Metabolic regulation of neuronal plasticity by the energy sensor AMPK

Therapeutic effects of metformin on cocaine conditioned place preference and locomotion

Lack of Food and Drug Administration-approved treatments for cocaine use disorder contributes to high rates of treatment attrition, relapse, and overdose. Metformin is a Type 2 diabetes drug being investigated for multiple new therapeutic indications. This study set out to determine whether metformin would impact the conditioned rewarding effects of cocaine in an abbreviated or standard two-chamber conditioned place preference (CPP) assay. Adult male (n = 73) and female (n = 82) Sprague Dawley rats were conditioned in a 7-day (abbreviated: 2 × 30 min sessions daily) or a 12-day timeline (standard: 1 × 30 min sessions daily) alternating control and treatment sessions using an unbiased design. Metformin (175 mg/kg) or saline pretreatment occurred 30 min before conditioning with cocaine (20 mg/kg) or vehicle (saline). Data showed sex differences in physiological responses to cocaine and metformin, as well as variant behavioral patterns with different conditioning paradigms. Metformin pretreatment impaired acquisition of cocaine CPP in abbreviated, but not standard conditioning among male rats only. Cocaine-induced locomotor effects are moderated with metformin pretreatment in both female and male rats in different phases of conditioning, suggesting the potential therapeutic value of symptom alleviation when tapering patients off cocaine use with the goal of abstinence. Sex differences observed highlight the importance in better understanding the unique pharmacological profiles of female and male patients. This study provides evidence supporting the potential repurposing of metformin for disrupting rewarding and psychomotor effects of cocaine, paving the way for safe, low-cost, and accessible treatment. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

Epilepsy and autophagy modulators: a therapeutic split

Epilepsy is a neurological disease characterized by repeated unprovoked seizure. Epilepsy is controlled by anti-epileptic drugs (AEDs); however, one third of epileptic patients have symptoms that are not controlled by AEDs in a condition called refractory epilepsy. Dysregulation of macroautophagy/autophagy is involved in the pathogenesis of epilepsy. Autophagy prevents the development and progression of epilepsy through regulating the balance between inhibitory and excitatory neurotransmitters. Induction of autophagy and autophagy-related proteins could be a novel therapeutic strategy in the management of epilepsy. Despite the protective role of autophagy against epileptogenesis and epilepsy, its role in status epilepticus is perplexing and might reflect its nature as a double-edged sword. Autophagy inducers play a critical role in reducing seizure frequency and severity, and could be an adjuvant treatment in the management of epilepsy. However, autophagy inhibitors also have an anticonvulsant effect. Therefore, the aim of the present mini-review is to discuss the potential role of autophagy in the pathogenesis of epileptogenesis and epilepsy, and how autophagy modulators affect epileptogenesis and epilepsy.

Research on the effects of different sugar substitutes-Mogroside V, Stevioside, Sucralose, and Erythritol-On glucose, lipid, and protein metabolism in type 2 diabetic mice

Sugar substitutes that maintain the homeostasis of glucose, lipid, and protein metabolism are important for nutritional intervention in type 2 diabetes mellitus (T2DM). However, the specific metabolic effects remain unclear. The aim of this study was to systematically compare the effects of four common sugar substitutes on a high-fat diet (HFD) combined with a streptozotocin (STZ)-induced T2DM mouse model from the perspective of hepatic glucose, lipid, and protein metabolism. In this study, based on the establishment of a T2DM mouse model induced by an HFD combined with STZ and nontargeted metabolomics, the effects of four sugar substitutes on regulating and improving sugar, lipid, and protein metabolism were systematically evaluated. The results showed that mogroside V (MOG), stevioside (ST), and erythritol (ERT) enhanced protein synthesis via the mammalian target of the rapamycin/p-P70S6K pathway. MOG and ST also improved glucose and lipid metabolism by activating the phosphor-AMP-activated protein kinase (p-AMPK) pathway and upregulating peroxisome proliferator-activated receptor alpha/carnitine palmitoyltransferase 1. Sucralose primarily improves lipid metabolism by downregulating sterol regulatory element-binding protein 1, whereas ERT increases lipid droplet accumulation in the liver. These findings provide a foundation for the application of sugar substitutes in T2DM nutritional interventions.

Sleep loss is a metabolic disorder

Sleep loss dysregulates cellular metabolism and energy homeostasis. Highly metabolically active cells, such as neurons, enter a catabolic state during periods of sleep loss, which consequently disrupts physiological functioning. Specific to the central nervous system, sleep loss results in impaired synaptogenesis and long-term memory, effects that are also characteristic of neurodegenerative diseases. In this review, we describe how sleep deprivation increases resting energy expenditure, leading to the development of a negative energy balance-a state with insufficient metabolic resources to support energy expenditure-in highly active cells like neurons. This disruption of energetic homeostasis alters the balance of metabolites, including adenosine, lactate, and lipid peroxides, such that energetically costly processes, such as synapse formation, are attenuated. During sleep loss, metabolically active cells shunt energetic resources away from those processes that are not acutely essential, like memory formation, to support cell survival. Ultimately, these findings characterize sleep loss as a metabolic disorder.

Metformin and Cognitive Performance in Patients With Type 2 Diabetes: An Umbrella Review

Contradictory results for the association between metformin intake and changes in cognitive function have been reported. We attempted to overview systematic reviews and meta-analyses showing the role of metformin, as mono or combination therapy, in cognitive performance alterations among patients with type 2 diabetes mellitus (T2DM) and to determine the quality of the evidence as well. To find the English-written reviews, a literature search was conducted on PubMed, Web of Science, Scopus, Cochrane Library, Trip, and Google Scholar by May 1, 2023. The literature search unearthed 2672 records, 10 of which were included in the study. Metformin may provide cognitive benefits for patients with type 2 diabetes, as evidence suggests potential improvements in memory and a reduced risk of neurodegenerative diseases. Even though the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) score alterations correspond to raising concerns about cognitive decline, Mini-Mental State Examination (MMSE) and selective reminding test (SRT) score improvements support metformin's role in improving specific cognitive domains. As such, metformin may exert differential impacts on various aspects of cognitive performance in these patients. However, the inconsistency and low quality of current evidence point toward the need for accurate research to elucidate whether metformin's cognitive effects are protective, neutral, or context-dependent based on patient profiles.

Acute Restraint Stress Induces Long-Lasting Synaptic Enhancement by Inhibiting AMPK Activation in AD Model Mice

BACKGROUND

Alzheimer's disease (AD) is characterized by a gradual synaptic loss. The progression of AD severely affects late-phase long-term potentiation (L-LTP), which is essential for long-term memory consolidation.

AIM

We have previously demonstrated the beneficial effects of acute restraint stress (ARS) on hippocampal LTP in AD mouse models. This study aimed to verify the effects and potential mechanisms of ARS on the maintenance of hippocampal L-LTP in two AD mouse models.

MATERIALS AND METHODS

5xFAD and Tg2576 mice underwent a 30-min body immobilization protocol to induce ARS, followed by electrophysiological recordings of L-LTP (> 3 h) in the CA1 region of thehippocampus.

RESULTS

The ARS-exposed group exhibited significantly enhanced L-LTP compared to the control group. Maintenance of L-LTP requires new protein synthesis and signaling via the mammalian target of rapamycin (mTOR) pathway. Our findings revealed that ARS increased hippocampal adenosine triphosphate (ATP) production and reduced AMPK activity. Inactivation of AMPK and subsequent activation of the mTOR pathway were strongly associated with the ARS-facilitated enhancement of L-LTP. Furthermore, our experiments using the mTOR inhibitor rapamycin demonstrated that it effectively prevented the enhancement of L-LTP following ARS, underscoring the pivotal role of mTOR in this process.

CONCLUSION

ARS may significantly modify AMPK activation and mTOR regulation in L-LTP, potentially triggering the mechanisms of long-term memory consolidation in AD mouse model mice. Identifying these underlying mechanisms could help promote the development of novel pharmaceutical agents for the treatment of AD.

How energy determines spatial localisation and copy number of molecules in neurons

In neurons, the quantities of mRNAs and proteins are traditionally assumed to be determined by functional, electrical or genetic factors. Yet, there may also be global, currently unknown computational rules that are valid across different molecular species inside a cell. Surprisingly, our results show that the energy for molecular turnover is a significant cellular expense, en par with spiking cost, and which requires energy-saving strategies. We show that the drive to save energy determines transcript quantities and their location while acting differently on each molecular species depending on the length, longevity and other features of the respective molecule. We combined our own data and experimental reports from five other large-scale mRNA and proteomics screens, comprising more than ten thousand molecular species to reveal the underlying computational principles of molecular localisation. We found that energy minimisation principles explain experimentally-reported exponential rank distributions of mRNA and protein copy numbers. Our results further reveal robust energy benefits when certain mRNA classes are moved into dendrites, for example mRNAs of proteins with long amino acid chains or mRNAs with large non-coding regions and long half-lives proving surprising insights at the level of molecular populations.

Interplay of epilepsy and long-term potentiation: implications for memory

The interplay between long-term potentiation (LTP) and epilepsy represents a crucial facet in understanding synaptic plasticity and memory within neuroscience. LTP, a phenomenon characterized by a sustained increase in synaptic strength, is pivotal in learning and memory processes, particularly in the hippocampus. This review delves into the intricate relationship between LTP and epilepsy, exploring how alterations in synaptic plasticity mechanisms akin to those seen in LTP contribute to the hyperexcitable state of epilepsy. This state is conceptualized as a dysregulation between LTP and LTD (Long-term depression), leading to pathologically enhanced synaptic efficacy. Additionally, the role of neuroinflammation in both LTP and epilepsy is examined, highlighting how inflammatory mediators can influence synaptic plasticity. The dual role of neuroinflammatory pathways, enhancing or inhibiting LTP, is a focal area of ongoing research. The significance of various signaling pathways, including the MAPK, mTOR, and WNT/β-catenin pathways, in the modulation of synaptic plasticity and their relevance in both LTP and epilepsy. These pathways are instrumental in memory formation, consolidation, and epileptogenesis, illustrating a complex interaction between cellular mechanisms in the nervous system. Lastly, the role of calcium signaling in the relationship between LTP and epilepsy is scrutinized. Aberrant calcium signaling in epilepsy leads to an enhanced, yet pathologically altered, LTP. This dysregulation disrupts normal neural pathways, potentially leading to cognitive dysfunction, particularly in memory encoding and retrieval. The review emphasizes the need for targeted interventions in epilepsy that address cognitive functions alongside seizure control.

Exploring the clinical connections between epilepsy and diabetes mellitus: Promising therapeutic strategies utilizing agmatine and metformin

PURPOSE

Diabetes mellitus (DM) and epilepsy and the psychological and socio-economic implications that are associated with their treatments can be quite perplexing. Metformin is an antihyperglycemic medication that is used to treat type 2 DM. In addition, metformin elicits protective actions against multiple diseases, including neurodegeneration and epilepsy. Recent studies indicate that metformin alters the resident gut microbiota in favor of species producing agmatine, an arginine metabolite which, in addition to beneficially altering metabolic pathways, is a potent neuroprotectant and neuromodulant.

METHODS

We first examine the literature for epidemiological and clinical evidences linking DM and epilepsy. Next, basing our analyses on published literature, we propose the possible complementarity of agmatine and metformin in the treatment of DM and epilepsy.

RESULTS

Our analyses of the clinical data suggest a significant association between pathogeneses of epilepsy and DM. Further, both agmatine and metformin appear to be multimodal therapeutic agents and have robust antiepileptogenic and antidiabetic properties. Data from animal and clinical studies largely support the use of metformin/agmatine as a double-edged pharmacotherapeutic agent against DM and epilepsy, particularly in their concurrent pathological occurrences.

CONCLUSION

The present review explores the evidences and available data on possible uses of metformin/agmatine as pertinent antidiabetic and antiepileptic agents. Our hope is that this will stimulate further research on the therapeutic actions of these multimodal agents, particularly for subject-specific clinical outcomes.

Metabolic Pathophysiology of Cortical Spreading Depression: A Review

Cortical spreading depression (CSD) is an electrophysiologic pathological state in which a wave of depolarization in the cerebral cortex is followed by the suppression of spontaneous neuronal activity. This transient spread of neuronal depolarization on the surface of the cortex is the hallmark of CSD. Numerous investigations have demonstrated that transmembrane ion transport, astrocytic ion clearing and fatigue, glucose metabolism, the presence of certain genetic markers, point mutations, and the expression of the enzyme responsible for the production of various arachidonic acid derivatives that participate in the inflammatory response, namely, cyclooxygenase (COX), all influence CSD. Here, we explore the associations between CSD occurrence in the cortex and various factors, including how CSD is related to migraines, how the glucose state affects CSD, the effect of TBI and its relationship with CSD and glucose metabolism, how different markers can be measured to determine the severity of CSD, and possible connections to oligemia, orexin, and leptin.

Reinforcement learning when your life depends on it: A neuro-economic theory of learning

Synaptic plasticity enables animals to adapt to their environment, but memory formation can require a substantial amount of metabolic energy, potentially impairing survival. Hence, a neuro-economic dilemma arises whether learning is a profitable investment or not, and the brain must therefore judiciously regulate learning. Indeed, in experiments it was observed that during starvation, Drosophila suppress formation of energy-intensive aversive memories. Here we include energy considerations in a reinforcement learning framework. Simulated flies learned to avoid noxious stimuli through synaptic plasticity in either the energy expensive long-term memory (LTM) pathway, or the decaying anesthesia-resistant memory (ARM) pathway. The objective of the flies is to maximize their lifespan, which is calculated with a hazard function. We find that strategies that switch between the LTM and ARM pathways, based on energy reserve and reward prediction error, prolong lifespan. Our study highlights the significance of energy-regulation of memory pathways and dopaminergic control for adaptive learning and survival. It might also benefit engineering applications of reinforcement learning under resources constraints.

Histamine H1-receptor-mediated modulation of NMDA receptors signaling responses

This study attempted to clarify the role of histamine H1 receptors in epilepsy by exploring the effects of agonists and inverse agonists on the rundown of the current induced by iterative applications of NMDA or GABA in primary neuronal culture. Mepyramine, a classical H1-receptor antagonist/inverse agonist, increased the NMDA current by about 40% during the first minutes of recording. This effect was concentration-dependent, maximal at 10 nM, and mimicked by triprolidine, another antagonist/inverse agonist. No endogenous histamine was detected in the cultures by a selective immunoassay; both compounds were acting as inverse agonists. Indicating a high constitutive activity of the H1 receptor in this system, histamine did not affect the NMDA rundown, including its settlement, but significantly reversed the effect of mepyramine. A similar pattern was obtained with 2,3 bromophenyl histamine, a selective H1-receptor agonist. The initial increase induced by the two inverse agonists was followed by the same rundown as in controls. H1- and NMDA receptors are colocalized in most cultured neuronal cells. Mepyramine and histamine did not affect the GABA rundown. Our findings suggest an interaction between H1- and NMDA receptors. Inactivation of the H1-receptor by its inverse agonists delays the settlement of the NMDA rundown, which may underlie their proconvulsant effect reported in clinics. Therefore, H1-receptor constitutive activity and the effect of histamine revealed in its absence, tend to facilitate the initiation of the rundown, which is consistent with the anticonvulsant properties of histamine via activation of H1-receptors reported in many studies.

Competitive plasticity to reduce the energetic costs of learning

The brain is not only constrained by energy needed to fuel computation, but it is also constrained by energy needed to form memories. Experiments have shown that learning simple conditioning tasks which might require only a few synaptic updates, already carries a significant metabolic cost. Yet, learning a task like MNIST to 95% accuracy appears to require at least 108 synaptic updates. Therefore the brain has likely evolved to be able to learn using as little energy as possible. We explored the energy required for learning in feedforward neural networks. Based on a parsimonious energy model, we propose two plasticity restricting algorithms that save energy: 1) only modify synapses with large updates, and 2) restrict plasticity to subsets of synapses that form a path through the network. In biology networks are often much larger than the task requires, yet vanilla backprop prescribes to update all synapses. In particular in this case, large savings can be achieved while only incurring a slightly worse learning time. Thus competitively restricting plasticity helps to save metabolic energy associated to synaptic plasticity. The results might lead to a better understanding of biological plasticity and a better match between artificial and biological learning. Moreover, the algorithms might benefit hardware because also electronic memory storage is energetically costly.

Adiponectin rescues synaptic plasticity in the dentate gyrus of a mouse model of Fragile X Syndrome

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and is the leading known single-gene cause of autism spectrum disorder. Patients with FXS display varied behavioural deficits that include mild to severe cognitive impairments in addition to mood disorders. Currently, there is no cure for this condition; however, there is an emerging focus on therapies that inhibit mechanistic target of rapamycin (mTOR)-dependent protein synthesis owing to the clinical effectiveness of metformin for alleviating some behavioural symptoms in FXS. Adiponectin (APN) is a neurohormone that is released by adipocytes and provides an alternative means to inhibit mTOR activation in the brain. In these studies, we show that Fmr1 knockout mice, like patients with FXS, show reduced levels of circulating APN and that both long-term potentiation (LTP) and long-term depression (LTD) in the dentate gyrus (DG) are impaired. Brief (20 min) incubation of hippocampal slices in APN (50 nM) was able to rescue both LTP and LTD in the DG and increased both the surface expression and phosphorylation of GluA1 receptors. These results provide evidence for reduced APN levels in FXS playing a role in decreasing bidirectional synaptic plasticity and show that therapies which enhance APN levels may have therapeutic potential for this and related conditions.This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Biophysical Modeling of Synaptic Plasticity

Dendritic spines are small, bulbous compartments that function as postsynaptic sites and undergo intense biochemical and biophysical activity. The role of the myriad signaling pathways that are implicated in synaptic plasticity is well studied. A recent abundance of quantitative experimental data has made the events associated with synaptic plasticity amenable to quantitative biophysical modeling. Spines are also fascinating biophysical computational units because spine geometry, signal transduction, and mechanics work in a complex feedback loop to tune synaptic plasticity. In this sense, ideas from modeling cell motility can inspire us to develop multiscale approaches for predictive modeling of synaptic plasticity. In this article, we review the key steps in postsynaptic plasticity with a specific focus on the impact of spine geometry on signaling, cytoskeleton rearrangement, and membrane mechanics. We summarize the main experimental observations and highlight how theory and computation can aid our understanding of these complex processes.

Energetically efficient learning in neuronal networks

Human and animal experiments have shown that acquiring and storing information can require substantial amounts of metabolic energy. However, computational models of neural plasticity only seldom take this cost into account, and might thereby miss an important constraint on biological learning. This review explores various ways to reduce energy requirements for learning in neural networks. By comparing the resulting learning rules to cognitive and neurophysiological observations, we discuss how energy efficiency might have shaped biological learning.

Influence of metabolic stress and metformin on synaptic protein profile in SH-SY5Y-derived neurons

Insulin resistance (IR) is associated with reductions in neuronal proteins often observed with Alzheimer's disease (AD), however, the mechanisms through which IR promotes neurodegeneration/AD pathogenesis are poorly understood. Metformin (MET), a potent activator of the metabolic regulator AMPK is used to treat IR but its effectiveness for AD is unclear. We have previously shown that chronic AMPK activation impairs neurite growth and protein synthesis in SH-SY5Y neurons, however, AMPK activation in IR was not explored. Therefore, we examined the effects of MET-driven AMPK activation with and without IR. Retinoic acid-differentiated SH-SY5Y neurons were treated with: (1) Ctl: 24 h vehicle followed by 24 h Vehicle; (2) HI: 100 nM insulin (24 h HI followed by 24 h HI); or (3) MET: 24 h vehicle followed by 24 h 2 mM metformin; (4) HI/MET: 24 h 100 nM insulin followed by 24 h 100 nM INS+2 mM MET. INS and INS/MET groups saw impairments in markers of insulin signaling (Akt S473, mTOR S2448, p70s6k T389, and IRS-1S636) demonstrating IR was not recovered with MET treatment. All treatment groups showed reductions in neuronal markers (post-synaptic marker HOMER1 mRNA content and synapse marker synaptophysin protein content). INS and MET treatments showed a reduction in the content of the mature neuronal marker NeuN that was prevented by INS/MET. Similarly, increases in cell size/area, neurite length/area observed with INS and MET, were prevented with INS/MET. These findings indicate that IR and MET impair neuronal markers through distinct pathways and suggest that MET is ineffective in treating IR-driven impairments in neurons.

Autophagy and autophagy signaling in Epilepsy: possible role of autophagy activator

Autophagy is an explicit cellular process to deliver dissimilar cytoplasmic misfolded proteins, lipids and damaged organelles to the lysosomes for degradation and elimination. The mechanistic target of rapamycin (mTOR) is the main negative regulator of autophagy. The mTOR pathway is involved in regulating neurogenesis, synaptic plasticity, neuronal development and excitability. Exaggerated mTOR activity is associated with the development of temporal lobe epilepsy, genetic and acquired epilepsy, and experimental epilepsy. In particular, mTOR complex 1 (mTORC1) is mainly involved in epileptogenesis. The investigation of autophagy's involvement in epilepsy has recently been conducted, focusing on the critical role of rapamycin, an autophagy inducer, in reducing the severity of induced seizures in animal model studies. The induction of autophagy could be an innovative therapeutic strategy in managing epilepsy. Despite the protective role of autophagy against epileptogenesis and epilepsy, its role in status epilepticus (SE) is perplexing and might be beneficial or detrimental. Therefore, the present review aims to revise the possible role of autophagy in epilepsy.

The Role of circTmeff-1 in Morphine Addiction Memory of Mice

In addition to the essential pharmacological effects of opioids, situational cues associated with drug addiction memory are key triggers for drug seeking. CircRNAs, an emerging hotspot regulator in crown genetics, play an important role in central nervous system-related diseases. However, the internal mediating mechanism of circRNAs in the field of drug reward and addiction memory remains unknown. Here, we trained mice on a conditional place preference (CPP) model and collected nucleus accumbens (NAc) tissues from day 1 (T0) and day 8 (T1) for high-throughput RNA sequencing. QRT-PCR analysis revealed that circTmeff-1 was highly expressed in the NAc core but not in the NAc shell, suggesting that it plays a role in addiction memory formation. Meanwhile, the down-regulation of circTmeff-1 by adeno-associated viruses in the NAc core or shell could inhibit the morphine CPP scores. Subsequently, the GO and KEGG analyses indicated that circTmeff-1 might regulate the addiction memory via the MAPK and AMPK pathways. These findings suggest that circTmeff-1 in NAc plays a crucial role in morphine-dependent memory formation.

Computational modeling of AMPK and mTOR crosstalk in glutamatergic synapse calcium signaling

Neuronal energy consumption is vital for information processing and memory formation in synapses. The brain consists of just 2% of the human body's mass, but consumes almost 20% of the body's energy budget. Most of this energy is attributed to active transport in ion signaling, with calcium being the canonical second messenger of synaptic transmission. Here, we develop a computational model of synaptic signaling resulting in the activation of two protein kinases critical in metabolic regulation and cell fate, AMP-Activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) and investigate the effect of glutamate stimulus frequency on their dynamics. Our model predicts that frequencies of glutamate stimulus over 10 Hz perturb AMPK and mTOR oscillations at higher magnitudes by up to 36% and change the area under curve (AUC) by 5%. This dynamic difference in AMPK and mTOR activation trajectories potentially differentiates high frequency stimulus bursts from basal neuronal signaling leading to a downstream change in synaptic plasticity. Further, we also investigate the crosstalk between insulin receptor and calcium signaling on AMPK and mTOR activation and predict that the pathways demonstrate multistability dependent on strength of insulin signaling and metabolic consumption rate. Our predictions have implications for improving our understanding of neuronal metabolism, synaptic pruning, and synaptic plasticity.

Portulaca oleracea L. (purslane) improves the anti-inflammatory, antioxidant and autophagic actions of metformin in the hippocampus of diabetic demented rats

Great body of evidence links cognitive decline to diabetes/insulin resistance. In this study the effect of Portulaca oleracea (PUR) (100 mg/kg), Metformin (MET) (200 mg/kg), a first line diabetes mellitus type 2 therapy, and their combination on cognitive function and hippocampal markers in diabetic rats were assessed. Male rats were injected with streptozotocin (30 mg/kg on two successive weeks) followed by 4 weeks of treatment. Possible antioxidant, anti-inflammatory, and autophagy enhancing mechanisms of these drugs were investigated in the hippocampal tissue using spectrophotometry, ELISA, and western blotting. Diabetic rats suffered significant cognitive impairment in Morris's water maze, hippocampal TBARS elevation, GSH depletion, and SOD upregulation. In addition, diabetes promoted the secretion of hippocampal inflammatory cytokines, TNF-α and IL-1β, and depleted anti-inflammatory cytokines as IL-10. Such detrimental changes were reversed by MET and/or PUR. Notably, AMPK was upregulated by diabetes, then restored to normal by MET and/or PUR. The pattern of change in AMPK expression was concomitant with changes in oxidative and inflammatory burden. Hence, AMPK is believed to be a key mediator in most of the measured pre-AD markers in this study. However, from our results, PUR is believed to have non-AMPK dependent actions as well. In conclusion, antidiabetic agents as metformin and purslane extract proved to be invaluable in addressing the cognitive decline and hippocampal changes that arise as a complication of diabetes. They mainly acted through AMPK pathway; however, their usefulness was not limited to AMPK pathways since their combination was suggested to have a different mechanism.

Metformin alleviates neurocognitive impairment in aging via activation of AMPK/BDNF/PI3K pathway

Slowing down age-related neurocognitive impairment has been a challenge. We evaluated the therapeutic effects of metformin in D-galactose-induced aging. Additionally, we studied the potential molecular mechanisms that could be responsible for metformin's anti-aging effects. Thirty male rats were equally divided into: 1-control group, which received saline solution, 2-D-galactose (D-gal) group, which received D-galactose (100 mg/kg/day) by gastric lavage for eight weeks, and 3-D-galactose + Metformin (D-gal + Met) treated group, which received D-galactose + metformin (200 mg/kg/day) by gastric lavage for eight weeks. Neurocognitive assessment was done. Measurement of inflammatory, oxidative stress, and BDNF biomarkers was performed. AMPK and PI3K genes expression were assessed. Hippocampal tissues were dissected for histopathological and immunohistochemical studies. D-gal resulted in neurocognitive impairments, elevation of inflammatory biomarkers, altered oxidative stress markers, decreased BDNF, decreased expression of synaptophysin and Bcl2 with increased expression of Caspase-3, and down-regulation of AMPK and PI3K genes. Neurodegenerative changes were present in the hippocampus. Metformin restored significantly D-gal induced neurodegenerative changes. We concluded that metformin could alleviate age-induced neurocognitive deficit via amelioration of neuroinflammation, attenuation of oxidative stress, reduction of apoptosis, as well as promotion of synaptic plasticity. These mechanisms could be mediated via the activation of the AMPK/BDNF/PI3K pathway.

Chronic AMPK Activation Reduces the Expression and Alters Distribution of Synaptic Proteins in Neuronal SH-SY5Y Cells

Neuronal growth and synaptic function are dependent on precise protein production and turnover at the synapse. AMPK-activated protein kinase (AMPK) represents a metabolic node involved in energy sensing and in regulating synaptic protein homeostasis. However, there is ambiguity surrounding the role of AMPK in regulating neuronal growth and health. This study examined the effect of chronic AMPK activation on markers of synaptic function and growth. Retinoic-acid-differentiated SH-SY5Y human neuroblastoma cells were treated with A-769662 (100 nM) or Compound C (30 nM) for 1, 3, or 5 days before AMPK, mTORC1, and markers for synapse function were examined. Cell morphology, neuronal marker content, and location were quantified after 5 days of treatment. AMPK phosphorylation was maintained throughout all 5 days of treatment with A-769662 and resulted in chronic mTORC1 inhibition. Lower total, soma, and neuritic neuronal marker contents were observed following 5 d of AMPK activation. Neurite protein abundance and distribution was lower following 5 days of A-769662 treatment. Our data suggest that chronic AMPK activation impacts synaptic protein content and reduces neurite protein abundance and distribution. These results highlight a distinct role that metabolism plays on markers of synapse health and function.

The neuropeptide VIP potentiates intestinal innate type 2 and type 3 immunity in response to feeding

The nervous system and the immune system both rely on an extensive set of modalities to perceive and act on perturbations in the internal and external environments. During feeding, the intestine is exposed to nutrients that may contain noxious substances and pathogens. Here we show that Vasoactive Intestinal Peptide (VIP), produced by the nervous system in response to feeding, potentiates the production of effector cytokines by intestinal type 2 and type 3 innate lymphoid cells (ILC2s and ILC3s). Exposure to VIP alone leads to modest activation of ILCs, but strongly potentiates ILCs to concomitant or subsequent activation by the inducer cytokines IL-33 or IL-23, via mobilization of cAMP and energy by glycolysis. Consequently, VIP increases resistance to intestinal infection by the helminth Trichuris muris and the enterobacteria Citrobacter rodentium. These findings uncover a functional neuro-immune crosstalk unfolding during feeding that increases the reactivity of innate immunity necessary to face potential threats associated with food intake.

Central Adiponectin Signaling – A Metabolic Regulator in Support of Brain Plasticity

Brain plasticity and metabolism are tightly connected by a constant influx of peripheral glucose to the central nervous system in order to meet the high metabolic demands imposed by neuronal activity. Metabolic disturbances highly affect neuronal plasticity, which underlies the prevalent comorbidity between metabolic disorders, cognitive impairment, and mood dysfunction. Effective pro-cognitive and neuropsychiatric interventions, therefore, should consider the metabolic aspect of brain plasticity to achieve high effectiveness. The adipocyte-secreted hormone, adiponectin, is a metabolic regulator that crosses the blood-brain barrier and modulates neuronal activity in several brain regions, where it exerts neurotrophic and neuroprotective properties. Moreover, adiponectin has been shown to improve neuronal metabolism in different animal models, including obesity, diabetes, and Alzheimer’s disease. Here, we aim at linking the adiponectin’s neurotrophic and neuroprotective properties with its main role as a metabolic regulator and to summarize the possible mechanisms of action on improving brain plasticity via its role in regulating the intracellular energetic activity. Such properties suggest adiponectin signaling as a potential target to counteract the central metabolic disturbances and impaired neuronal plasticity underlying many neuropsychiatric disorders.

Butyric Acid Precursor Tributyrin Modulates Hippocampal Synaptic Plasticity and Prevents Spatial Memory Deficits: Role of PPARγ and AMPK

BACKGROUND

Short chain fatty acids (SCFA), such as butyric acid (BA), derived from the intestinal fermentation of dietary fiber and contained in dairy products, are gaining interest in relation to their possible beneficial effects on neuropsychological disorders.

METHODS

C57BL/6J male mice were used to investigate the effect of tributyrin (TB), a prodrug of BA, on hippocampus (HIP)-dependent spatial memory, HIP synaptic transmission and plasticity mechanisms, and the expression of genes and proteins relevant to HIP glutamatergic transmission.

RESULTS

Ex vivo studies, carried out in HIP slices, revealed that TB can transform early-LTP into late-LTP (l-LTP) and to rescue LTP-inhibition induced by scopolamine. The facilitation of l-LTP induced by TB was blocked both by GW9662 (a PPARγ antagonist) and C-Compound (an AMPK inhibitor), suggesting the involvement of both PPARγ and AMPK on TB effects. Moreover, 48-hour intake of a diet containing 1% TB prevented, in adolescent but not in adult mice, scopolamine-induced impairment of HIP-dependent spatial memory. In the adolescent HIP, TB upregulated gene expression levels of Pparg, leptin, and adiponectin receptors, and that of the glutamate receptor subunits AMPA-2, NMDA-1, NMDA-2A, and NMDA-2B.

CONCLUSIONS

Our study shows that TB has a positive influence on LTP and HIP-dependent spatial memory, which suggests that BA may have beneficial effects on memory.

Characterization of Early Alzheimer's Disease-Like Pathological Alterations in Non-Human Primates with Aging: A Pilot Study

BACKGROUND

Sporadic or late onset Alzheimer's disease (LOAD) is a multifactorial neurodegenerative disease with aging the most known risk factor. Non-human primates (NHPs) may serve as an excellent model to study LOAD because of their close similarity to humans in many aspects including neuroanatomy and neurodevelopment. Recent studies reveal AD-like pathology in old NHPs.

OBJECTIVE

In this pilot study, we took advantage of brain samples from 6 Cynomolgus macaques that were divided into two groups: middle aged (average age 14.81 years) and older (average age 19.33 years). We investigated whether AD-like brain pathologies are present in the NHPs.

METHODS

We used immunohistochemical method to examine brain Aβ pathology and neuron density. We applied biochemical assays to measure tau phosphorylation and multiple signaling pathways indicated in AD. We performed electron microscopy experiments to study alterations of postsynaptic density and mitochondrial morphology in the brain of NHPs.

RESULTS

We found multiple AD-like pathological alteration in the prefrontal cortex (but not in the hippocampus) of the older NHPs including tau hyperphosphorylation, increased activity of AMP-activated protein kinase (AMPK), decreased expression of protein phosphatase 2A (PP2A), impairments in mitochondrial morphology, and postsynaptic densities formation.

CONCLUSION

These findings may provide insights into the factors contributing to the development of LOAD, particularly during the early stage transitioning from middle to old age. Future endeavors are warranted to elucidate mechanisms underlying the regional (and perhaps cellular) vulnerability with aging and the functional correlation of such pathological changes in NHPs.

Pretreatment with metformin prevents microcystin-LR-induced tau hyperphosphorylation via mTOR-dependent PP2A and GSK-3β activation

Microcystin-leucine-arginine (MC-LR) is a toxin secreted by freshwater cyanobacteria that is considered a potential environmental risk factor for Alzheimer's disease (AD). A previous study indicated that tau protein hyperphosphorylation via protein phosphatase 2A (PP2A) and GSK-3β inhibition was the mechanism by which MC-LR induces neurotoxicity; however, how MC-LR-induced neurotoxicity can be effectively prevented remains unclear. In this study, the reversal effect of metformin on MC-LR-induced neurotoxicity was investigated. The results showed that metformin effectively prevented tau hyperphosphorylation at Ser202 caused by MC-LR through PP2A and GSK-3b activity. The effect of metformin on PP2A activity was dependent on the inhibition of mTOR in MC-LR-treated SH-SY5Y cells. Metformin prevented spatial memory deficits in rats caused by intrahippocampal MC-LR administration. In sum, the results suggested that metformin can ameliorate the MC-LR-induced AD-like phenotype by preventing tau phosphorylation at Ser202, which was mainly mediated by mTOR-dependent PP2A and GSK-3β activation.

Isoform-specific dysregulation of AMP-activated protein kinase signaling in a non-human primate model of Alzheimer's disease

AMP-activated protein kinase (AMPK) is a molecular sensor that is critical for the maintenance of cellular energy homeostasis, disruption of which has been indicated in multiple neurodegenerative diseases including Alzheimer's disease (AD). Mammalian AMPK is a heterotrimeric complex and its enzymatic α subunit exists in two isoforms: AMPKα1 and AMPKα2. Here we took advantage of a recently characterized non-human primate (NHP) model with sporadic AD-like neuropathology to explore potential relationships between AMPK signaling and AD-like neuropathology. Subjects were nine female vervet monkeys aged 19.5 to 23.4 years old. Subjects were classified into three groups, control lacking AD pathology (n = 3), moderate AD pathology (n = 3), and more severe AD Pathology (n = 3). We found increased activity (assessed by phosphorylation) of AMPKα2 in hippocampi of NHP with AD-like neuropathology, compared to the subjects without AD pathology, with no alterations of AMPKα1 activity. Across all subjects, CSF Abeta42 was inversely associated with cerebral amyloid plaque density. Further, Aβ plaque burden is correlated with levels of either soluble or insoluble brain Aβ measurement. Unbiased mass spectrometry based proteomics studies combined with bioinformatics analysis revealed that many of the dysregulated proteins characteristic of AD neuropathology are associated with AMPK signaling. Our findings on the AMPK molecular signaling cascades provide further support for use of the NHP model to investigate new therapeutic strategies and development of novel biomarkers for Alzheimer's disease.

Evaluation of the effects of metformin as adenosine monophosphate-activated protein kinase activator on spatial learning and memory in a rat model of multiple sclerosis disease

In patients with multiple sclerosis (MS) disease, cognitive deficits have been detected because of destruction of hippocampus. Cognitive impairment is one of the common signs in MS. Recent studies showed that metformin (Met) has wide-ranging effects in the treatment of diseases. Here, we have tried to study the preservative effects of Met as adenosine monophosphate-activated protein kinase (AMPK) activator on the hippocampus dentate gyrus (DG) neuronal firing pattern, motor coordination, and learning & memory loss following MS induction. The MS induction was done by local ethidium bromide (EB) injection into the rat hippocampus. Then, rats were treated with Met (200 mg/kg) for two weeks. Spatial memory and learning status were assessed using Morris water maze. A neuronal single-unit recording was measured from hippocampus DG. After decapitation, the bilateral hippocampi separated to measure malondialdehyde (MDA). Treatment with Met ameliorated latency times and path lengths (P < 0.05, P < 0.01, P < 0.001 in 1th, 2th, 3th and 4th days) in the Met + MS group respectively. The percent of total time spent in goal quarter and the average number of spikes/bin were decreased significantly in MS rats compared with the sham group (p < 0.001) but significantly increased in the metformin-treated MS group (Met + MS), (p < 0.01, p < 0.001). Met treatment in rats with MS significantly reduced the concentration of MDA, which is an indicator of lipid peroxidation compared to untreated groups. These observations show that increase of neuronal activity, sensory-motor coordination, and improvement of spatial memory in MS rats treated with Met appears via an increment of AMPK.

The functions of repressor element 1-silencing transcription factor in models of epileptogenesis and post-ischemia

Epilepsy is a debilitating neurological disorder characterised by recurrent seizures for which 30% of patients are refractory to current treatments. The genetic and molecular aetiologies behind epilepsy are under investigation with the goal of developing new epilepsy medications. The transcriptional repressor REST (Repressor Element 1-Silencing Transcription factor) is a focus of interest as it is consistently upregulated in epilepsy patients and following brain insult in animal models of epilepsy and ischemia. This review analyses data from different epilepsy models and discusses the contribution of REST to epileptogenesis. We propose that in healthy brains REST acts in a protective manner to homeostatically downregulate increases in excitability, to protect against seizure through downregulation of BDNF (Brain-Derived Neurotrophic Factor) and its receptor, TrkB (Tropomyosin receptor kinase B). However, in epilepsy patients and post-seizure, REST may increase to a larger degree, which allows downregulation of the glutamate receptor subunit GluR2. This leads to AMPA glutamate receptors lacking GluR2 subunits, which have increased permeability to Ca²⁺, causing excitotoxicity, cell death and seizure. This concept highlights therapeutic potential of REST modulation through gene therapy in epilepsy patients.

Spatiotemporal Regulation of Transcript Isoform Expression in the Hippocampus

Proper development and plasticity of hippocampal neurons require specific RNA isoforms to be expressed in the right place at the right time. Precise spatiotemporal transcript regulation requires the incorporation of essential regulatory RNA sequences into expressed isoforms. In this review, we describe several RNA processing strategies utilized by hippocampal neurons to regulate the spatiotemporal expression of genes critical to development and plasticity. The works described here demonstrate how the hippocampus is an ideal investigative model for uncovering alternate isoform-specific mechanisms that restrict the expression of transcripts in space and time.

Mammalian/mechanistic target of rapamycin (mTOR) complexes in neurodegeneration

Novel targets to arrest neurodegeneration in several dementing conditions involving misfolded protein accumulations may be found in the diverse signaling pathways of the Mammalian/mechanistic target of rapamycin (mTOR). As a nutrient sensor, mTOR has important homeostatic functions to regulate energy metabolism and support neuronal growth and plasticity. However, in Alzheimer's disease (AD), mTOR alternately plays important pathogenic roles by inhibiting both insulin signaling and autophagic removal of β-amyloid (Aβ) and phospho-tau (ptau) aggregates. It also plays a role in the cerebrovascular dysfunction of AD. mTOR is a serine/threonine kinase residing at the core in either of two multiprotein complexes termed mTORC1 and mTORC2. Recent data suggest that their balanced actions also have implications for Parkinson's disease (PD) and Huntington's disease (HD), Frontotemporal dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS). Beyond rapamycin; an mTOR inhibitor, there are rapalogs having greater tolerability and micro delivery modes, that hold promise in arresting these age dependent conditions.

Brain-specific suppression of AMPKα2 isoform impairs cognition and hippocampal LTP by PERK-mediated eIF2α phosphorylation

The AMP-activated protein kinase (AMPK) is a molecular sensor to maintain energy homeostasis. The two isoforms of the AMPK catalytic subunit (AMPKα1 and α2) are both expressed in brains, but their roles in cognition are unknown. We generated conditional knockout mice in which brain AMPKα isoforms are selectively suppressed (AMPKα1/α2 cKO), and determined the isoform-specific effects in mice of either sex on cognition and synaptic plasticity. AMPKα2 cKO but not AMPKα1 cKO displayed impaired cognition and hippocampal late long-term potentiation (L-LTP). Further, AMPKα2 cKO mice exhibited decreased dendritic spine density and abnormal spine morphology in hippocampus. Electron microscope imaging demonstrated reduced postsynaptic density formation and fewer dendritic polyribosomes in hippocampi of AMPKα2 cKO mice. Biochemical studies revealed unexpected findings that repression of AMPKα2 resulted in increased phosphorylation of mRNA translational factor eIF2α and its kinase PERK. Importantly, L-LTP failure and cognitive impairments displayed in AMPKα2 cKO mice were alleviated by suppressing PERK activity pharmacologically or genetically. In summary, we demonstrate here that brain-specific suppression of AMPKα2 isoform impairs cognition and hippocampal LTP by PERK-mediated eIF2α phosphorylation, providing molecular mechanisms linking metabolism, protein synthesis, and cognition.

Integrated transcriptome and metabolome analysis reveals molecular responses of the clams to acute hypoxia

Mudflat shellfish have evolved well-adapted strategies for coping with dynamic environmental fluxes and stressful conditions, including oxygen availability. The Manila clams Ruditapes philippinarum are worldwide cultured shellfish in marine intertidal zone, which usually encounter great risk of acute hypoxia exposure in coastal habitats. To reveal the effects of acute hypoxia on metabolic changes of the clams, we performed the integrated analysis of transcriptomics and metabolomics to investigate the global changes of genes and metabolites during acute hypoxia stress at the whole-organism level. The comparative transcriptome analysis reveals that the clams show the remarkable depression in a variety of biological performance, such as metabolic rates, neuronal activity, biomineralization activity, and cell proliferation and differentiation at the hypoxic condition. The metabolomic analysis reveals that amino acid metabolism plays a critical role in the metabolic changes of the clams in response to acute hypoxia. A variety of free amino acids may not only be served as the potential osmolytes for osmotic regulation, but also may contribute to energy production during the acute hypoxia exposure. The metabolite analysis also reveals several important biomarkers for metabolic changes, and provides new insights into how clams deal with acute hypoxia. These findings suggest that clams may get through acute hypoxia stress by the adaptive metabolic strategy to survive short-period of acute hypoxia which is likely to occur in their typical habitat. The present findings will not only shed lights on the molecular and metabolic mechanisms of adaptive strategies under stressful conditions, but also provide the signaling metabolites to assess the physiological states of clams in aquaculture.

Resveratrol, Metabolic Dysregulation, and Alzheimer's Disease: Considerations for Neurogenerative Disease

Alzheimer’s disease (AD) has traditionally been discussed as a disease where serious cognitive decline is a result of Aβ-plaque accumulation, tau tangle formation, and neurodegeneration. Recently, it has been shown that metabolic dysregulation observed with insulin resistance and type-2 diabetes actively contributes to the progression of AD. One of the pathologies linking metabolic disease to AD is the release of inflammatory cytokines that contribute to the development of brain neuroinflammation and mitochondrial dysfunction, ultimately resulting in amyloid-beta peptide production and accumulation. Improving these metabolic impairments has been shown to be effective at reducing AD progression and improving cognitive function. The polyphenol resveratrol (RSV) improves peripheral metabolic disorders and may provide similar benefits centrally in the brain. RSV reduces inflammatory cytokine release, improves mitochondrial energetic function, and improves Aβ-peptide clearance by activating SIRT1 and AMPK. RSV has also been linked to improved cognitive function; however, the mechanisms of action are less defined. However, there is evidence to suggest that chronic RSV-driven AMPK activation may be detrimental to synaptic function and growth, which would directly impact cognition. This review will discuss the benefits and adverse effects of RSV on the brain, highlighting the major signaling pathways and some of the gaps surrounding the use of RSV as a treatment for AD.

Energy sensors in drug addiction: A potential therapeutic target

Addiction is defined as the repeated exposure and compulsive seek of psychotropic drugs that, despite the harmful effects, generate relapse after the abstinence period. The psychophysiological processes associated with drug addiction (acquisition/expression, withdrawal, and relapse) imply important alterations in neurotransmission and changes in presynaptic and postsynaptic plasticity and cellular structure (neuroadaptations) in neurons of the reward circuits (dopaminergic neuronal activity) and other corticolimbic regions. These neuroadaptation mechanisms imply important changes in neuronal energy balance and protein synthesis machinery. Scientific literature links drug-induced stimulation of dopaminergic and glutamatergic pathways along with presence of neurotrophic factors with alterations in synaptic plasticity and membrane excitability driven by metabolic sensors. Here, we provide current knowledge of the role of molecular targets that constitute true metabolic/energy sensors such as AMPK, mTOR, ERK, or K_ATP in the development of the different phases of addiction standing out the main brain regions (ventral tegmental area, nucleus accumbens, hippocampus, and amygdala) constituting the hubs in the development of addiction. Because the available treatments show very limited effectiveness, evaluating the drug efficacy of AMPK and mTOR specific modulators opens up the possibility of testing novel pharmacotherapies for an individualized approach in drug abuse.

Sprinkler Technology Improves Broiler Production Sustainability: From Stress Alleviation to Water Usage Conservation: A Mini Review

Global poultry production is facing several challenges including a projected increase in global demand for high quality animal proteins and the need to adapt to environmental contrasts including heat stress and the increasing pressure on natural resource (water, land, and energy) availability. Heat stress is one of the most challenging stressor to poultry production because of its strong adverse effects on welfare, production, mortality, and water usage. Most commercial poultry houses worldwide are equipped with a combination of tunnel ventilation and evaporative cooling system (pads, fogging, or low-pressure misting systems) as the status quo to overcome heat stress. Despite prior investments in these systems, critical problems continue to impede poultry production efficiency, which still declines during hot seasons. In fact, these systems tend to saturate the barn air with moisture (>70% relative humidity) which is counterproductive to the bird's own physiological ability to cool itself by hyperventilation (evaporative heat loss). The second challenge with these systems is the significant amount of water usage. This review will summarize some of the benefits of surface wetting of birds through sprinkler technology (SPRINK) that has higher efficiency to maintain birds' comfort with significantly less use of cooling water. Despite higher air temperature and lower relative humidity in the sprinkler house, the SPRINK decreased broiler body core temperature, reduced systemic and intracellular stress, preserved intracellular energy, and averaged six points better FCR compared to evaporative cooling system.

The return of malonyl-CoA to the brain: Cognition and other stories

Nutrients, hormones and the energy sensor AMP-activated protein kinase (AMPK) tightly regulate the intracellular levels of the metabolic intermediary malonyl-CoA, which is a precursor of fatty acid synthesis and a negative regulator of fatty acid oxidation. In the brain, the involvement of malonyl-CoA in the control of food intake and energy homeostasis has been known for decades. However, recent data uncover a new role in cognition and brain development. The sensing of malonyl-CoA by carnitine palmitoyltransferase 1 (CPT1) proteins regulates a variety of functions, such as the fate of neuronal stem cell precursors, the motility of lysosomes in developing axons, the trafficking of glutamate receptors to the neuron surface (necessary for proper synaptic function) and the metabolic coupling between astrocytes and neurons. We discuss the relevance of those recent findings evidencing how nutrients and metabolic disorders impact cognition. We also enumerate all nutritional and hormonal conditions that are known to regulate malonyl-CoA levels in the brain, reflect on protein malonylation as a new post-translational modification, and give a reasoned vision of the opportunities and challenges that future research in the field could address.

Caloric Restriction and Ketogenic Diet Therapy for Epilepsy: A Molecular Approach Involving Wnt Pathway and KATP Channels

Epilepsy is a neurological disorder in which, in many cases, there is poor pharmacological control of seizures. Nevertheless, it may respond beneficially to alternative treatments such as dietary therapy, like the ketogenic diet or caloric restriction. One of the mechanisms of these diets is to produce a hyperpolarization mediated by the adenosine triphosphate (ATP)-sensitive potassium (KATP) channels (KATP channels). An extracellular increase of K+ prevents the release of Ca2+ by inhibiting the signaling of the Wnt pathway and the translocation of β-catenin to the cell nucleus. Wnt ligands hyperpolarize the cells by activating K+ current by Ca2+. Each of the diets described in this paper has in common a lower use of carbohydrates, which leads to biochemical, genetic processes presumed to be involved in the reduction of epileptic seizures. Currently, there is not much information about the genetic processes implicated as well as the possible beneficial effects of diet therapy on epilepsy. In this review, we aim to describe some of the possible genes involved in Wnt pathways, their regulation through the KATP channels which are implicated in each one of the diets, and how they can reduce epileptic seizures at the molecular level.

Resveratrol and Metformin Recover Prefrontal Cortex AMPK Activation in Diet-Induced Obese Mice but Reduce BDNF and Synaptophysin Protein Content

BACKGROUND

Obesity, insulin resistance, and type 2 diabetes are established risk factors for the development of Alzheimer's disease (AD). Given this connection, two drugs, metformin (MET) and resveratrol (RESV), are considered for the clearance of amyloid-β peptides through AMPK-mediated activation of autophagy. However, overactivation of AMPK observed in late-stage AD brains and relationships between AMPK and neurogenesis (through mTORC1 inhibition), questions treatment with these drugs.

OBJECTIVE

To examine if MET and/or RESV supplementation activates brain AMPK, regulates markers of autophagy, and affects markers of neuronal health/neurogenesis.

METHODS

8-week-old male C57BL/6J mice were fed a low (N = 12; 10% kcal fat; LFD) or high fat diet (N = 40; 60% kcal fat; HFD) for 9 weeks to induce insulin resistance and obesity. HFD mice were then treated with/without MET (250 mg/kg/day), RESV (100 mg/kg/day), or COMBO (MET: 250 mg/kg/day, RESV: 100 mg/kg/day) for 5 weeks. Hippocampus and prefrontal cortex were extracted for western blotting analysis.

RESULTS

Cortex AMPK (T172) and raptor (S792, the regulatory subunit of mTORC1) phosphorylation were upregulated following RESV, COMBO treatments. mTOR (S2448) and ULK1 (S555) activation was seen following MET, COMBO and RESV, COMBO treatments, respectively, in the cortex and hippocampus. p62 content was decreased following RESV, COMBO, with LC3 content being increased following RESV treatment in the cortex. Brain derived neurotropic factor (BDNF) was significantly decreased following RESV, COMBO, and synaptophysin following all treatment in the cortex.

CONCLUSION

These results demonstrate that while treatments upregulated markers of autophagy in the prefrontal cortex, reductions in neuronal health markers question the efficacy of AMPK as a therapy for AD.

Persistent changes in extracellular lactate dynamics following synaptic potentiation

A diverse array of neurometabolic coupling mechanisms exist within the brain to ensure that sufficient metabolite availability is present to meet both acute and chronic energetic demands. Excitatory synaptic activity, which produces the majority of the brain's energetic demands, triggers a rapid metabolic response including a characteristic shift towards aerobic glycolysis. Herein, astrocytically derived lactate appears to serve as an important metabolite to meet the extensive metabolic needs of activated neurons. Despite a wealth of literature characterizing lactate's role in mediating these acute metabolic needs, the extent to which lactate supports chronic energetic demands of neurons remains unclear. We hypothesized that synaptic potentiation, a ubiquitous brain phenomenon that can produce chronic alterations in synaptic activity, could necessitate persistent alterations in brain energetics. In freely-behaving rats, we induced long-term potentiation (LTP) of synapses within the dentate gyrus through high-frequency electrical stimulation (HFS) of the medial perforant pathway. Before, during, and after LTP induction, we continuously recorded extracellular lactate concentrations within the dentate gyrus to assess how changes in synaptic strength alter local glycolytic activity. Synaptic potentiation 1) altered the acute response of extracellular lactate to transient neuronal activation as evident by a larger initial dip and subsequent overshoot and 2) chronically increased local lactate availability. Although synapses were potentiated immediately following HFS, observed changes in lactate dynamics were only evident beginning ~24 h later. Once observed, however, both synaptic potentiation and altered lactate dynamics persisted for the duration of the experiment (~72 h). Persistent alterations in synaptic strength, therefore, appear to be associated with metabolic plasticity in the form of persistent augmentation of glycolytic activity.

Evaluation of the ameliorative effects of oral administration of metformin on epileptogenesis in the temporal lobe epilepsy model in rats

AIMS

Understanding the underlying molecular mechanisms involved in epileptogenesis is necessary to target the best therapeutic interventions in epilepsy. Recently, it has been postulated that metformin, an old antidiabetic oral drug, has anti-seizure properties mostly due to its antioxidant activities. This study was designed to evaluate the ameliorative effects of metformin on the progression of epilepsy in the temporal lobe epilepsy model in rats.

MAIN METHODS

Temporal lobe Epilepsy was induced by intracerebroventricular microinjection of kainic acid. Metformin was orally administered for two weeks before induction of epilepsy. Anti-epileptogenic activity of metformin was evaluated by intracranial electroencepholography (IEEG) recording to detect spontaneous seizures, mossy fiber sprouting by Timm staining, neurogenesis by BrdU staining.

KEY FINDINGS

Oral administration of metformin prior to kainite-induced status epilepticus blocked the variant characterizations of epileptogenesis like neuronal cell death, aberrant neurogenesis, mossy fiber sprouting, and spontaneous seizures.

SIGNIFICANCE

These findings indicate that metformin has potential anti-epileptogenic properties in temporal lobe epilepsy.

Therapeutic Potential of AMP-Activated Protein Kinase in Alzheimer's Disease

Currently there is no cure or effective disease-modifying therapy for Alzheimer's disease (AD), the most common form of dementia that is becoming a global threat to public health. It is important to develop novel therapeutic strategies targeting AD pathophysiology particularly synaptic failure and cognitive impairments. Recent studies revealed several molecular signaling pathways potentially linked to brain pathology and synaptic failure in AD, including AMP-activated protein kinase (AMPK), a master kinase that plays a central role in the maintenance of cellular energy homeostasis. Particularly, hyperactive AMPK via phosphorylation has been linked to AD-associated synaptic plasticity impairments, indicating suppression of AMPK activity might be beneficial for cognitive deficiency in AD. In this review, we will discuss how targeting dysregulation of AMPK signaling could be a feasible therapeutic approach for AD.

Distinct regulation of bioenergetics and translation by group I mGluR and NMDAR

Neuronal activity is responsible for the high energy consumption in the brain. However, the cellular mechanisms draining ATP upon the arrival of a stimulus are yet to be explored systematically at the post-synapse. Here, we provide evidence that a significant fraction of ATP is consumed upon glutamate stimulation to energize mGluR-induced protein synthesis. We find that both mGluR and NMDAR alter protein synthesis and ATP consumption with distinct kinetics at the synaptic-dendritic compartments. While mGluR activation leads to a rapid and sustained reduction in neuronal ATP levels, NMDAR activation has no immediate impact on the same. ATP consumption correlates inversely with the kinetics of protein synthesis for both receptors. We observe a persistent elevation in protein synthesis within 5 minutes of mGluR activation and a robust inhibition of the same within 2 minutes of NMDAR activation, assessed by the phosphorylation status of eEF2 and metabolic labeling. However, a delayed protein synthesis-dependent ATP expenditure ensues after 15 minutes of NMDAR stimulation. We identify a central role for AMPK in the correlation between protein synthesis and ATP consumption. AMPK is dephosphorylated and inhibited upon mGluR activation, while it is phosphorylated upon NMDAR activation. Perturbing AMPK activity disrupts receptor-specific modulations of eEF2 phosphorylation and protein synthesis. Our observations, therefore, demonstrate that the regulation of the AMPK-eEF2 signaling axis by glutamate receptors alters neuronal protein synthesis and bioenergetics.

Metformin and trimetazidine ameliorate diabetes-induced cognitive impediment in status epileptic rats

Patients with diabetes and epilepsy are more prone to cognitive impairment, dementia, and even Alzheimer's disease. Diabetes-induced inflammatory process is one of the main contributing factors; however, the impact on seizure is not clear. The current study is aimed to examine the role of metformin and trimetazidine in the reduction of neuronal damage caused by inflammatory mediators and apoptotic factors in diabetic epileptic rodent model. Diabetic epileptic rats received orally either metformin (100 mg/kg) or trimetazidine (10 mg/kg) for 3 weeks exhibited reduced cognitive function and ameliorated the disturbed brain neurotransmission. Besides, they improved both the inflammatory status and the histopathologic alterations. Administration of metformin or trimetazidine ameliorated the deterioration in cognitive function in Morris water maze (MWM) and reduced seizure score. Furthermore, brain neurotransmitters glutamate and γ-aminobutyric acid (GABA) were reverted back to their normal values. Both treatments reduced the rise in inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), apoptotic markers nuclear factor-κB (NF-κB) and caspase-3, and improved the pathological photomicrograph of the hippocampus of diabetic epileptic rats. Such effects were closely correlated to the observed increase in the adenosine triphosphate and adenosine diphosphate (ATP/ADP) ratio and reduction of death-associated protein (DAP) and mammalian target of rapamycin (mTOR). In conclusion, the current study shed light on the potential neuroprotective role of metformin and trimetazidine in the amelioration of cognitive function via hindering inflammatory processes in diabetic epileptic rats.

Energy efficient synaptic plasticity

Many aspects of the brain’s design can be understood as the result of evolutionary drive toward metabolic efficiency. In addition to the energetic costs of neural computation and transmission, experimental evidence indicates that synaptic plasticity is metabolically demanding as well. As synaptic plasticity is crucial for learning, we examine how these metabolic costs enter in learning. We find that when synaptic plasticity rules are naively implemented, training neural networks requires extremely large amounts of energy when storing many patterns. We propose that this is avoided by precisely balancing labile forms of synaptic plasticity with more stable forms. This algorithm, termed synaptic caching, boosts energy efficiency manifold and can be used with any plasticity rule, including back-propagation. Our results yield a novel interpretation of the multiple forms of neural synaptic plasticity observed experimentally, including synaptic tagging and capture phenomena. Furthermore, our results are relevant for energy efficient neuromorphic designs.

The brain expends a lot of energy. While the organ accounts for only about 2% of a person’s bodyweight, it is responsible for about 20% of our energy use at rest. Neurons use some of this energy to communicate with each other and to process information, but much of the energy is likely used to support learning. A study in fruit flies showed that insects that learned to associate two stimuli and then had their food supply cut off, died 20% earlier than untrained flies. This is thought to be because learning used up the insects’ energy reserves.

If learning a single association requires so much energy, how does the brain manage to store vast amounts of data? Li and van Rossum offer an explanation based on a computer model of neural networks. The advantage of using such a model is that it is possible to control and measure conditions more precisely than in the living brain.

Analysing the model confirmed that learning many new associations requires large amounts of energy. This is particularly true if the memories must be stored with a high degree of accuracy, and if the neural network contains many stored memories already. The reason that learning consumes so much energy is that forming long-term memories requires neurons to produce new proteins. Using the computer model, Li and van Rossum show that neural networks can overcome this limitation by storing memories initially in a transient form that does not require protein synthesis. Doing so reduces energy requirements by as much as 10-fold.

Studies in living brains have shown that transient memories of this type do in fact exist. The current results hence offer a hypothesis as to how the brain can learn in a more energy efficient way. Energy consumption is thought to have placed constraints on brain evolution. It is also often a bottleneck in computers. By revealing how the brain encodes memories energy efficiently, the current findings could thus also inspire new engineering solutions.

Antidiabetic Drug Metformin Ameliorates Depressive-Like Behavior in Mice with Chronic Restraint Stress via Activation of AMP-Activated Protein Kinase

Depression is one of the most prevalent neuropsychiatric disorders in modern society. However, traditional drugs, such as monoaminergic agents, have defect showing lag response requiring several weeks to months. Additionally, these drugs have limited efficacy and high resistance rates in patients with depression. Thus, there is an urgent need to develop novel drugs or approaches for the treatment of depression. Here, using biochemical, pharmacological, genetic and behavioral methods, we demonstrate that metformin imparts a fast-acting antidepressant-like effect in naïve mice as well as stressed mice subjected to chronic restraint stress model. Moreover, inhibition of AMP-activated protein kinase (AMPK) activity by compound C or knock down of hippocampal AMPKα occluded the antidepressant-like effect induced by metformin. Our results suggest that metformin may be a viable therapeutic drug for the treatment of stress-induced depression via activation of AMPK.

Spinal AMP kinase activity differentially regulates phrenic motor plasticity

Acute intermittent hypoxia (AIH) elicits phrenic motor plasticity via multiple distinct cellular mechanisms. With moderate AIH, phrenic motor facilitation (pMF) requires G_q protein-coupled serotonin type 2 receptor activation, ERK MAP kinase activity, and new synthesis of brain-derived neurotrophic factor. In contrast, severe AIH elicits pMF by an adenosine-dependent mechanism that requires exchange protein activated by cAMP, Akt, and mammalian target of rapamycin (mTOR) activity, followed by new tyrosine receptor kinase B protein synthesis; this same pathway is also initiated by G_s protein-coupled serotonin 7 receptors (5-HT₇). Because the metabolic sensor AMP-activated protein kinase (AMPK) inhibits mTOR-dependent protein synthesis, and mTOR signaling is necessary for 5-HT₇ but not 5-HT₂ receptor-induced pMF, we hypothesized that spinal AMPK activity differentially regulates pMF elicited by these distinct receptor subtypes. Serotonin type 2A receptor [5-HT_2A; (±)-2,5-dimethoxy-4-iodoamphetamine hydrochloride] or 5-HT₇ (AS-19) receptor agonists were administered intrathecally at C₄ (3 injections, 5-min intervals) while recording integrated phrenic nerve activity in anesthetized, vagotomized, paralyzed, and ventilated rats. Consistent with our hypothesis, spinal AMPK activation with 2-deoxyglucose or metformin blocked 5-HT₇, but not 5-HT_2A receptor-induced pMF; in both cases, pMF inhibition was reversed by spinal administration of the AMPK inhibitor compound C. Thus, AMPK differentially regulates cellular mechanisms of serotonin-induced phrenic motor plasticity.NEW & NOTEWORTHY Spinal AMP-activated protein kinase (AMPK) overactivity, induced by local 2-deoxyglucose or metformin administration, constrains serotonin 7 (5-HT₇) receptor-induced (but not serotonin type 2A receptor-induced) respiratory motor facilitation, indicating that metabolic challenges might regulate specific forms of respiratory motor plasticity. Pharmacological blockade of spinal AMPK activity restores 5-HT₇ receptor-induced respiratory motor facilitation in the presence of either 2-deoxyglucose or metformin, showing that AMPK is an important regulator of 5-HT₇ receptor-induced respiratory motor plasticity.

Metformin ameliorates stress-induced depression-like behaviors via enhancing the expression of BDNF by activating AMPK/CREB-mediated histone acetylation

BACKGROUND

Metformin, a first-line antiglycemic drug, has been reported to have anti-depressant effects in patients with type 2 diabetes; however, its exact role and underlying mechanism still need to be investigated.

METHOD

C57BL/6J mice were subjected to the Chronic social defeat stress (SDS) and drug administration (Control + Vehicle, SDS + Vehicle, SDS + MET (200 mg kg^-1), SDS + FLUOX (3 mg kg^-1), SDS + MET + FLUOX). And the depression phenotypes were evaluated by the sucrose preference test, social interaction, tail suspension test and forced swimming test. The potential mechanisms underlying the effects of metformin on depression was discussed by using Chromatin immunoprecipitation, Quantitative real-time PCR mRNA expression analysis and Western blot in vivo and in primary cultured hippocampal neurons.

RESULT

The metformin treatment counteracted the development of depression-like behaviors in mice suffering SDS when administered alone and enhanced the anti-depressant effect of fluoxetine when combined with fluoxetine. Further RNA sequencing analysis revealed that metformin treatment prevented the transcriptional changes in the medial prefrontal cortex (mPFC) of the animals and Golgi staining indicated favorable morphological changes in the neurite plasticity of CA1 pyramidal neurons, which approximated to those found in unstressed mice. At a molecular level, metformin significantly upregulated the expression of the brain-derived neurotrophic factor (BDNF) by increasing the histone acetylation along with the BDNF promoter, which was attributed to the activation of AMP-activated protein kinase (AMPK) and cAMP-response element binding protein (CREB).

CONCLUSION

Our findings suggest that metformin can produce antidepressant effects, which provides empirical insights into the clinical value of metformin in the prevention and therapy of depression.