity. We herein propose that proBDNF exerts pivotal effects on neural excitability and the use of cognitive strategies to facilitate the spatial learning process.

Maintenance of postsynaptic neuronal excitability by a positive feedback loop of postsynaptic BDNF expression

Experiments have demonstrated that in mice, the PVT strongly projects to the CeL and participates in the formation of fear memories by synaptic potentiation in the amygdala. Herein, we propose a mathematical model based on a positive feedback loop of BDNF expression and signaling to investigate PVT manipulation of synaptic potentiation. The model is validated by comparisons with experimental observations. We find that a high postsynaptic firing frequency after stimulation is induced by presynaptic Ca2+ when the rates of BDNF secretion from PVT and LA neurons to the CeL are above a threshold value. Moreover, the positive feedback of postsynaptic BDNF production is important for the maintenance of the high excitability of the SOM+ CeL neuron after stimulation. The model brings insight into the underlying mechanisms of PVT modulation of synaptic potentiation at LA-CeL synapses and provides a framework of understanding other similar processes associated with synaptic plasticity.

Contingency Training Alters Neurobiological Components of Emotional Resilience in Male and Female Rats

Prior research with a rat model of behavioral therapy [i.e., effort-based reward (EBR) contingency training] suggests that strengthened associations between physical effort and desired outcomes enhance neurobiological indices of resilience. In the current study, male and female Long-Evans rats were exposed to either six weeks of EBR training or noncontingent training prior to 10 days of exposure to chronic unpredictable stress (CUS). Subsequently, all animals were exposed to a problem-solving task and then trained in a spatial learning/foraging task, the Dry Land Maze (DLM). Following habituation training and test trials, rats were assessed in a probe trial that generated a prediction error (cognitive uncertainty). Results indicated that, during CUS exposure, contingency-training enhanced dehydroepiandrosterone/corticosterone ratios (consistent with healthier stress responses), especially in male rats. Additionally, contingency training increased exploratory behaviors in the probe trial as well as differentially influenced on-task problem-solving performance in males and females. Following the probe trial, brains were exposed to histological analyses to determine the effects of sex and contingency training on various neurobiological markers. Contingency training decreased BDNF-immunoreactivity (ir) in the hippocampus CA1 and lateral habenula, implicating differential neuroplasticity responses in the training groups. Further, coordinated fos-ir activation in areas associated with emotional resilience (i.e., motivation-regulation) was observed in contingent-trained animals. In sum, the current findings confirm that behavioral training is associated with neurobiological markers of emotional resilience; however, further assessments are necessary to more accurately determine the therapeutic potential for the EBR contingency training model.

Nicotine Modulates Cognitive Function in D-Galactose-Induced Senescence in Mice

Here, we tested the claim that nicotine attenuates the signs of brain dysfunction in the model of brain aging induced by D-galactose (DGal) in mice. We administered nicotine at doses of 0.1, 0.5 and 1 mg/kg by the subcutaneous (s.c.) or at 0.1 mg/kg by the intranasal (i.n.) routes in mice that had received DGal at the dose of 500 mg/kg subcutaneous (s.c.) for 6 weeks. We assessed animal withdrawal signs as the number of presented somatic signs, thermal hyperalgesia, elevated plus maze (EPM) and open field tests. We evaluated spatial memory and recognition with Barnes maze and novel object recognition (NOR) tests. We tested brain tissue for reactive oxygen species (ROS), mitochondrial membrane potential, caspase-3, Bax, Bcl-2, cytochrome C, brain-derived neurotrophic factor and nerve growth factor levels. Nicotine administration in model groups (0.5 mg/kg s.c. and 0.1 mg/kg i.n. doses) significantly attenuated impairment of spatial and episodic memories in comparison to normal saline-received model group. These doses also reduced mito-oxidative damage as well as apoptosis and raised neurotrophic factors level in model groups in comparison to normal saline-received model group. The 1 mg/kg s.c. dose nicotine revealed withdrawal signs compared with the other nicotine-received groups. Nicotine at specific doses and routes has the potential to attenuate age-related cognitive impairment, mito-oxidative damage, and apoptosis. The doses raise neurotrophic factors without producing withdrawal signs.

Melatonin ameliorates cognitive memory by regulation of cAMP-response element-binding protein expression and the anti-inflammatory response in a rat model of post-traumatic stress disorder

BACKGROUND

Post-traumatic stress disorder (PTSD) is an important psychological disease that can develop following the physical experience or witnessing of traumatic events. The psychopathological response to traumatic stressors increases inflammation in the hippocampus and induces memory deficits. Melatonin (MTG) plays critical roles in circadian rhythm disorders, Alzheimer's disease, and other neurological disorders. However, the cognitive efficiency of MTG and its mechanisms of action in the treatment of PTSD remain unclear. Thus, the present study investigated the effects of MTG on spatial cognitive impairments stimulated by single prolonged stress (SPS) in rats, an animal model of PTSD. Male rats received intraperitoneal (i.p.) administration of various doses of MTG for 21 consecutive days after the SPS procedure.

RESULTS

SPS-stimulated cognitive impairments in the object recognition task and Morris water maze were reversed by MTG treatment (25 mg/kg, i.p). Additionally, MTG significantly increased cognitive memory-related decreases in cAMP-response element-binding (CREB) protein and mRNA levels in the hippocampus. Our results also demonstrate that MTG significantly inhibited SPS-stimulated cognitive memory impairments by inhibiting the expression of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in the rat brain.

CONCLUSION

The present results indicate that MTG can be beneficial for SPS-stimulated memory impairments via changes in CREB expression and proinflammatory mediators. Thus, MTG may be a prophylactic strategy for the prevention or mitigation of the progression of some features of the PTSD pathology.

PI3K/Akt/GSK3β induced CREB activation ameliorates arsenic mediated alterations in NMDA receptors and associated signaling in rat hippocampus: Neuroprotective role of curcumin

Protective efficacy of curcumin in arsenic induced NMDA receptor dysfunctions and PI3K/Akt/ GSK3β signalling in hippocampus has been investigated in vivo and in vitro. Exposure to sodium arsenite (in vivo - 20 mg/kg, body weight p.o. for 28 days; in vitro - 10 μM for 24 h) and curcumin (in vivo - 100 mg/kg body weight p.o. for 28 days; in vitro - 20 μM for 24 h) was carried out alone or simultaneously. Treatment with curcumin ameliorated sodium arsenite induced alterations in the levels of NMDA receptors, its receptor subunits and synaptic proteins - pCaMKIIα, PSD-95 and SynGAP both in vivo and in vitro. Decreased levels of BDNF, pAkt, pERK1/2, pGSK3β and pCREB on sodium arsenite exposure were also protected by curcumin. Curcumin was found to decrease sodium arsenite induced changes in hippocampus by modulating PI3K/Akt/GSK3β neuronal survival pathway, known to regulate various cellular events. Treatment of hippocampal cultures with pharmacological inhibitors for ERK1/2, GSK3β and Akt individually inhibited levels of CREB and proteins associated with PI3K/Akt/GSK3β pathway. Simultaneous treatment with curcumin was found to improve sodium arsenite induced learning and memory deficits in rats assessed by water maze and Y-maze. The results provide evidence that curcumin exercises its neuroprotective effect involving PI3K/Akt pathway which may affect NMDA receptors and downstream signalling through TrKβ and BDNF in arsenic induced cognitive deficits in hippocampus.

Furin promotes dendritic morphogenesis and learning and memory in transgenic mice

Furin is a proprotein convertase implicated in a variety of pathological processes including neurodegenerative diseases. However, the role of furin in neuronal plasticity and learning and memory remains to be elucidated. Here, we report that in brain-specific furin transgenic (Furin-Tg) mice, the dendritic spine density and proliferation of neural progenitor cells were significantly increased. These mice exhibited enhanced long-term potentiation (LTP) and spatial learning and memory performance, without alterations of miniature excitatory/inhibitory postsynaptic currents. In the cortex and hippocampus of Furin-Tg mice, the ratio of mature brain-derived neurotrophic factor (mBDNF) to pro-BDNF, and the activities of extracellular signal-related kinase (ERK) and cAMP response element-binding protein (CREB) were significantly elevated. We also found that hippocampal knockdown of CREB diminished the facilitation of LTP and cognitive function in Furin-Tg mice. Together, our results demonstrate that furin enhances dendritic morphogenesis and learning and memory in transgenic mice, which may be associated with BDNF-ERK-CREB signaling pathway.

Validation of ethnopharmacology of ayurvedic sarasvata ghrita and comparative evaluation of its neuroprotective effect with modern alcoholic and lipid based extracts in β-amyloid induced memory impairment

ETHNOPHARMACOLOGICAL RELEVANCE

Sarasvata ghrita (SG), a polyherbal formulation from ayurveda, an ancient medicinal system of India, has been used to improve intelligence and memory, treat speech delay, speaking difficulties and low digestion power in children.

AIM OF THE STUDY

Study aimed to validate the ethno use of SG in memory enhancement through systematic scientific protocol. The effect of SG and modern extracts of ingredients of SG was compared on cognitive function and neuroprotection in amyloid-β peptide 25-35(Aβ25-35) induced memory impairment in wistar rats. Further the underlying mechanism for neuroprotective activity was investigated.

MATERIALS AND METHODS

SG was prepared as per traditional method, ethanolic extract (EE) was prepared by conventional method and lipid based extract was prepared by modern extraction method. All extracts were standardised by newly developed HPLC method with respect to marker compounds. SG, EE and LE were administered orally to male Wistar rats at doses of 100,200 and 400 mg/kg Body Weight by feeding needle for a period of 21 days after the intracerebroventricular administration of Aβ25-35 bilaterally. Spatial memory of rats was tested using Morris water maze (MWM) and Radial arm maze (RAM) test. The possible underlying mechanisms for the cognitive improvement exhibited by SG, EE and LE was investigated through ex-vivo brain antioxidant effect, monoamine level estimation, acetylcholine esterase (AchE) inhibitory effect and Brain-derived neurotropic factor (BDNF) levels estimation.

RESULTS

SG, EE and LE were analyzed by HPLC method, results showed that EE extract has high percent of selected phytoconstituents as compared with SG and LE. SG and LE decrease escape latency and searching distance in a dose dependant manner during MWM test. In case of RAM significant decrease in number of errors and increase in number of correct choices indicate an elevation in retention and recall aspects of learning and memory after administration of SG an LE. SG and LE extract can efficiently prevent accumulation of β-amyloid plaque in hippocampus region. There was increase in SOD, GSH, CAT and NO level and decrease in MDA levels in SG and LE administered animals. SG and LE have found to exhibit AchE inhibitiory activity and significant dose-dependant increase in BDNF level in the plasma. SG and LE significantly increased the levels of noradrenaline, dopamine and 5-hydroxytryptamine in the brain.

CONCLUSION

The study validated the neuroprotective activity of SG. The study concludes the extraction efficiency of SG for selected phytoconstituents is less than modern methods. However the neuroprotective activity of SG and LE was found to be greater than EE.

Aging and an Immune Challenge Interact to Produce Prolonged, but Not Permanent, Reductions in Hippocampal L-LTP and mBDNF in a Rodent Model with Features of Delirium

Aging increases the risk of abrupt declines in cognitive function after an event that triggers immune system activation (e.g. surgery, infection, or injury). This phenomenon is poorly understood, but rodent models may provide clues. We have previously shown that aging (24-mo-old) F344xBN rats generally do not show significant physical or cognitive impairments. However, their brains mount an exaggerated inflammatory response to signals triggered by a peripheral immune challenge (an intraperitoneal injection of Escherichia coli or laparotomy). Their hippocampal levels of the proinflammatory cytokine IL-1β are significantly elevated for at least 8 d, but generally less than 14 d, after infection or surgery. This IL-1β elevation is mirrored by prolonged deficits in a hippocampus-dependent long-term memory task. In contrast, young (3-mo-old) counterparts exhibit only transient elevations in IL-1β that drop to near baseline levels within 24 h. We previously demonstrated that theta burst–evoked late-phase long-term potentiation (L-LTP)—a BDNF-dependent form of synaptic plasticity—is impaired in hippocampal area CA1 of aged animals 4 d after infection. Also, levels of mature brain-derived neurotrophic factor (mBDNF)—the protein isoform required for stabilization of L-LTP—are reduced in hippocampal synaptoneurosomes of aged animals at the same time point. In this study, we investigated whether the deficits in L-LTP and mBDNF persist in parallel with the elevation in IL-1β and impairment in memory. This was the case, consistent with the idea that an exaggerated brain inflammatory response may compromise memory consolidation in part by altering availability of mBDNF to stabilize memory-related synaptic plasticity.

Acute exercise induced BDNF-TrkB signalling is intact in the prefrontal cortex of obese, glucose-intolerant male mice

Obesity and glucose intolerance have been directly implicated in the pathology of Alzheimer's disease. It is thought that diet-induced obesity causes a reduction in neuronal plasticity through a reduction in the neurotrophin: brain-derived neurotrophic factor (BDNF). Previous work has demonstrated that acute exercise in healthy lean animals increases BDNF-TrkB signalling in the brain. However, if this effect is intact in a state of obesity remains unknown. The purpose of this study is to determine the effects of a single bout of exercise on BDNF-TrkB signalling in the prefrontal cortex and hippocampus from obese glucose intolerant mice. Male C57BL/6 mice were fed a low-fat diet (10% kcals from lard) or a high-fat diet (HFD, 60% kcals from lard) for 7 weeks. A subset of HFD mice underwent an acute bout of exercise (treadmill running: 15 m/min, 5% incline, 120 min) followed by a recovery period of 2 h, after which point the prefrontal cortex and hippocampus were collected. The HFD increased body mass and glucose intolerance (p < 0.05). Prefrontal cortex from HFD mice demonstrated lower BDNF protein content, reduced phosphorylation of the BDNF receptor (TrkB), and its downstream effector cAMP response element-binding protein (CREB), as well as PGC-1α and ERα) protein content (p < 0.05). Two hours following the acute exercise bout, TrkB and CREB phosphorylation as well as PGC-1α and ER-α protein content were recovered (p < 0.05). Our findings demonstrate for the first time that an acute bout of exercise can recover BDNF-TrkB signalling in the prefrontal cortex of obese mice.

A brief primer on the mediational role of BDNF in the exercise-memory link

One of the most amazing aspects of the human brain is its ability to learn information and use it to change behaviour. A key neurotrophin that influences memory function is brain-derived neurotrophic factor (BDNF). This review briefly discusses the mechanistic role that BDNF may play in facilitating learning and memory. We also describe the role of exercise on this relationship. As discussed herein, BDNF may influence memory via BDNF-induced alterations in membrane receptor expression and translocation, as well as activating several pathways (PLC-y, PI3K, ERK) that act together to facilitate cellular effects that influence synaptic plasticity. Exercise may help to facilitate BDNF expression and its downstream cellular pathways from both direct and indirect mechanisms.

Underlying Mechanisms of Cooperativity, Input Specificity, and Associativity of Long-Term Potentiation Through a Positive Feedback of Local Protein Synthesis

Long-term potentiation (LTP) is a specific form of activity-dependent synaptic plasticity that is a leading mechanism of learning and memory in mammals. The properties of cooperativity, input specificity, and associativity are essential for LTP; however, the underlying mechanisms are unclear. Here, based on experimentally observed phenomena, we introduce a computational model of synaptic plasticity in a pyramidal cell to explore the mechanisms responsible for the cooperativity, input specificity, and associativity of LTP. The model is based on molecular processes involved in synaptic plasticity and integrates gene expression involved in the regulation of neuronal activity. In the model, we introduce a local positive feedback loop of protein synthesis at each synapse, which is essential for bimodal response and synapse specificity. Bifurcation analysis of the local positive feedback loop of brain-derived neurotrophic factor (BDNF) signaling illustrates the existence of bistability, which is the basis of LTP induction. The local bifurcation diagram provides guidance for the realization of LTP, and the projection of whole system trajectories onto the two-parameter bifurcation diagram confirms the predictions obtained from bifurcation analysis. Moreover, model analysis shows that pre- and postsynaptic components are required to achieve the three properties of LTP. This study provides insights into the mechanisms underlying the cooperativity, input specificity, and associativity of LTP, and the further construction of neural networks for learning and memory.

Brain-derived neurotrophic factor acts at neurons of the subfornical organ to influence cardiovascular function

Brain-derived neurotrophic factor (BDNF), a neurotrophin traditionally associated with neural plasticity, has more recently been implicated in fluid balance and cardiovascular regulation. It is abundantly expressed in both the central nervous system (CNS) and peripheral tissue, and is also found in circulation. Studies suggest that circulating BDNF may influence the CNS through actions at the subfornical organ (SFO), a circumventricular organ (CVO) characterized by the lack of a normal blood-brain barrier (BBB). The SFO, well-known for its involvement in cardiovascular regulation, has been shown to express BDNF mRNA and mRNA for the TrkB receptor at which BDNF preferentially binds. This study was undertaken to determine if: (1) BDNF influences the excitability of SFO neurons in vitro; and (2) the cardiovascular consequences of direct administration of BDNF into the SFO of anesthetized rats. Electrophysiological studies revealed that bath application of BDNF (1 nmol/L) influenced the excitability of the majority of neurons (60%, n = 13/22), the majority of which exhibited a membrane depolarization (13.8 ± 2.5 mV, n = 9) with the remaining affected cells exhibiting hyperpolarizations (-11.1 ± 2.3 mV, n = 4). BDNF microinjections into the SFO of anesthetized rats caused a significant decrease in blood pressure (mean [area under the curve] AUC = -364.4 ± 89.0 mmHg × sec, n = 5) with no effects on heart rate (mean AUC = -12.2 ± 3.4, n = 5). Together these observations suggest the SFO to be a CNS site at which circulating BDNF could exert its effects on cardiovascular regulation.

Moringa oleifera Seed Extract Alleviates Scopolamine-Induced Learning and Memory Impairment in Mice

The extract of Moringa oleifera seeds has been shown to possess various pharmacological properties. In the present study, we assessed the neuropharmacological effects of 70% ethanolic M. oleifera seed extract (MSE) on cognitive impairment caused by scopolamine injection in mice using the passive avoidance and Morris water maze (MWM) tests. MSE (250 or 500 mg/kg) was administered to mice by oral gavage for 7 or 14 days, and cognitive impairment was induced by intraperitoneal injection of scopolamine (4 mg/kg) for 1 or 6 days. Mice that received scopolamine alone showed impaired learning and memory retention and considerably decreased cholinergic system reactivity and neurogenesis in the hippocampus. MSE pretreatment significantly ameliorated scopolamine-induced cognitive impairment and enhanced cholinergic system reactivity and neurogenesis in the hippocampus. Additionally, the protein expressions of phosphorylated Akt, ERK1/2, and CREB in the hippocampus were significantly decreased by scopolamine, but these decreases were reversed by MSE treatment. These results suggest that MSE-induced ameliorative cognitive effects are mediated by enhancement of the cholinergic neurotransmission system and neurogenesis via activation of the Akt, ERK1/2, and CREB signaling pathways. These findings suggest that MSE could be a potent neuropharmacological drug against amnesia, and its mechanism might be modulation of cholinergic activity via the Akt, ERK1/2, and CREB signaling pathways.

Memory Function in Feeding Habit Transformation of Mandarin Fish (Siniperca chuatsi)

Mandarin fish refuse dead prey fish or artificial diets and can be trained to transform their inborn feeding habit. To investigate the effect of memory on feeding habit transformation, we compared the reaction time to dead prey fish and the success rate of feeding habit transformation to dead prey fish with training of mandarin fish in the 1st experimental group (trained once) and the 2nd experimental group (trained twice). The mandarin fish in the 2nd group had higher success rate of feeding habit transformation (100%) than those in the 1st group (67%), and shorter reaction time to dead prey fish (<1 s) than those in the 1st group (>1 s). Gene expression of cAMP responsive element binding protein I (Creb I), brain-derived neurotrophic factor (Bdnf), CCAAT enhancer binding protein delta (C/EBPD), fos-related antigen 2 (Fra2), and proto-oncogenes c-fos (c-fos) involved in long-term memory formation were significantly increased in the 2nd group after repeated training, and taste 1 receptor member 1 (T1R1), involved in feeding habit formation, was significantly increased in brains of the 2nd group after repeated training. DNA methylation levels at five candidate CpG (cytosine–guanine) sites contained in the predicted CpG island in the 5′-flanking region of T1R1 were significantly decreased in brains of the 2nd group compared with that of the 1st group. These results indicated that the repeated training can improve the feeding habit transformation through the memory formation of accepting dead prey fish. DNA methylation of the T1R1 might be a regulatory factor for feeding habit transformation from live prey fish to dead prey fish in mandarin fish.

Chronic treatment with the new anticonvulsant drug lacosamide impairs learning and memory processes in rats: A possible role of BDNF/TrkB ligand receptor system

Cognitive impairment is considered a frequent side effect in the drug treatment of epilepsy. The objective of the present study was to investigate the effects of lacosamide (LCM) on learning and memory processes in rats, on the serum level of brain-derived neurotrophic factor (BDNF) and BDNF/TrkB ligand receptor system expression in the hippocampal formation. Male Wistar rats underwent long-term treatment with three different doses of lacosamide - 3 mg/kg (LCM 3), 10 mg/kg (LCM 10) and 30 mg/kg (LCM 30). All rats were subjected to one active and one passive avoidance tests. The BDNF/TrkB immunohistochemical expression in the hippocampus was measured and serum BDNF was determined. The LCM-treated rats made fewer avoidance responses than controls during acquisition training and in the memory retention test. The number of escapes in the LCM 10 and LCM 30 groups decreased throughout the test, while the rats in the LCM 3 group showed fewer escapes only in the memory test in the active avoidance task. In the step-down test, the latency time of the LCM-30 treated rats was reduced as compared with the controls during the learning session and the short- and long-term memory retention tests. Lacosamide induced a dose-dependent reduction of the hippocampal expression of BDNF and its receptor TrkB. We found no significant difference between BDNF serum levels in the test animals and controls. The results of the study suggest that LCM suppresses the learning and memory processes in rats, with the inhibition of hippocampal BDNF/TrkB ligand receptor system being one of the possible mechanisms causing this effect.

15-Year Secular Trends in Cognitive Function Among Older Adults in the United States

Cognitive impairment is associated with various chronic diseases, including mobility limitation and early mortality. Thus, evaluating changes in cognition is of paramount public health interest. The purpose of this study was to evaluate secular trends in cognitive function among a representative sample of the U.S. older adult population. Data from the 1999-2000, 2001-2002, 2011-2012, and 2013-2014 National Health and Nutrition Examination Survey were utilized to identify an aggregate sample of adults 60+ years of age. The sample size across the four respective cycles was 1417, 1558, 1422, and 1592. Three cognitive assessments were employed, including the CERAD Word Learning subset (Consortium to Establish a Registry for Alzheimer's disease), the Animal Fluency test, and the Digit Symbol Substitution Test (DSST). For the entire sample and several subpopulations, DSST scores increased from 1999 to 2012 and then decreased in the 2013 to 2014 cycle. For all CERAD trials, there was evidence of increased CERAD performance from 2011-2012 to 2013-2014. No secular trends were observed for the Animal Fluency task across these cycles. Select cognitive parameters appear to be improving among U.S. older adults. Future work is needed to further explore secular trends in cognitive sustainability, and, as evidenced by our present study, cognitive enrichment over time.

Epigenetic regulation of Fgf1 transcription by CRTC1 and memory enhancement

Recent evidence demonstrates that epigenetic regulation of gene transcription is critically involved in learning and memory. Here, we discuss the role of histone acetylation and DNA methylation, which are two best understood epigenetic processes in memory processes. More specifically, we focus on learning-strength-dependent changes in chromatin on the fibroblast growth factor 1 (Fgf1) gene and on the molecular events that modulate regulation of Fgf1 transcription, required for memory enhancement, with the specific focus on CREB-regulated transcription coactivator 1 (CRTC1).

Effect of a Comprehensive Intervention on Plasma BDNF in Patients with Alzheimer's Disease

A comprehensive intervention (CI) on patients with Alzheimer’s disease was assessed by measuring plasmabrain-derived neurotrophic factor (pBDNF) and ADAS-Cog score (ADAS-Cog_score) before, immediately after (FU1), and 6 (FU2) and 24 months (FU3) after the CI. Baseline pBDNF was higher in patients with moderate AD (but not mild AD) than in healthy controls. At FU1, pBDNF and ADAS-Cog_score decreased significantly. At FU2 and FU3, patients’ cognitive status worsened and pBDNF further increased versus baseline, suggesting that CI interruption may be a stress event that prevents return to homeostasis. CI exerted positive short-term effects, but more information is needed on long-term consequences.

Requirement of an Early Activation of BDNF/c-Fos Cascade in the Retrosplenial Cortex for the Persistence of a Long-Lasting Aversive Memory

During the past few years, there has been growing interest in the role of the retrosplenial cortex (RSC) in memory processing. However, little is known about the molecular changes that take place in this brain region during memory formation. In the present work, we studied the early post-training participation of RSC in the formation of a long-lasting memory in rats. We found an increase in c-Fos levels in the anterior part of the RSC (aRSC) after inhibitory avoidance (IA) training. Interestingly, this increase was associated with memory durability, since blocking c-Fos expression using specific antisense oligonucleotides (ASO) impaired long-lasting retention 7 days after training without affecting memory expression 2 days after training. In addition, we showed that BDNF is one of the upstream signals for c-Fos expression required for memory persistence, since blocking BDNF synthesis prevents IA training-induced increase in c-Fos levels in aRSC and affects memory persistence. In addition, we found that injection of BDNF into aRSC around training was sufficient to establish a persistent memory and that this effect was prevented by c-fos ASO infusion into the same structure. These findings reveal an early post-training involvement of aRSC in the processing of a long-lasting aversive memory.

Recommendation on test readiness criteria for new approach methods in toxicology: Exemplified for developmental neurotoxicity

Multiple non-animal-based test methods have never been formally validated. In order to use such new approach methods (NAMs) in a regulatory context, criteria to define their readiness are necessary. The field of developmental neurotoxicity (DNT) testing is used to exemplify the application of readiness criteria. The costs and number of untested chemicals are overwhelming for in vivo DNT testing. Thus, there is a need for inexpensive, high-throughput NAMs, to obtain initial information on potential hazards, and to allow prioritization for further testing. A background on the regulatory and scientific status of DNT testing is provided showing different types of test readiness levels, depending on the intended use of data from NAMs. Readiness criteria, compiled during a stakeholder workshop, uniting scientists from academia, industry and regulatory authorities are presented. An important step beyond the listing of criteria, was the suggestion for a preliminary scoring scheme. On this basis a (semi)-quantitative analysis process was assembled on test readiness of 17 NAMs with respect to various uses (e.g. prioritization/screening, risk assessment). The scoring results suggest that several assays are currently at high readiness levels. Therefore, suggestions are made on how DNT NAMs may be assembled into an integrated approach to testing and assessment (IATA). In parallel, the testing state in these assays was compiled for more than 1000 compounds. Finally, a vision is presented on how further NAM development may be guided by knowledge of signaling pathways necessary for brain development, DNT pathophysiology, and relevant adverse outcome pathways (AOP).

Cognitive-Enhancing Effects of a Polyphenols-Rich Extract from Fruits without Changes in Neuropathology in an Animal Model of Alzheimer's Disease

No effective preventive treatment is available for age-related cognitive decline and Alzheimer's disease (AD). Epidemiological studies indicate that a diet rich in fruit is associated with cognitive improvement. It was thus proposed that high polyphenol concentrations found in berries can prevent cognitive impairment associated with aging and AD. Therefore, the Neurophenols project aimed at investigating the effects of a polyphenolic extract from blueberries and grapes (PEBG) in the triple-transgenic (3xTg-AD) mouse model of AD, which develops AD neuropathological markers, including amyloid-β plaques and neurofibrillary tangles, leading to memory deficits. In this study, 12-month-old 3xTg-AD and NonTg mice were fed a diet supplemented with standardized PEBG (500 or 2500 mg/kg) for 4 months (n = 15-20/group). A cognitive evaluation with the novel object recognition test was performed at 15 months of age and mice were sacrificed at 16 months of age. We observed that PEBG supplementation with doses of 500 or 2500 mg/kg prevented the decrease in novel object recognition observed in both 15-month-old 3xTg-AD mice and NonTg mice fed a control diet. Although PEBG treatment did not reduce Aβ and tau pathologies, it prevented the decrease in mature BDNF observed in 16-month-old 3xTg-AD mice. Finally, plasma concentrations of phenolic metabolites, such as dihydroxyphenyl valerolactone, a microbial metabolite of epicatechin, positively correlated with memory performances in supplemented mice. The improvement in object recognition observed in 3xTg-AD mice after PEBG administration supports the consumption of polyphenols-rich extracts to prevent memory impairment associated with age-related disease, without significant effects on classical AD neuropathology.

Neonatal Exposure to Low-Dose (1.2%) Sevoflurane Increases Rats' Hippocampal Neurogenesis and Synaptic Plasticity in Later Life

The increasing usage of general anesthetics on young children and infants has drawn extensive attention to the effects of these drugs on cognitive function later in life. Recent animal studies have revealed improvement in hippocampus-dependent performance after lower concentrations of sevoflurane exposure. However, the long-term effects of low-dose sevoflurane on the developing brain remain elusive. On postnatal day (P) 7, rats were treated with 1.2% sevoflurane (1.2% sevo group), 2.4% sevoflurane (2.4% sevo group), and air control (C group) for 6 h. On P35-40, rats' hippocampus-dependent learning and memory was tested using the Morris water maze. Cognition-related and synapse-related proteins in the hippocampus were measured using Western blotting on P35. On the same day, neurogenesis and synapse ultrastructure were evaluated using immunofluorescence and transmission electron microscopy (TEM). On P35, the rats neonatally exposed to 1.2% sevoflurane showed better behavioral results than control rats, but not in the 2.4% sevo group. Exposure to 1.2% sevoflurane increased the number of 5'-bromo-2-deoxyuridine (BrdU)-positive cells in the dentate gyrus and improved both synaptic number and ultrastructure in the hippocampus. The expression levels of BDNF, TrkB, postsynaptic density (PSD)-95, and synaptophysin in the hippocampus were also increased in the 1.2% sevo group. In contrast, no significant changes in neurogenesis or synaptic plasticity were observed between the C group and the 2.4% sevo group on P35. These results showed that exposure of the developing brain to a low concentration of sevoflurane for 6 h could promote spatial learning and memory function, along with increased hippocampal neurogenesis and synaptic plasticity, in later life.

Exenatide exerts cognitive effects by modulating the BDNF-TrkB neurotrophic axis in adult mice

Modulation of insulin-dependent signaling is emerging as a valuable therapeutic tool to target neurodegeneration. In the brain, the activation of insulin receptors promotes cell growth, neuronal repair, and protection. Altered brain insulin signaling participates in the cognitive decline seen in Alzheimer's disease patients and the aging brain. Glucagon-like peptide-1 (GLP-1) regulates insulin secretion and, along with GLP-1 analogues, enhances neurotrophic signaling and counteracts cognitive deficits in preclinical models of neurodegeneration. Moreover, recent evidence indicates that GLP-1 modulates the activity of the brain-derived neurotrophic factor (BDNF). In this study, in adult wild-type mice, here employed as a model of mid-life brain aging, we evaluated the effects of a 2-month treatment with exenatide, a GLP-1 analogue. We found that exenatide promotes the enhancement of long-term memory performances. Biochemical and imaging analyses show that the drug promotes the activation of the BDNF-TrkB neurotrophic axis and inhibits apoptosis by decreasing p75NTR-mediated signaling. The study provides preclinical evidence for the use of exenatide to delay age-dependent cognitive decline.

The effect of postnatal manganese exposure on the NMDA receptor signaling pathway in rat hippocampus

Overexposure to manganese (Mn) is associated with neurological disorders in children. Evidence indicated that N-methyl-d-aspartate (NMDA) receptor signaling pathway was critical for neurobehavioral function. However, whether NMDA receptor signaling pathway contributes to Mn-induced neurotoxicity remains unknown. In this study, newborn Sprague-Dawley rats were randomly assigned to four groups exposed to 0, 10, 20, and 30 mg/kg of Mn²⁺ by intraperitoneal injection (n = 10/group: five males and five females). After 3 weeks of Mn exposure, messenger RNA (mRNA) and protein expression of NMDA receptor subunits (NR1, NR2A, and NR2B), cAMP-response element binding protein (CREB), and brain-derived neurotrophic factor (BDNF) in hippocampus were measured by real-time quantitative RT-PCR and Western blot. In Mn-exposed rats, decreased mRNA and protein expression of NR1, NR2A, and NR2B, CREB, and BDNF was observed. The results imply that downregulated NMDA receptor signaling pathway may be of vital importance in the neuropathological process of Mn-induced neurotoxicity.

Computerized cognitive training and brain derived neurotrophic factor during bed rest: mechanisms to protect individual during acute stress

Acute stress, as bed rest, was shown to increase plasma level of the neurotrophin brain-derived neurotrophic factor (BDNF) in older, but not in young adults. This increase might represent a protective mechanism towards acute insults in aging subjects. Since computerized cognitive training (CCT) is known to protect brain, herein we evaluated the effect of CCT during bed rest on BDNF, muscle mass, neuromuscular function and metabolic parameters. The subjects that underwent CCT did not show an increase of BDNF after bed rest, and showed an anti-insular modification pattern in metabolism. Neuromuscular function parameters, already shown to beneficiate from CCT, negatively correlated with BDNF in research participants undergoing CCT, while positively correlated in the control group. In conclusion, BDNF increase can be interpreted as a standardized protective mechanism taking place whenever an insult occurs; it gives low, but consistent preservation of neuromuscular function. CCT, acting as an external protective mechanism, seems to modify this standardized response, avoiding BDNF increase or possibly modifying its time course. Our results suggest the possibility of differential neuroprotective mechanisms among ill and healthy individuals, and the importance of timing in determining the effects of protective mechanisms.

Daily supplementation with GrandFusion® improves memory and learning in aged rats

Studies have shown that supplementation with extracts from various sources, including fruits and vegetables reverse the age-related changes in movement and cognition. We hypothesized that these beneficial effects result from the presence of anti-oxidants and anti-inflammatory compounds in the fruits and vegetables that contribute to reduced oxidative stress, inflammation and cell death while potentially enhancing neurogenesis. The present study was performed to determine the impact of supplementation with GrandFusion^®(GF) to aged Fisher 344 rats for 4 months to determine the impact on attenuation or reversal of the age-related deficits. When the aged rats consumed a diet enriched with the extracts the results showed an improved motor performance, and enhanced cognitive functions. In addition, the rats showed reduced oxidative stress and inflammation, and enhanced neurogenesis, Nrf2 and anti-oxidant expression. The effect of GF extracts on the augmentation of memory and learning is significant and may function through the modulation of antioxidant enzymes, signaling pathways and additional mechanisms to improve the aging process. These studies further support the recommendation of USDA for the consumption of fruits and vegetables to improve healthy aging.

Regulation and effects of neurotrophic factors after neural stem cell transplantation in a transgenic mouse model of Alzheimer disease

According to much research, neurodegeneration and cognitive decline in Alzheimer disease (AD) are correlated with alternations of neurotrophic factors such as nerve growth factor, brain-derived neurotrophic factor, and glial cell-derived neurotrophic factor. The experimental illumination of neural stem cell (NSC) transplantation to eliminate AD symptoms is being explored frequently, and we have acknowledged that neurotrophic factors may play a pivotal role in cognitive improvement. However, the relation between the reversal of cognitive deficits after NSC transplantation and directed alternations of neurotrophic factors is not clearly expounded. Meanwhile, reduced inflammatory response, promoted vessel density, and vascular endothelial growth factor (VEGF) can be reflections of improvement in cerebrovascular function. Three weeks after NSC transplantation, spatial learning and memory function in NSC-injected (Tg-NSC) mice were significantly improved compared with vehicle-injected (Tg-Veh) mice. Meanwhile, results obtained by immunofluorescence and Western blot analyses demonstrated that the levels of neurotrophic factors, VEGF, and vessel density in the cortex of Tg-NSC mice were significantly enhanced compared with Tg-Veh mice, while the levels of proinflammatory cytokines interleukin (IL)-1β, tumor necrosis factor-α, and IL-6 were significantly decreased. Our results suggest that elevated concentrations of neurotrophic factors probably play a critical role in rescuing cognitive dysfunction in APP/PS1 transgenic mice after NSC transplantation, and neurotrophic factors may improve cerebrovascular function by means such as reducing inflammatory response and promoting angiogenesis.