Long-term potentiation is associated with an increased activity of Ca2+/calmodulin-dependent protein kinase II

Temporal-Specific Sex and Injury-Dependent Changes on Neurogranin-Associated Synaptic Signaling After Controlled Cortical Impact in Rats

Extensive effort has been made to study the role of synaptic deficits in cognitive impairment after traumatic brain injury (TBI). Neurogranin (Ng) is a calcium-sensitive calmodulin (CaM)-binding protein essential for Ca2+/CaM-dependent kinase II (CaMKII) autophosphorylation which subsequently modulates synaptic plasticity. Given the loss of Ng expression after injury, additional research is warranted to discern changes in hippocampal post-synaptic signaling after TBI. Under isoflurane anesthesia, adult, male and female Sprague-Dawley rats received a sham/control or controlled cortical impact (CCI) injury. Ipsilateral hippocampal synaptosomes were isolated at 24 h and 1, 2, and 4 weeks post-injury, and western blot was used to evaluate protein expression of Ng-associated signaling proteins. Non-parametric Mann-Whitney tests were used to determine significance of injury for each sex at each time point. There were significant changes in the hippocampal synaptic expression of Ng and associated synaptic proteins such as phosphorylated Ng, CaMKII, and CaM up to 4 weeks post-CCI, demonstrating TBI alters hippocampal post-synaptic signaling. This study furthers our understanding of mechanisms of cognitive dysfunction within the synapse sub-acutely after TBI.

Preventive effect of propolis on cognitive decline in Alzheimer's disease model mice

Brazilian green propolis (propolis) is a chemically complex resinous substance that is a potentially viable therapeutic agent for Alzheimer's disease. Herein, propolis induced a transient increase in intracellular Ca2+ concentration ([Ca2+]i) in Neuro-2A cells; moreover, propolis-induced [Ca2+]i elevations were suppressed prior to 24-h pretreatment with amyloid-β. To reveal the effect of [Ca2+]i elevation on impaired cognition, we performed memory-related behavioral tasks in APP-KI mice relative to WT mice at 4 and 12 months of age. Propolis, at 300-1000 mg/kg/d for 8 wk, significantly ameliorated cognitive deficits in APP-KI mice at 4 months, but not at 12 months of age. Consistent with behavioral observations, injured hippocampal long-term potentiation was markedly ameliorated in APP-KI mice at 4 months of age following repeated propolis administration. In addition, repeated administration of propolis significantly activated intracellular calcium signaling pathway in the CA1 region of APP-KI mice. These results suggest a preventive effect of propolis on cognitive decline through the activation of intracellular calcium signaling pathways in CA1 region of AD mice model.

CaMKII activity and metabolic imbalance-related neurological diseases: Focus on vascular dysfunction, synaptic plasticity, amyloid beta accumulation, and lipid metabolism

Metabolic syndrome (MetS) is characterized by insulin resistance, hyperglycemia, excessive fat accumulation and dyslipidemia, and is known to be accompanied by neuropathological symptoms such as memory loss, anxiety, and depression. As the number of MetS patients is rapidly increasing globally, studies on the mechanisms of metabolic imbalance-related neuropathology are emerging as an important issue. Ca2+/calmodulin-dependent kinase II (CaMKII) is the main Ca2+ sensor and contributes to diverse intracellular signaling in peripheral organs and the central nervous system (CNS). CaMKII exerts diverse functions in cells, related to mechanisms such as RNA splicing, reactive oxygen species (ROS) generation, cytoskeleton, and protein-protein interactions. In the CNS, CaMKII regulates vascular function, neuronal circuits, neurotransmission, synaptic plasticity, amyloid beta toxicity, lipid metabolism, and mitochondrial function. Here, we review recent evidence for the role of CaMKII in neuropathologic issues associated with metabolic disorders.

Abstinence and Fear Experienced during This Period Produce Distinct Cortical and Hippocampal Adaptations in Alcohol-Dependent Rats

Previous studies demonstrate that ethanol dependence induced by repeating cycles of chronic intermittent ethanol vapor exposure (CIE) followed by protracted abstinence produces significant gray matter damage via myelin dysfunction in the rodent medial prefrontal cortex (mPFC) and alterations in neuronal excitability in the mPFC and the dentate gyrus (DG) of the hippocampus. Specifically, abstinence-induced neuroadaptations have been associated with persistent elevated relapse to drinking. The current study evaluated the effects of forced abstinence for 1 day (d), 7 d, 21 d, and 42 d following seven weeks of CIE on synaptic plasticity proteins in the mPFC and DG. Immunoblotting revealed reduced expression of CaMKII in the mPFC and enhanced expression of GABAA and CaMKII in the DG at the 21 d time point, and the expression of the ratio of GluN2A/2B subunits did not change at any of the time points studied. Furthermore, cognitive performance via Pavlovian trace fear conditioning (TFC) was evaluated in 3 d abstinent rats, as this time point is associated with negative affect. In addition, the expression of the ratio of GluN2A/2B subunits and a 3D structural analysis of neurons in the mPFC and DG were evaluated in 3 d abstinent rats. Behavioral analysis revealed faster acquisition of fear responses and reduced retrieval of fear memories in CIE rats compared to controls. TFC produced hyperplasticity of pyramidal neurons in the mPFC under control conditions and this effect was not evident or blunted in abstinent rats. Neurons in the DG were unaltered. TFC enhanced the GluN2A/2B ratio in the mPFC and reduced the ratio in the DG and was not altered by abstinence. These findings indicate that forced abstinence from CIE produces distinct and divergent alterations in plasticity proteins in the mPFC and DG. Fear learning-induced changes in structural plasticity and proteins contributing to it were more profound in the mPFC during forced abstinence.

Repeated antibiotic drug treatment negatively affects memory function and glutamatergic nervous system of the hippocampus in mice

The gut microbiota is associated with memory; however, the relationship between dysbiosis-induced memory deficits and hippocampal glutamatergic neurons remains unclear. In our study, a mouse dysbiosis model showed impaired memory-related behavior in the passive avoidance test; decreased expression levels of glutaminase, excitatory amino acid transporter (EAAT)1, EAAT2, vesicular glutamate transporter 2, synaptophysin, brain-derived neurotrophic factor, doublecortin, neuronal nuclear protein, glial fibrillary acidic protein, and S100β; and decreased phosphorylation of N-methyl-D-aspartate receptor subunit 1, calmodulin-dependent protein kinase II, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit 1, and cAMP response element-binding protein in the hippocampus. This suggests that dysbiosis-induced memory dysfunction is associated with the hippocampal glutamatergic nervous system.

CaMKII: a central molecular organizer of synaptic plasticity, learning and memory

Calcium-calmodulin (CaM)-dependent protein kinase II (CaMKII) is the most abundant protein in excitatory synapses and is central to synaptic plasticity, learning and memory. It is activated by intracellular increases in calcium ion levels and triggers molecular processes necessary for synaptic plasticity. CaMKII phosphorylates numerous synaptic proteins, thereby regulating their structure and functions. This leads to molecular events crucial for synaptic plasticity, such as receptor trafficking, localization and activity; actin cytoskeletal dynamics; translation; and even transcription through synapse-nucleus shuttling. Several new tools affording increasingly greater spatiotemporal resolution have revealed the link between CaMKII activity and downstream signalling processes in dendritic spines during synaptic and behavioural plasticity. These technologies have provided insights into the function of CaMKII in learning and memory.

Propolis Promotes Memantine-Dependent Rescue of Cognitive Deficits in APP-KI Mice

Propolis is a complex resinous substance that is relevant as a therapeutic target for Alzheimer's disease (AD) and other neurodegenerative diseases. In this study, we confirmed that propolis (Brazilian green propolis) further enhances the rescue of cognitive deficits by the novel AD drug memantine in APP-KI mice. In memory-related behavior tasks, administration of a single dose of propolis at 1-100 mg/kg p.o. significantly enhanced the rescue of cognitive deficits by memantine at 1 mg/kg p.o. in APP-KI mice. In in vitro studies, propolis significantly increased intracellular Ca²⁺ concentration and calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation in Kir6.2-overexpressed N2A cells treated with memantine. Propolis also significantly increased adenosine 5'-triphosphate (ATP) contents and CaMKII autophosphorylation, which was impaired in Aβ-treated Kir6.2-overexpressed N2A cells. Similarly, repeated administration of propolis at 100 mg/kg p.o. for 8 weeks further enhanced the rescue of cognitive deficits by memantine in APP-KI mice. Consistent with the rescued cognitive deficits in APP-KI mice, repeated administration of propolis markedly ameliorated memantine-dependent rescue of injured long-term potentiation (LTP) in APP-KI mice, concomitant with increased CaMKII autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV) phosphorylation in the hippocampal CA1 region. Furthermore, repeated administration of both memantine and propolis significantly restored the decreased ATP contents in the CA1 region of APP-KI mice. Finally, we confirmed that repeated administration of memantine at 1 mg/kg p.o. and propolis at 100 mg/kg p.o. for 8 weeks failed to restore the cognitive deficits in Kir6.2-/- mice. Our study demonstrates that propolis increases ATP contents and promotes the amelioration of cognitive deficits rescued by memantine via Kir6.2 channel inhibition in the CA1 region.

Memantine improves cognitive deficits via KATP channel inhibition in olfactory bulbectomized mice

Patients with Alzheimer's disease (AD) demonstrate severely impaired olfactory systems, which occur in the early stages of the disease. Olfactory bulbectomy (OBX) in mice elicits cognitive deficits, and reduces cholinergic activity in the hippocampus. Here, we confirmed that the novel AD drug memantine rescues cognitive deficits via ATP-sensitive potassium (K_ATP) channel inhibition in OBX mice. Repeated memantine administration at 1-3 mg/kg p.o. for 14 days starting at 10 days after OBX surgery significantly rescued cognitive deficits in OBX mice, as assessed using Y-maze, novel object recognition, and passive avoidance tasks. Consistent with the rescued cognitive deficits in OBX mice, long-term potentiation (LTP) in the hippocampal cornu ammonis (CA) 1 region was markedly restored with memantine administration. As demonstrated by immunoblotting, the reductions of calcium/calmodulin-dependent protein kinase II (CaMKII) α (Thr-286) autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV; Thr-196) phosphorylation in the CA1 region of OBX mice were significantly restored with memantine. Conversely, pre-treatment with pinacidil, a K_ATP channel opener, failed to reinstate hippocampal LTP and CaMKII/CaMKIV activities in the CA1 region. Finally, improvement of cognitive deficits by memantine treatments was observed in OBX-operated Kir6.1 heterozygous (+/-) mice but not in OBX-operated Kir6.2 heterozygous (+/-) mice. Overall, our study demonstrates that memantine rescues OBX-induced cognitive deficits via Kir6.2 channel inhibition in the CA1 region.

Dynamic bi-directional phosphorylation events associated with the reciprocal regulation of synapses during homeostatic up- and down-scaling

Homeostatic synaptic scaling allows for bi-directional adjustment of the strength of synaptic connections in response to changes in their input. Protein phosphorylation modulates many neuronal processes, but it has not been studied on a global scale during synaptic scaling. Here, we use liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses to measure changes in the phosphoproteome in response to up- or down-scaling in cultured cortical neurons over minutes to 24 h. Of ~45,000 phosphorylation events, ~3,300 (associated with 1,285 phosphoproteins) are regulated by homeostatic scaling. Activity-sensitive phosphoproteins are predominantly located at synapses and involved in cytoskeletal reorganization. We identify many early phosphorylation events that could serve as sensors for the activity offset as well as late and/or persistent phosphoregulation that could represent effector mechanisms driving the homeostatic response. Much of the persistent phosphorylation is reciprocally regulated by up- or down-scaling, suggesting that mechanisms underlying these two poles of synaptic regulation make use of a common signaling axis.

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Global proteome and phosphoproteome dynamics following homeostatic synaptic scaling

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Approximately 3,300 activity-sensitive, synapse-associated phospho-events

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Persistent signaling of ~25% of initial phospho-events (min to 24 h)

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Persistent and reciprocal phosphoregulation links synaptic up- and down-scaling

Molecular mechanism of hippocampal long-term potentiation - Towards multiscale understanding of learning and memory

Long-term potentiation (LTP) of synaptic transmission is considered to be a cellular counterpart of learning and memory. Activation of postsynaptic NMDA type glutamate receptor (NMDA-R) induces trafficking of AMPA type glutamate receptors (AMPA-R) and other proteins to the synapse in sequential fashion. At the same time, the dendritic spine expands for long-term and modulation of actin underlies this (structural LTP or sLTP). How these changes persist despite constant diffusion and turnover of the component proteins have been the central focus of the current LTP research. Signaling triggered by Ca²⁺-influx via NMDA-R triggers kinase including Ca²⁺/calmodulin-dependent protein kinase II (CaMKII). CaMKII can sustain longer-term biochemical signaling by forming a reciprocally-activating kinase-effector complex with its substrate proteins including Tiam1, thereby regulating persistence of the downstream signaling. Furthermore, activated CaMKII can condense at the synapse through the mechanism of liquid-liquid phase separation (LLPS). This increases the binding capacity at the synapse, thereby contributing to the maintenance of enlarged protein complexes. It may also serve as the synapse tag, which captures newly synthesized proteins.

Calcium/Calmodulin-Dependent Protein Kinase II in Cerebrovascular Diseases

Cerebrovascular disease is the most common life-threatening and debilitating condition that often leads to stroke. The multifunctional calcium/calmodulin-dependent protein kinase II (CaMKII) is a key Ca2+ sensor and an important signaling protein in a variety of biological systems within the brain, heart, and vasculature. In the brain, past stroke-related studies have been mainly focused on the role of CaMKII in ischemic stroke in neurons and established CaMKII as a major mediator of neuronal cell death induced by glutamate excitotoxicity and oxidative stress following ischemic stroke. However, with growing understanding of the importance of neurovascular interactions in cerebrovascular diseases, there are clearly gaps in our understanding of how CaMKII functions in the complex neurovascular biological processes and its contributions to cerebrovascular diseases. Additionally, emerging evidence demonstrates novel regulatory mechanisms of CaMKII and potential roles of the less-studied CaMKII isoforms in the ischemic brain, which has sparked renewed interests in this dynamic kinase family. This review discusses past findings and emerging evidence on CaMKII in several major cerebrovascular dysfunctions including ischemic stroke, hemorrhagic stroke, and vascular dementia, focusing on the unique roles played by CaMKII in the underlying biological processes of neuronal cell death, neuroinflammation, and endothelial barrier dysfunction triggered by stroke. We also highlight exciting new findings, promising therapeutic agents, and future perspectives for CaMKII in cerebrovascular systems.

The role of CaMKII autophosphorylation for NMDA receptor-dependent synaptic potentiation

Potentiation of glutamatergic synaptic transmission is thought to underlie memory. The induction of this synaptic potentiation relies on activation of NMDA receptors which allows for calcium influx into the post-synapse. A key mechanistic question for the understanding of synaptic potentiation is what signaling is activated by the calcium influx. Here, I review evidences that at mature synapses the elevated calcium levels activate primarily calcium/calmodulin-dependent kinase II (CaMKII) and cause its autophophorylation. CaMKII autophosphorylation leads to calcium-independent activity of the kinase, so that kinase signaling can outlast NMDA receptor-dependent calcium influx. Prolonged CaMKII signaling induces downstream signaling for AMPA receptor trafficking into the post-synaptic density and causes structural enlargement of the synapse. Interestingly, however, CaMKII autophosphorylation does not have such an essential role in NMDA receptor-dependent synaptic potentiation in early postnatal development and in adult dentate gyrus, where neurogenesis occurs. Additionally, in old age memory-relevant NMDA receptor-dependent synaptic plasticity appears to be due to generation of multi-innervated dendritic spines, which does not require CaMKII autophosphorylation. In conclusion, CaMKII autophosphorylation has a conditional role in the induction of NMDA receptor-dependent synaptic potentiation.

The Calcium/Calmodulin-Dependent Kinases II and IV as Therapeutic Targets in Neurodegenerative and Neuropsychiatric Disorders

CaMKII and CaMKIV are calcium/calmodulin-dependent kinases playing a rudimentary role in many regulatory processes in the organism. These kinases attract increasing interest due to their involvement primarily in memory and plasticity and various cellular functions. Although CaMKII and CaMKIV are mostly recognized as the important cogs in a memory machine, little is known about their effect on mood and role in neuropsychiatric diseases etiology. Here, we aimed to review the structure and functions of CaMKII and CaMKIV, as well as how these kinases modulate the animals’ behavior to promote antidepressant-like, anxiolytic-like, and procognitive effects. The review will help in the understanding of the roles of the above kinases in the selected neurodegenerative and neuropsychiatric disorders, and this knowledge can be used in future drug design.

Scabronine G Methyl Ester Improves Memory-Related Behavior and Enhances Hippocampal Cell Proliferation and Long-Term Potentiation via the BDNF-CREB Pathway in Olfactory Bulbectomized Mice

A previous study reported that scabronine G methyl ester (SG-ME) potentially enhances the in vitro secretion of neurotrophic factors such as nerve growth factor via the protein kinase C (PKC)-ζ pathway. However, it remains unknown whether SG-ME can improve cognitive dysfunctions in olfactory bulbectomized (OBX) mice. To address this question, we evaluated SG-ME-treated and untreated OBX mice in a passive avoidance test. We also investigated potential effects of SG-ME on several parameters: cell proliferation and cAMP response element-binding protein (CREB) phosphorylation in the hippocampal dentate gyrus by immunohistochemistry, brain-derived neurotrophic factor (BDNF) levels in the hippocampus by Western blotting, p-CREB levels in the hippocampus by MapAnalyzer, and long-term potentiation (LTP) by electrophysiology. On the 14th day after surgery OBX mice showed altered passive avoidance and decreases in both cell proliferation and long-term potentiation in the hippocampus, while these changes were reversed by SG-ME (20 μg/mouse) 24 h after the treatment. The improvement in memory deficits was prevented when SG-ME was co-administeredwith either zeta inhibitory peptide (PKC-ζ inhibitor), anti-BDNF antibody, ANA-12 (TrkB antagonist), U0126 (MEK inhibitor), H-89 (PKA inhibitor), LY294002 (PI3K inhibitor) or KN-93 (CaMKII inhibitor). We found that SG-ME enhanced brain-derived neurotrophic factor and p-CREB levels in the hippocampus while p-CREB was localized in neurons, but not in astrocytes nor microglial cells. These findings revealed the potential of SG-ME in improving memory impairments by enhancing cell proliferation and LTP via activation of the BDNF/CREB signaling pathway in neurons.

The Emerging Role of LHb CaMKII in the Comorbidity of Depressive and Alcohol Use Disorders

Depressive disorders and alcohol use disorders are widespread among the general population and are significant public health and economic burdens. Alcohol use disorders often co-occur with other psychiatric conditions and this dual diagnosis is called comorbidity. Depressive disorders invariably contribute to the development and worsening of alcohol use disorders, and vice versa. The mechanisms underlying these disorders and their comorbidities remain unclear. Recently, interest in the lateral habenula, a small epithalamic brain structure, has increased because it becomes hyperactive in depression and alcohol use disorders, and can inhibit dopamine and serotonin neurons in the midbrain reward center, the hypofunction of which is believed to be a critical contributor to the etiology of depressive disorders and alcohol use disorders as well as their comorbidities. Additionally, calcium/calmodulin-dependent protein kinase II (CaMKII) in the lateral habenula has emerged as a critical player in the etiology of these comorbidities. This review analyzes the interplay of CaMKII signaling in the lateral habenula associated with depressive disorders and alcohol use disorders, in addition to the often-comorbid nature of these disorders. Although most of the CaMKII signaling pathway's core components have been discovered, much remains to be learned about the biochemical events that propagate and link between depression and alcohol abuse. As the field rapidly advances, it is expected that further understanding of the pathology involved will allow for targeted treatments.

CaM Kinase: Still Inspiring at 40

The Ca²⁺/calmodulin (CaM)-dependent protein kinase II (CaMKII) was touted as a memory molecule, even before its involvement in long-term potentiation (LTP) was shown. The enzyme has not disappointed, with subsequent demonstrations of remarkable structural and regulatory properties. Its neuronal functions now extend to long-term depression (LTD), and last year saw the first direct evidence for memory storage by CaMKII. Although CaMKII may have taken the spotlight, it is a member of a large family of diverse and interesting CaM kinases. Our aim is to place CaMKII in context of the other CaM kinases and then review certain aspects of this kinase that are of current interest.

Tubulin-Dependent Transport of Connexin-36 Potentiates the Size and Strength of Electrical Synapses

Connexin-36 (Cx36) electrical synapses strengthen transmission in a calcium/calmodulin (CaM)/calmodulin-dependent kinase II (CaMKII)-dependent manner similar to a mechanism whereby the N-methyl-D-aspartate (NMDA) receptor subunit NR2B facilitates chemical transmission. Since NR2B-microtubule interactions recruit receptors to the cell membrane during plasticity, we hypothesized an analogous modality for Cx36. We determined that Cx36 binding to tubulin at the carboxy-terminal domain was distinct from Cx43 and NR2B by binding a motif overlapping with the CaM and CaMKII binding motifs. Dual patch-clamp recordings demonstrated that pharmacological interference of the cytoskeleton and deleting the binding motif at the Cx36 carboxyl-terminal (CT) reversibly abolished Cx36 plasticity. Mechanistic details of trafficking to the gap-junction plaque (GJP) were probed pharmacologically and through mutational analysis, all of which affected GJP size and formation between cell pairs. Lys279, Ile280, and Lys281 positions were particularly critical. This study demonstrates that tubulin-dependent transport of Cx36 potentiates synaptic strength by delivering channels to GJPs, reinforcing the role of protein transport at chemical and electrical synapses to fine-tune communication between neurons.

Voluntary wheel running during adolescence distinctly alters running output in adulthood in male and female rats

Adult female rats show greater running output compared with age-matched male rats, and the midbrain dopaminergic system may account for behavioral differences in running output. However, it is unknown if the lower running output in adult males can be regulated by wheel running experience during adolescence, and whether wheel running experience during adolescence will diminish the sex differences in running output during adulthood. We therefore determined and compared the exercise output in adult male and female rats that either had initiated voluntary wheel running only during adulthood or during adolescence. Our results demonstrate that running output in adult males were significantly higher when running was initiated during adolescence, and this higher running output was not significantly different from females. Running output did not differ during adulthood in females when wheel running was initiated during adolescence or during adulthood. Higher running output in females was associated with reduced expression of tyrosine hydroxylase and hyperactivation of calcium/calmodulin-dependent protein kinase II (CaMKII) in the dorsal striatum. Notably, running during adolescence-induced higher exercise output in adult males was associated with hyperactivation of CaMKII in the dorsal striatum, indicating a mechanistic role for CaMKII in running output. Together, the present results indicate sexually dimorphic adaptive biochemical changes in the dorsal striatum in rats that had escalated running activity, and highlight the importance of including sex as a biological variable in exploring neuroplasticity changes that predict enhanced exercise output in a voluntary physical activity paradigm.

Interactome Analyses implicated CAMK2A in the genetic predisposition and pharmacological mechanism of Bipolar Disorder

Bipolar disorder (BPD) is a severe mental illness characterized by fluctuations in mood states, behaviors and energy levels. Growing evidence suggests that genes associated with specific illnesses tend to interact together and encode a tight protein-protein interaction (PPI) network, providing valuable information for understanding their pathogenesis. To gain insights into the genetic and physiological foundation of BPD, we conduct the physical PPI analysis of 184 BPD risk genes distilled from genome-wide association studies and exome sequencing studies. We have identified several hub genes (CAMK2A, HSP90AA1 and PLCG1) among those risk genes, and observed significant enrichment of the BPD risk genes in certain pathways such as calcium signaling, oxytocin signaling and circadian entrainment. Furthermore, while none of the 184 genetic risk genes are "well established" BPD drug targets, our PPI analysis showed that αCaMKII (encoded by CAMK2A) had direct physical PPIs with targets (HRH1, SCN5A and CACNA1E) of clinically used anti-manic BPD drugs, such as carbamazepine. We thus speculated that αCaMKII might be involved in the cellular pharmacological actions of those drugs. Using cultured rat primary cortical neurons, we found that carbamazepine treatment induced phosphorylation of αCaMKII in dose-dependent manners. Intriguingly, previous study showed that CAMK2A heterozygous knockout (CAMK2A^+/-) mice exhibited infradian oscillation of locomotor activities that can be rescued by carbamazepine. Our data, in combination with previous studies, provide convergent evidence for the involvement of CAMK2A in the risk of BPD.

Overexpression of activated CaMKII in the CA1 hippocampus impairs context discrimination, but not contextual conditioning

Calcium/Calmodulin-dependent protein kinase II (CaMKII) plays a key role in the molecular mechanism of memory formation. CaMKII is known to be activated specifically in the activated spines during memory formation. However, it is unclear whether the specific activation of CaMKII is necessary for encoding information. Here, we overexpressed active form of CaMKII (CaMKII*) in the hippocampal CA1 region to activate CaMKII nonspecifically. Moreover, we examined context-discrimination performance of mice. We found that the mice with overexpression of CaMKII* showed impaired context-discrimination ability, while the contextual fear conditioning remained intact. These results indicate that spatial specificity of CaMKII activation is necessary for context discrimination.

Antioxidant hydrolyzed peptides from Manchurian walnut (Juglans mandshurica Maxim.) attenuate scopolamine-induced memory impairment in mice

BACKGROUND

Walnut protein, which is obtained as a by-product of oil expression, has not been used efficiently. Although walnuts are beneficial for cognitive functioning, the potential of their protein composition in strengthening learning and memory functions remains unknown. In this study, the inhibition of memory impairment by the Manchurian walnut hydrolyzed peptide (MWHP) was evaluated.

RESULTS

Small-molecular-weight MWHP (<3 kDa) achieved the optimal antioxidative activity. Therefore, MWHP (<3 kDa) was subjected to the following mice trials to evaluate its attenuation effect on memory impairment. In the Morris water maze test, MWHP shortened the total path for searching the platform, reduced the escape latency, and increased the dwelling distance and time in the coverage zone. MWHP also prolonged the latency and diminished errors in the passive avoidance response tests. These behavioral tests demonstrated that MWHP could inhibit scopolamine-induced memory impairment. MWHP improved memory by reducing oxidative stress, inhibiting apoptosis, regulating neurotransmitter functions, maintaining hippocampal CA3 pyramidal neurons, and increasing calmodulin-dependent protein kinase II levels in brain tissues.

CONCLUSION

Experimental results proved that MWHP exhibits potential in improving memory and should be used to develop novel functional food. © 2018 Society of Chemical Industry.

Blockade of the KATP channel Kir6.2 by memantine represents a novel mechanism relevant to Alzheimer's disease therapy

Here, we report a novel target of the drug memantine, ATP-sensitive K⁺ (K_ATP) channels, potentially relevant to memory improvement. We confirmed that memantine antagonizes memory impairment in Alzheimer's model APP23 mice. Memantine increased CaMKII activity in the APP23 mouse hippocampus, and memantine-induced enhancement of hippocampal long-term potentiation (LTP) and CaMKII activity was totally abolished by treatment with pinacidil, a specific opener of K_ATP channels. Memantine also inhibited Kir6.1 and Kir6.2 K_ATP channels and elevated intracellular Ca²⁺ concentrations in neuro2A cells overexpressing Kir6.1 or Kir6.2. Kir6.2 was preferentially expressed at postsynaptic regions of hippocampal neurons, whereas Kir6.1 was predominant in dendrites and cell bodies of pyramidal neurons. Finally, we confirmed that Kir6.2 mutant mice exhibit severe memory deficits and impaired hippocampal LTP, impairments that cannot be rescued by memantine administration. Altogether, our studies show that memantine modulates Kir6.2 activity, and that the Kir6.2 channel is a novel target for therapeutics to improve memory impairment in Alzheimer disease patients.

Physiological and Pathological Roles of CaMKII-PP1 Signaling in the Brain

Ca²⁺/calmodulin (CaM)-dependent protein kinase II (CaMKII), a multifunctional serine (Ser)/threonine (Thr) protein kinase, regulates diverse activities related to Ca²⁺-mediated neuronal plasticity in the brain, including synaptic activity and gene expression. Among its regulators, protein phosphatase-1 (PP1), a Ser/Thr phosphatase, appears to be critical in controlling CaMKII-dependent neuronal signaling. In postsynaptic densities (PSDs), CaMKII is required for hippocampal long-term potentiation (LTP), a cellular process correlated with learning and memory. In response to Ca²⁺ elevation during hippocampal LTP induction, CaMKIIα, an isoform that translocates from the cytosol to PSDs, is activated through autophosphorylation at Thr286, generating autonomous kinase activity and a prolonged Ca²⁺/CaM-bound state. Moreover, PP1 inhibition enhances Thr286 autophosphorylation of CaMKIIα during LTP induction. By contrast, CaMKII nuclear import is regulated by Ser332 phosphorylation state. CaMKIIδ3, a nuclear isoform, is dephosphorylated at Ser332 by PP1, promoting its nuclear translocation, where it regulates transcription. In this review, we summarize physio-pathological roles of CaMKII/PP1 signaling in neurons. CaMKII and PP1 crosstalk and regulation of gene expression is important for neuronal plasticity as well as survival and/or differentiation.

Integrative Proteomics-Metabolomics Strategy for Pathological Mechanism of Vascular Depression Mouse Model

Vascular depression (VD), a subtype of depression, is caused by vascular diseases or cerebrovascular risk factors. Recently, the proportion of VD patients has increased significantly, which severely affects their quality of life. However, the current pathogenesis of VD has not yet been fully understood, and the basic research is not adequate. In this study, on the basis of the combination of LC-MS-based proteomics and metabolomics, we aimed to establish a protein metabolism regulatory network in a murine VD model to elucidate a more comprehensive impact of VD on organisms. We detected 44 metabolites and 304 proteins with different levels in the hippocampus samples from VD mice using a combination of metabolomic and proteomics analyses with an isobaric tags for relative and absolute quantification (iTRAQ) method. We constructed a protein-to-metabolic regulatory network by correlating and integrating the differential metabolites and proteins using ingenuity pathway analysis. Then we quantitatively validated the levels of the bimolecules shown in the bioinformatics analysis using LC-MS/MS and Western blotting. Validation results suggested changes in the regulation of neuroplasticity, transport of neurotransmitters, neuronal cell proliferation and apoptosis, and disorders of amino acids, lipids and energy metabolism. These proteins and metabolites involved in these dis-regulated pathways will provide a more targeted and credible direction to study the mechanism of VD. Therefore, this paper presents an approach and strategy that was applied in integrative proteomics and metabolomics for research and screening potential targets and biomarkers of VD, which could be more precise and credible in a field lacking adequate basic research.

A novel network analysis approach reveals DNA damage, oxidative stress and calcium/cAMP homeostasis-associated biomarkers in frontotemporal dementia

Frontotemporal Dementia (FTD) is the form of neurodegenerative dementia with the highest prevalence after Alzheimer’s disease, equally distributed in men and women. It includes several variants, generally characterized by behavioural instability and language impairments. Although few mendelian genes (MAPT, GRN, and C9orf72) have been associated to the FTD phenotype, in most cases there is only evidence of multiple risk loci with relatively small effect size. To date, there are no comprehensive studies describing FTD at molecular level, highlighting possible genetic interactions and signalling pathways at the origin FTD-associated neurodegeneration. In this study, we designed a broad FTD genetic interaction map of the Italian population, through a novel network-based approach modelled on the concepts of disease-relevance and interaction perturbation, combining Steiner tree search and Structural Equation Model (SEM) analysis. Our results show a strong connection between Calcium/cAMP metabolism, oxidative stress-induced Serine/Threonine kinases activation, and postsynaptic membrane potentiation, suggesting a possible combination of neuronal damage and loss of neuroprotection, leading to cell death. In our model, Calcium/cAMP homeostasis and energetic metabolism impairments are primary causes of loss of neuroprotection and neural cell damage, respectively. Secondly, the altered postsynaptic membrane potentiation, due to the activation of stress-induced Serine/Threonine kinases, leads to neurodegeneration. Our study investigates the molecular underpinnings of these processes, evidencing key genes and gene interactions that may account for a significant fraction of unexplained FTD aetiology. We emphasized the key molecular actors in these processes, proposing them as novel FTD biomarkers that could be crucial for further epidemiological and molecular studies.

Memory Erasure Experiments Indicate a Critical Role of CaMKII in Memory Storage

The abundant synaptic protein CaMKII is necessary for long-term potentiation (LTP) and memory. However, whether CaMKII is required only during initial processes or whether it also mediates memory storage remains unclear. The most direct test of a storage role is the erasure test. In this test, a putative memory molecule is inhibited after learning. The key prediction is that this should produce persistent memory erasure even after the inhibitory agent is removed. We conducted this test using transient viral (HSV) expression of dominant-negative CaMKII-alpha (K42M) in the hippocampus. This produced persistent erasure of conditioned place avoidance. As an additional test, we found that expression of activated CaMKII (T286D/T305A/T306A) impaired place avoidance, a result not expected if a process other than CaMKII stores memory. Our behavioral results, taken together with prior experiments on LTP, strongly support a critical role of CaMKII in LTP maintenance and memory storage.

Kinetics of Endogenous CaMKII Required for Synaptic Plasticity Revealed by Optogenetic Kinase Inhibitor

Elucidating temporal windows of signaling activity required for synaptic and behavioral plasticity is crucial for understanding molecular mechanisms underlying these phenomena. Here, we developed photoactivatable autocamtide inhibitory peptide 2 (paAIP2), a genetically encoded, light-inducible inhibitor of CaMKII activity. The photoactivation of paAIP2 in neurons for 1-2 min during the induction of LTP and structural LTP (sLTP) of dendritic spines inhibited these forms of plasticity in hippocampal slices of rodents. However, photoactivation ∼1 min after the induction did not affect them, suggesting that the initial 1 min of CaMKII activation is sufficient for inducing LTP and sLTP. Furthermore, the photoactivation of paAIP2 expressed in amygdalar neurons of mice during an inhibitory avoidance task revealed that CaMKII activity during, but not after, training is required for the memory formation. Thus, we demonstrated that paAIP2 is useful to elucidate the temporal window of CaMKII activation required for synaptic plasticity and learning.

Differential involvement of Ca2+/calmodulin-dependent protein kinases and mitogen-activated protein kinases in the dopamine D1/D5 receptor-mediated potentiation in hippocampal CA1 pyramidal neurons

Dopaminergic neurotransmission modulates and influences hippocampal CA1 synaptic plasticity, learning and long-term memory mechanisms. Investigating the mechanisms involved in the slow-onset potentiation induced by the dopamine D1/D5 receptor agonists in hippocampal CA1 region, we have reported recently that it could play a role in regulating synaptic cooperation and competition. We have also shown that a sustained activation of MEK/MAP kinase pathway was involved in the maintenance of this long-lasting potentiation (Shivarama Shetty, Gopinadhan, & Sajikumar, 2016). However, the molecular aspects of the induction of dopaminergic slow-onset potentiation are not known. Here, we investigated the involvement of MEK/MAPK pathway and Ca²⁺-calmodulin-dependent protein kinases (CaMKII and CaMKIV) in the induction and maintenance phases of the D1/D5 receptor-mediated slow-onset potentiation. We report differential involvement of these kinases in a dose-dependent manner wherein at weaker levels of dopaminergic activation, both CaMKII and MEK1/2 activation is necessary for the establishment of potentiation and with sufficiently stronger dopaminergic activation, the role of CaMKII becomes dispensable whereas MEK activation remains crucial for the long-lasting potentiation. The results are interesting in view of the involvement of the hippocampal dopaminergic system in a variety of cognitive abilities including memory formation and also in neurological diseases such as Alzheimer's disease and Parkinson's disease.

Functional Relevance of Different Basal Ganglia Pathways Investigated in a Spiking Model with Reward Dependent Plasticity

The brain enables animals to behaviorally adapt in order to survive in a complex and dynamic environment, but how reward-oriented behaviors are achieved and computed by its underlying neural circuitry is an open question. To address this concern, we have developed a spiking model of the basal ganglia (BG) that learns to dis-inhibit the action leading to a reward despite ongoing changes in the reward schedule. The architecture of the network features the two pathways commonly described in BG, the direct (denoted D1) and the indirect (denoted D2) pathway, as well as a loop involving striatum and the dopaminergic system. The activity of these dopaminergic neurons conveys the reward prediction error (RPE), which determines the magnitude of synaptic plasticity within the different pathways. All plastic connections implement a versatile four-factor learning rule derived from Bayesian inference that depends upon pre- and post-synaptic activity, receptor type, and dopamine level. Synaptic weight updates occur in the D1 or D2 pathways depending on the sign of the RPE, and an efference copy informs upstream nuclei about the action selected. We demonstrate successful performance of the system in a multiple-choice learning task with a transiently changing reward schedule. We simulate lesioning of the various pathways and show that a condition without the D2 pathway fares worse than one without D1. Additionally, we simulate the degeneration observed in Parkinson's disease (PD) by decreasing the number of dopaminergic neurons during learning. The results suggest that the D1 pathway impairment in PD might have been overlooked. Furthermore, an analysis of the alterations in the synaptic weights shows that using the absolute reward value instead of the RPE leads to a larger change in D1.

REVIEW ■ : LTP and LTD: Dynamic and Interactive Processes of Synaptic Plasticity

Long-lasting, activity-dependent changes in the efficacy of synaptic transmission are considered to be of fundamental importance for the storage of information and for the development of neural circuitry. The leading experimental model for such a change has been long-term potentiation (LTP), a long-lasting increase in synaptic strength. Intensive experimental analysis of LTP in the hippocampus has resulted in a detailed description of the initial steps responsible for its generation. Recently, a form of long-term depression (LTD) in the hippocampus has been described and examined. It shares several mechanistic features with LTP and appears to be able to reverse LTP. The intracellular second messenger systems that are required to generate and maintain LTP and LTD have been difficult to identify definitively. Leading candidates include diffusible intercellular messengers as well as protein kinases and protein phosphatases, the activities of which may converge at the level of specific phosphoproteins. In addition to delineating the cellular mechanisms under lying LTP and LTD, investigators also are beginning to clarify the roles they play in real learning and memory. The Neuroscientist 1:35-42, 1995

Facilitation of AMPA receptor-mediated steady-state current by extrasynaptic NMDA receptors in supraoptic magnocellular neurosecretory cells

In addition to classical synaptic transmission, information is transmitted between cells via the activation of extrasynaptic receptors that generate persistent tonic current in the brain. While growing evidence supports the presence of tonic NMDA current (I_NMDA) generated by extrasynaptic NMDA receptors (eNMDARs), the functional significance of tonic I_NMDA in various brain regions remains poorly understood. Here, we demonstrate that activation of eNMDARs that generate I_NMDA facilitates the α-amino-3-hydroxy-5-methylisoxazole-4-proprionate receptor (AMPAR)-mediated steady-state current in supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs). In low-Mg²⁺ artificial cerebrospinal fluid (aCSF), glutamate induced an inward shift in I_holding (I_GLU) at a holding potential (V_holding) of –70 mV which was partly blocked by an AMPAR antagonist, NBQX. NBQX-sensitive I_GLU was observed even in normal aCSF at V_holding of –40 mV or –20 mV. I_GLU was completely abolished by pretreatment with an NMDAR blocker, AP5, under all tested conditions. AMPA induced a reproducible inward shift in I_holding (I_AMPA) in SON MNCs. Pretreatment with AP5 attenuated I_AMPA amplitudes to ~60% of the control levels in low-Mg²⁺ aCSF, but not in normal aCSF at V_holding of –70 mV. I_AMPA attenuation by AP5 was also prominent in normal aCSF at depolarized holding potentials. Memantine, an eNMDAR blocker, mimicked the AP5-induced I_AMPA attenuation in SON MNCs. Finally, chronic dehydration did not affect I_AMPA attenuation by AP5 in the neurons. These results suggest that tonic I_NMDA, mediated by eNMDAR, facilitates AMPAR function, changing the postsynaptic response to its agonists in normal and osmotically challenged SON MNCs.

Herbal formula GAPT prevents beta amyloid deposition induced Ca(2+)/Calmodulin-dependent protein kinase II and Ca(2+)/Calmodulin-dependent protein phosphatase 2B imbalance in APPV717I mice

Background

Synaptic dysfunction is one of the pathological characteristics of Alzheimer's disease (AD), which is directly related to the progressive decline of cognitive function. CaMKII and CaN have been found to play important roles in memory processes and synaptic transmission. So present study aimed to elucidate relationships between CaMKII, CaN and cognitive decline in APPV717I mice, and to reveal whether the cognitive improving effects of GAPT is conducted through rebalance CaMKII and CaN.

Methods

Three-month-old-male APPV717I mice were randomly divided into ten groups (n = 12 per group) and received intragastrically administrated vehicle, donepezil or different doses of herbal formula GAPT for 8 or 4 months. Three-month-old male C57BL/6 J mice was set as vehicle control.

Results

Immunohistochemistry analysis showed that there were CaMKII expression decrease in the CA1 region of APPV717I transgenic mice, while the CaMKII expression of donepezil or GAPT treated transgenic mice were all increased. And there were CaN expression increase in the brain cortex of APPV717I transgenic mice, while there were decrease of CaN expression in donepezil or GAPT treated transgenic group. Western blot analysis showed the similar expression pattern without significant difference.

Conclusion

GAPT extract have showed effectiveness in activating the expression of CaMKII and inhibiting the expression of CaN either before or after the formation of amyloid plaques in the brain of APPV717I transgenic mice, which may in certain way alleviated neuron synaptic dysfunction in AD.

Hippocampal Transcriptome Profile of Persistent Memory Rescue in a Mouse Model of THRA1 Mutation-Mediated Resistance to Thyroid Hormone

Hypothyroidism due to THRA1 (gene coding for thyroid hormone receptor α1) mutation-mediated Resistance to Thyroid Hormone (RTH) has been recently reported in human and is associated with memory deficits similar to those found in a mouse model for Thra1 mutation mediated RTH (Thra1^+/m mice). Here, we show that a short-term treatment of Thra1^+/m mice with GABA_A receptor antagonist pentylenetetrazol (PTZ) completely and durably rescues their memory performance. In the CA1 region of the hippocampus, improvement of memory is associated with increased in long-term potentiation (LTP) and an augmentation of density of dendritic spines (DDS) onto the apical dendrites of pyramidal cells reflecting an increase in the local excitatory drive. Unbiased gene profiling analysis of hippocampi of treated Thra1^+/+ and Thra1^+/m mice were performed two weeks and three months post treatment and identified co-expression modules that include differentially expressed genes related with and predicting higher memory, LTP and DDS in the hippocampi of PTZ-treated animals. We observed that PTZ treatment changed similar sets of genes in both Thra1^+/+ and Thra1^+/m mice, which are known to be involved in memory consolidation and neurotransmission dynamics and could participate in the persistent effects of PTZ on memory recovery.

Fast Decay of CaMKII FRET Sensor Signal in Spines after LTP Induction Is Not Due to Its Dephosphorylation

Because CaMKII is the critical Ca(2+) sensor that triggers long-term potentiation (LTP), understanding its activation and deactivation is important. A major advance has been the development of a FRET indicator of the conformational state of CaMKII called Camui. Experiments using Camui have demonstrated that the open (active) conformation increases during LTP induction and then decays in tens of seconds, with the major fast component decaying with a time-constant of ~ 6 sec (tau1). Because this decay is faster if autophosphorylation of T286 is prevented (the autophosphorylation prolongs activity by making the enzyme active even after Ca(2+) falls), it seemed likely that the fast decay is due to the T286 dephosphorylation. To test this interpretation, we studied the effect of phosphatase inhibitors on the single-spine Camui signal evoked by two-photon glutamate uncaging. We applied inhibitors of PP1 and PP2A, two phosphatases that are present at synapses and that have been shown to dephosphorylate CaMKII in vitro. The inhibitors increased the basal Camui activation state, indicating their effectiveness in cells. However, in no case did we find that tau1 was prolonged, contrary to what would be expected if the decay was phosphatase-dependent. This could either mean that decay was due to some unknown phosphatase or that the decay was not due to dephosphorylation. To distinguish between these possibilities, we expressed pseudo-phosphorylated Camui (T286D) (plus additional mutations [T/A] that prevented inhibitory 305/306 phosphorylation). This form had an elevated basal activation state, but was further activated during glutamate uncaging; importantly the activation state decayed with tau1 nearly the same as that of WT Camui. Therefore, the data strongly indicate that tau1 is not due to T286 dephosphorylation. We conclude that, although Camui is an excellent tool for observing CaMKII signaling, further experimentation is needed to determine how CaMKII is turned off by its dephosphorylation.

Development of a molecularly evolved, highly sensitive CaMKII FRET sensor with improved expression pattern

Genetically encoded fluorescence resonance energy transfer (FRET) biosensors have been successfully used to visualize protein activity in living cells. The sensitivity and accuracy of FRET measurements directly depend on biosensor folding efficiency, expression pattern, sensitivity, and dynamic range. Here, to improve the folding efficiency of the Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIα) FRET biosensor, we amplified the association domain of the CaMKIIα gene using error-prone polymerase chain reaction (PCR) and fused it to the N-terminus of mCherry in a bacterial expression vector. We also created an Escherichia coli expression library based on a previously reported fluorescent protein folding reporter method, and found a bright red fluorescent colony that contained the association domain with four mutations (F394L, I419V, A430T, and I434T). In vitro assays using the purified mutant protein confirmed improved folding kinetics of the downstream fluorescent protein, but not of the association domain itself. Furthermore, we introduced these mutations into the previously reported CaMKIIα FRET sensor and monitored its Ca2+/calmodulin-dependent activation in HeLa cells using 2-photon fluorescence lifetime imaging microscopy (2pFLIM), and found that the expression pattern and signal reproducibility of the mutant sensor were greatly improved without affecting the autophosphorylation function and incorporation into oligomeric CaMKIIα. We believe that our improved CaMKIIα FRET sensor would be useful in various types of cells and tissues, providing data with high accuracy and reproducibility. In addition, the method described here may also be applicable for improving the performance of all currently available FRET sensors.

Long-term potentiation can be induced in the CA1 region of hippocampus in the absence of αCaMKII T286-autophosphorylation

α-calcium/calmodulin-dependent protein kinase (αCaMKII) T286-autophosphorylation provides a short-term molecular memory that was thought to be required for LTP and for learning and memory. However, it has been shown that learning can occur in αCaMKII-T286A mutant mice after a massed training protocol. This raises the question of whether there might be a form of LTP in these mice that can occur without T286 autophosphorylation. In this study, we confirmed that in CA1 pyramidal cells, LTP induced in acute hippocampal slices, after a recovery period in an interface chamber, is strictly dependent on postsynaptic αCaMKII autophosphorylation. However, we demonstrated that αCaMKII-autophosphorylation-independent plasticity can occur in the hippocampus but at the expense of synaptic specificity. This nonspecific LTP was observed in mutant and wild-type mice after a recovery period in a submersion chamber and was independent of NMDA receptors. Moreover, when slices prepared from mutant mice were preincubated during 2 h with rapamycin, high-frequency trains induced a synapse-specific LTP which was added to the nonspecific LTP. This specific LTP was related to an increase in the duration and the amplitude of NMDA receptor-mediated response induced by rapamycin.

Opposite regulation of inhibitory synaptic plasticity by α and β subunits of Ca(2+)/calmodulin-dependent protein kinase II

Induction of several forms of synaptic plasticity, a cellular basis for learning and memory, depends on the activation of Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII). CaMKII acts as a holoenzyme consisting of α and β subunits (α- and βCaMKII). However, it remains elusive how the subunit composition of a CaMKII holoenzyme affects its activation and hence synaptic plasticity. We addressed this issue by focusing on long-term potentiation (LTP) at inhibitory synapses on cerebellar Purkinje neurons (PNs) (called rebound potentiation, RP). The contribution of each subunit to RP was examined by selective knock-down or overexpression of that subunit. Electrophysiological recording from a rat cultured PN demonstrated that βCaMKII is essential for RP induction, whereas αCaMKII suppresses it. Thus, RP was negatively regulated due to the greater relative abundance of αCaMKII compared to βCaMKII, suggesting a critical role of CaMKII subunit composition in RP. The higher affinity of βCaMKII to Ca(2+)/CaM compared with αCaMKII was responsible for the predominant role in RP induction. Live-cell imaging of CaMKII activity based on the Förster resonance energy transfer (FRET) technique revealed that βCaMKII enrichment enhances the total CaMKII activation upon a transient conditioning depolarization. Taken together, these findings clarified that α- and βCaMKII oppositely regulate CaMKII activation, controlling the induction of inhibitory synaptic plasticity in a PN, which might contribute to the adaptive information processing of the cerebellar cortex.

Signaling to the microtubule cytoskeleton: an unconventional role for CaMKII

Synaptic plasticity is a hallmark of the nervous system and is thought to be integral to higher brain functions such as learning and memory. Calcium, acting as a second messenger, and the calcium/calmodulin dependent kinase CaMKII are key regulators of neuronal plasticity. Given the importance of the actin and microtubule (MT) cytoskeleton in dendritic spine morphology, composition and plasticity, it is not surprising that many regulators of these cytoskeletal elements are downstream of the CaMKII pathway. In this review, we discuss the emerging role of calcium and CaMKII in the regulation of MTs and cargo unloading during synaptic plasticity.

Synaptic and nonsynaptic plasticity approximating probabilistic inference

Learning and memory operations in neural circuits are believed to involve molecular cascades of synaptic and nonsynaptic changes that lead to a diverse repertoire of dynamical phenomena at higher levels of processing. Hebbian and homeostatic plasticity, neuromodulation, and intrinsic excitability all conspire to form and maintain memories. But it is still unclear how these seemingly redundant mechanisms could jointly orchestrate learning in a more unified system. To this end, a Hebbian learning rule for spiking neurons inspired by Bayesian statistics is proposed. In this model, synaptic weights and intrinsic currents are adapted on-line upon arrival of single spikes, which initiate a cascade of temporally interacting memory traces that locally estimate probabilities associated with relative neuronal activation levels. Trace dynamics enable synaptic learning to readily demonstrate a spike-timing dependence, stably return to a set-point over long time scales, and remain competitive despite this stability. Beyond unsupervised learning, linking the traces with an external plasticity-modulating signal enables spike-based reinforcement learning. At the postsynaptic neuron, the traces are represented by an activity-dependent ion channel that is shown to regulate the input received by a postsynaptic cell and generate intrinsic graded persistent firing levels. We show how spike-based Hebbian-Bayesian learning can be performed in a simulated inference task using integrate-and-fire (IAF) neurons that are Poisson-firing and background-driven, similar to the preferred regime of cortical neurons. Our results support the view that neurons can represent information in the form of probability distributions, and that probabilistic inference could be a functional by-product of coupled synaptic and nonsynaptic mechanisms operating over several timescales. The model provides a biophysical realization of Bayesian computation by reconciling several observed neural phenomena whose functional effects are only partially understood in concert.

The delicate bistability of CaMKII

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a synaptic, autophosphorylating kinase that is essential for learning and memory. Previous models have suggested that CaMKII functions as a bistable switch that could be the molecular correlate of long-term memory, but experiments have failed to validate these predictions. These models involved significant approximations to overcome the combinatorial complexity inherent in a multisubunit, multistate system. Here, we develop a stochastic particle-based model of CaMKII activation and dynamics that overcomes combinatorial complexity without significant approximations. We report four major findings. First, the CaMKII model system is never bistable at resting calcium concentrations, which suggests that CaMKII activity does not function as the biochemical switch underlying long-term memory. Second, the steady-state activation curves are either laserlike or steplike. Both are characterized by a well-defined threshold for activation, which suggests that thresholding is a robust feature of this system. Third, transiently activated CaMKII can maintain its activity over the time course of many experiments, and such slow deactivation may account for the few reports of bistability in the literature. And fourth, under in vivo conditions, increases in phosphatase activity can increase CaMKII activity. This is a surprising and counterintuitive effect, as dephosphorylation is generally associated with CaMKII deactivation.

Oxidative stress and neurodegenerative disorders

Living cells continually generate reactive oxygen species (ROS) through the respiratory chain during energetic metabolism. ROS at low or moderate concentration can play important physiological roles. However, an excessive amount of ROS under oxidative stress would be extremely deleterious. The central nervous system (CNS) is particularly vulnerable to oxidative stress due to its high oxygen consumption, weakly antioxidative systems and the terminal-differentiation characteristic of neurons. Thus, oxidative stress elicits various neurodegenerative diseases. In addition, chemotherapy could result in severe side effects on the CNS and peripheral nervous system (PNS) of cancer patients, and a growing body of evidence demonstrates the involvement of ROS in drug-induced neurotoxicities as well. Therefore, development of antioxidants as neuroprotective drugs is a potentially beneficial strategy for clinical therapy. In this review, we summarize the source, balance maintenance and physiologic functions of ROS, oxidative stress and its toxic mechanisms underlying a number of neurodegenerative diseases, and the possible involvement of ROS in chemotherapy-induced toxicity to the CNS and PNS. We ultimately assess the value for antioxidants as neuroprotective drugs and provide our comments on the unmet needs.