Postsynaptic protein phosphorylation and LTP

Serotonergic neuromodulation of synaptic plasticity

Synaptic plasticity constitutes a fundamental process in the reorganization of neural networks that underlie memory, cognition, emotional responses, and behavioral planning. At the core of this phenomenon lie Hebbian mechanisms, wherein frequent synaptic stimulation induces long-term potentiation (LTP), while less activation leads to long-term depression (LTD). The synaptic reorganization of neuronal networks is regulated by serotonin (5-HT), a neuromodulator capable of modify synaptic plasticity to appropriately respond to mental and behavioral states, such as alertness, attention, concentration, motivation, and mood. Lately, understanding the serotonergic Neuromodulation of synaptic plasticity has become imperative for unraveling its impact on cognitive, emotional, and behavioral functions. Through a comparative analysis across three main forebrain structures-the hippocampus, amygdala, and prefrontal cortex, this review discusses the actions of 5-HT on synaptic plasticity, offering insights into its role as a neuromodulator involved in emotional and cognitive functions. By distinguishing between plastic and metaplastic effects, we provide a comprehensive overview about the mechanisms of 5-HT neuromodulation of synaptic plasticity and associated functions across different brain regions.

Interplay of hippocampal long-term potentiation and long-term depression in enabling memory representations

Hippocampal long-term potentiation (LTP) and long-term depression (LTD) are Hebbian forms of synaptic plasticity that are widely believed to comprise the physiological correlates of associative learning. They comprise a persistent, input-specific increase or decrease, respectively, in synaptic efficacy that, in rodents, can be followed for days and weeks in vivo. Persistent (>24 h) LTP and LTD exhibit distinct frequency-dependencies and molecular profiles in the hippocampal subfields. Moreover, causal and genetic studies in behaving rodents indicate that both LTP and LTD fulfil specific and complementary roles in the acquisition and retention of spatial memory. LTP is likely to be responsible for the generation of a record of spatial experience, which may serve as an associative schema that can be re-used to expedite or facilitate subsequent learning. In contrast, LTD may enable modification and dynamic updating of this representation, such that detailed spatial content information is included and the schema is rendered unique and distinguishable from other similar representations. Together, LTP and LTD engage in a dynamic interplay that supports the generation of complex associative memories that are resistant to generalization. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Changes in hippocampal volume, synaptic plasticity and amylin sensitivity in an animal model of type 2 diabetes are associated with increased vulnerability to amyloid-beta in advancing age

Type-2 diabetes (T2D) is a metabolic disorder that is considered a risk factor for Alzheimer's disease (AD). Cognitive impairment can arise due to hypoglycemia associated with T2D, and hyperamylinemia associated with insulin resistance can enhance AD pathology. We explored whether changes occur in the hippocampus in aging (6-12 months old) female V-Lep○b-/- transgenic (tg) mice, comprising an animal model of T2D. We also investigated whether an increase in vulnerability to Aβ (1-42), a known pathological hallmark of AD, is evident. Using magnetic resonance imaging we detected significant decreases in hippocampal brain volume in female tg-mice compared to wild-type (wt) littermates. Long-term potentiation (LTP) was impaired in tg compared to wt mice. Treatment of the hippocampus with Aβ (1-42) elicited a stronger debilitation of LTP in tg compared to wt mice. Treatment with an amylin antagonist (AC187) significantly enhanced LTP in wt and tg mice, and rescued LTP in Aβ (1-42)-treated tg mice. Taken together our data indicate that a T2D-like state results in an increased vulnerability of the hippocampus to the debilitating effects of Aβ (1-42) and that effects are mediated in part by changes in amylin receptor signaling.

Hepatic kynurenic acid mediates phosphorylation of Nogo-A in the medial prefrontal cortex to regulate chronic stress-induced anxiety-like behaviors in mice

Exercise training effectively relieves anxiety disorders via modulating specific brain networks. The role of post-translational modification of proteins in this process, however, has been underappreciated. Here we performed a mouse study in which chronic restraint stress-induced anxiety-like behaviors can be attenuated by 14-day persistent treadmill exercise, in association with dramatic changes of protein phosphorylation patterns in the medial prefrontal cortex (mPFC). In particular, exercise was proposed to modulate the phosphorylation of Nogo-A protein, which drives the ras homolog family member A (RhoA)/ Rho-associated coiled-coil-containing protein kinases 1(ROCK1) signaling cascade. Further mechanistic studies found that liver-derived kynurenic acid (KYNA) can affect the kynurenine metabolism within the mPFC, to modulate this RhoA/ROCK1 pathway for conferring stress resilience. In sum, we proposed that circulating KYNA might mediate stress-induced anxiety-like behaviors via protein phosphorylation modification within the mPFC, and these findings shed more insights for the liver-brain communications in responding to both stress and physical exercise.

Post-ischemic ubiquitination at the postsynaptic density reversibly influences the activity of ischemia-relevant kinases

Ubiquitin modifications alter protein function and stability, thereby regulating cell homeostasis and viability, particularly under stress. Ischemic stroke induces protein ubiquitination at the ischemic periphery, wherein cells remain viable, however the identity of ubiquitinated proteins is unknown. Here, we employed a proteomics approach to identify these proteins in mice undergoing ischemic stroke. The data are available in a searchable web interface ( https://hochrainerlab.shinyapps.io/StrokeUbiOmics/ ). We detected increased ubiquitination of 198 proteins, many of which localize to the postsynaptic density (PSD) of glutamatergic neurons. Among these were proteins essential for maintaining PSD architecture, such as PSD95, as well as NMDA and AMPA receptor subunits. The largest enzymatic group at the PSD with elevated post-ischemic ubiquitination were kinases, such as CaMKII, PKC, Cdk5, and Pyk2, whose aberrant activities are well-known to contribute to post-ischemic neuronal death. Concurrent phospho-proteomics revealed altered PSD-associated phosphorylation patterns, indicative of modified kinase activities following stroke. PSD-located CaMKII, PKC, and Cdk5 activities were decreased while Pyk2 activity was increased after stroke. Removal of ubiquitin restored kinase activities to pre-stroke levels, identifying ubiquitination as the responsible molecular mechanism for post-ischemic kinase regulation. These findings unveil a previously unrecognized role of ubiquitination in the regulation of essential kinases involved in ischemic injury.

Notch receptor-ligand binding facilitates extracellular vesicle-mediated neuron-to-neuron communication

Extracellular vesicles (EVs) facilitate intercellular communication by transferring cargo between cells in a variety of tissues. However, how EVs achieve cell-type-specific intercellular communication is still largely unknown. We found that Notch1 and Notch2 proteins are expressed on the surface of neuronal EVs that have been generated in response to neuronal excitatory synaptic activity. Notch ligands bind these EVs on the neuronal plasma membrane, trigger their internalization, activate the Notch signaling pathway, and drive the expression of Notch target genes. The generation of these neuronal EVs requires the endosomal sorting complex required for transport-associated protein Alix. Adult Alix conditional knockout mice have reduced hippocampal Notch signaling activation and glutamatergic synaptic protein expression. Thus, EVs facilitate neuron-to-neuron communication via the Notch receptor-ligand system in the brain.

A computational model of current control mechanism for long-term potentiation (LTP) in human episodic memory based on gene-gene interaction

The establishment of long-term potentiation (LTP) is a prime process for the formation of episodic memory. During the establishment of LTP, activations of various components are required in the signaling cascade of the LTP pathway. Past efforts to determine the activation of components relied extensively on the cellular or molecular level. In this paper, we have proposed a computational model based on gene-level cascading and interaction in LTP signaling for the establishment and control of current signals for achieving the desired level of activation in the formation of episodic memory. This paper also introduces a model for a generalized signaling pathway in episodic memory. A back-propagation feedback mechanism is used for updating the interaction levels in the signaling cascade starting from the last stage and ending at the start stage of the signaling cascade. Simulation of the proposed model has been performed for the LTP signaling pathway in the context of human episodic memory. We found through simulation that the qualifying genes correction factors of all stages are updated to their maximum limit. The article explains the signaling pathway for episodic memory and proves its effectiveness through simulation results.

Post-ischemic ubiquitination at the postsynaptic density reversibly influences the activity of ischemia-relevant kinases

Ubiquitin modifications alter protein function and stability, thereby regulating cell homeostasis and viability, particularly under stress. Ischemic stroke induces protein ubiquitination at the ischemic periphery, wherein cells remain viable, however the identity of ubiquitinated proteins is unknown. Here, we employed a proteomics approach to identify these proteins in mice undergoing ischemic stroke. The data are available in a searchable web interface ( https://hochrainerlab.shinyapps.io/StrokeUbiOmics/ ). We detected increased ubiquitination of 198 proteins, many of which localize to the postsynaptic density (PSD) of glutamatergic neurons. Among these were proteins essential for maintaining PSD architecture, such as PSD95, as well as NMDA and AMPA receptor subunits. The largest enzymatic group at the PSD with elevated post-ischemic ubiquitination were kinases, such as CaMKII, PKC, Cdk5, and Pyk2, whose aberrant activities are well-known to contribute to post-ischemic neuronal death. Concurrent phospho-proteomics revealed altered PSD-associated phosphorylation patterns, indicative of modified kinase activities following stroke. PSD-located CaMKII, PKC, and Cdk5 activities were decreased while Pyk2 activity was increased after stroke. Removal of ubiquitin restored kinase activities to pre-stroke levels, identifying ubiquitination as the responsible molecular mechanism for post-ischemic kinase regulation. These findings unveil a previously unrecognized role of ubiquitination in the regulation of essential kinases involved in ischemic injury.

Electrophysiological Assessment of Newly Synthesized 2,3-Benzodiazepine Derivatives for Inhibiting the AMPA Receptor Channel

Three major subtypes of ionotropic receptors regulate glutamatergic synaptic transmission, one of which is α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPARs). They are tetrameric, cation-permeable ionotropic glutamate receptors found across the brain. Abnormalities in AMPA receptor trafficking and synaptic assembly are linked to cognitive decline and neurological diseases such as Alzheimer's, Parkinson's, and Huntington's. The present study will investigate the effects of four novel 2,3-benzodiazepine derivatives on AMPA receptor subunits by comparing their effects on synaptic responses, desensitization, and deactivation rate in human embryonic kidney cells (HEK293T) recombinant AMPAR subunits using whole-cell patch-clamp electrophysiology. All four 2,3-BDZ compounds showed inhibitory activity against all the homomeric and heteromeric subunits tested. While the desensitization and deactivation rates in 2,3-BDZ-1 and 2,3-BDZ-2 decreased and increased, respectively, in the other two compounds (i.e., 2,3-BDZ-3 and 2,3-BDZ-4), there was no change in the desensitization or deactivation rates. These results contribute to a better understanding of AMPARs by identifying potential 2,3-BDZ drugs that demonstrate inhibitory effects on the AMPAR subunits.

Calcium/Calmodulin-Stimulated Protein Kinase II (CaMKII): Different Functional Outcomes from Activation, Depending on the Cellular Microenvironment

Calcium/calmodulin-stimulated protein kinase II (CaMKII) is a family of broad substrate specificity serine (Ser)/threonine (Thr) protein kinases widely expressed in many tissues that is capable of mediating diverse functional responses depending on its cellular and molecular microenvironment. This review briefly summarises current knowledge on the structure and regulation of CaMKII and focuses on how the molecular environment, and interaction with binding partner proteins, can produce different populations of CaMKII in different cells, or in different subcellular locations within the same cell, and how these different populations of CaMKII can produce diverse functional responses to activation following an increase in intracellular calcium concentration. This review also explores the possibility that identifying and characterising the molecular interactions responsible for the molecular targeting of CaMKII in different cells in vivo, and identifying the sites on CaMKII and/or the binding proteins through which these interactions occur, could lead to the development of highly selective inhibitors of specific CaMKII-mediated functional responses in specific cells that would not affect CaMKII-mediated responses in other cells. This may result in the development of new pharmacological agents with therapeutic potential for many clinical conditions.

Protein kinase C mediates hypoxia-induced long-term potentiation of NMDA neurotransmission in the visual retinocollicular pathway

The identification of processes and mechanisms underlying the early stage of hypoxic injury of the retinocollicular pathway may be beneficial for the future prevention and treatment of navigation, orientation, and visual attention impairments. Previously, we have demonstrated that short-term hypoxia led to long-term potentiation (LTP) of NMDA neurotransmission in the background of long-term depression of GABA_A retinocollicular transmission. Here, we sought to obtain insight into the mechanisms of hypoxia-induced LTP of NMDA retinocollicular neurotransmission and the role of the protein kinase C (PKC) signaling pathway in it. To investigate these, we recorded pharmacologically isolated NMDA transmission in cocultivated pairs of rat retinal ganglion cells and superficial superior colliculus neurons under normoxic and hypoxic conditions, using the paired patch-clamp technique and method of fast local superfusion. We tested the involvement of the PKC by adding the potent and selective inhibitor chelerythrine chloride (ChC, 5 μM). We observed that hypoxia-induced LTP of NMDA neurotransmission is associated with the shortening of current kinetics. We also found that the PKC signaling pathway mediates hypoxia-induced LTP and associated shortening of NMDA currents. The ChC completely blocked the induction of LTP by hypoxia and associated kinetic changes. Contrary effects of ChC were observed with already induced LTP. ChC led to the reversal of LTP to the initial synaptic strength but the current kinetics remain irreversibly shortened. Our results show that ChC is a promising agent for the prevention and treatment of hypoxic injuries of NMDA retinocollicular neurotransmission and provide necessary electrophysiological basics for further research.

Calcium Signalling in Heart and Vessels: Role of Calmodulin and Downstream Calmodulin-Dependent Protein Kinases

Cardiovascular disease is the major cause of death worldwide. The success of medication and other preventive measures introduced in the last century have not yet halted the epidemic of cardiovascular disease. Although the molecular mechanisms of the pathophysiology of the heart and vessels have been extensively studied, the burden of ischemic cardiovascular conditions has risen to become a top cause of morbidity and mortality. Calcium has important functions in the cardiovascular system. Calcium is involved in the mechanism of excitation-contraction coupling that regulates numerous events, ranging from the production of action potentials to the contraction of cardiomyocytes and vascular smooth muscle cells. Both in the heart and vessels, the rise of intracellular calcium is sensed by calmodulin, a protein that regulates and activates downstream kinases involved in regulating calcium signalling. Among them is the calcium calmodulin kinase family, which is involved in the regulation of cardiac functions. In this review, we present the current literature regarding the role of calcium/calmodulin pathways in the heart and vessels with the aim to summarize our mechanistic understanding of this process and to open novel avenues for research.

Long-term maintenance of synaptic plasticity by Fullerenol Ameliorates lead-induced-impaired learning and memory in vivo

Fullerenol, a functional and water-soluble fullerene derivative, plays an important role in antioxidant, antitumor and antivirus, implying its enormous potential in biomedical applications. However, the in vivo performance of fullerenol remains largely unclear. We aimed to investigate the effect of fullerenol (i.p., 5 mg/kg) on the impaired hippocampus in a rat model of lead exposure. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is a kind of newly developed soft-ionization mass spectrometry technology. In the present study, an innovative strategy for biological distribution analysis using MALDI-TOF-MS confirmed that fullerenol could across the blood-brain barrier and accumulate in the brain. Results from behavioral tests showed that a low dose of fullerenol could improve the impaired learning and memory induced by lead. Furthermore, electrophysiology examinations indicated that this potential repair effect of fullerenol was mainly due to the long-term changes in hippocampal synaptic plasticity, with enhancement lasting for more than 2-3 h. In addition, morphological observations and biochemistry analyses manifested that the long-term change in synaptic efficacy was accompanied by some structural alteration in synaptic connection. Our study demonstrates the therapeutic feature of fullerenol will be beneficial to the discovery and development as a new drug and lays a solid foundation for further biomedical applications of nanomedicines.

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.

Identification and characterization of long non-coding RNA Carip in modulating spatial learning and memory

CaMKII has long been known to be a key effector for synaptic plasticity. Recent studies have shown that a variety of modulators interact with the subunits of CaMKII to regulate the long-term potentiation (LTP) of hippocampal neurons. However, whether long non-coding RNAs modulate the activity of CaMKII and affect synaptic plasticity is still elusive. Here, we identify a previously uncharacterized long non-coding RNA Carip that functions as a scaffold, specifically interacts with CaMKIIβ, and regulates the phosphorylation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) receptor subunits in the hippocampus. The absence of Carip causes dysfunction of synaptic transmission and attenuates LTP in hippocampal CA3-CA1 synapses, which further leads to impairment of spatial learning and memory. In summary, our findings demonstrate that Carip modulates long-term synaptic plasticity by changing AMPA receptor and NMDA receptor activities, thereby affecting spatial learning and memory in mice.

Behind the scenes: Are latent memories supported by calcium independent plasticity?

N-methyl-D-aspartate receptors (NMDARs) can be considered to be the de facto "plasticity" receptors in the brain due to their central role in the activity-dependent modification of neuronal morphology and synaptic transmission. Since the 1980s, research on NMDARs has focused on the second messenger properties of calcium and the downstream signaling pathways that mediate alterations in neural form and function. Recently, NMDARs were shown to drive activity-dependent synaptic plasticity without calcium influx. How this "nonionotropic" plasticity occurs in vitro is becoming clearer, but research on its involvement in behavior and cognition is in its infancy. There is a partial overlap in the downstream signaling molecules that are involved in ionotropic and nonionotropic NMDAR-dependent plasticity. Given this, and prior studies of the cognitive impacts of ionotropic NMDAR plasticity, a preliminary model explaining how NMDAR nonionotropic plasticity affects learning and memory can be established. We hypothesize that nonionotropic NMDAR plasticity takes part in latent memory encoding in immature rodents through nonassociative depression of synaptic efficacy, and possibly shrinking of dendritic spines. Further, the late postnatal alteration in NMDAR composition in the hippocampus appears to reduce nonionotropic signaling and remove a restriction on memory retrieval. This framework substantially alters the canonical model of NMDAR involvement in spatial cognition and hippocampal maturation and provides novel and exciting inroads for future studies.

A framework for preparing a stochastic nonlinear integrate-and-fire model for integrated information theory

This paper presents a framework for spiking neural networks to be prepared for the Integrated Information Theory (IIT) analysis, using a stochastic nonlinear integrate-and-fire model. The model includes the crucial dynamics of the all-or-none law and after-spike refractoriness. The noise is modelled as an additive term in the system's equations. By preparing the model for the IIT analysis, it is meant to determine the length of the analysis time-window and the transition probability distributions required for the IIT 3.0. To this end, a system of differential equations is proposed to estimate the time evolution of the system's mean and covariance. Assuming the binary Fired/Silent activity as the possible states of each neuron, an algorithm is proposed to calculate the required probability distributions. As long as the Fired/Silent probabilities are only concerned, the Gaussian density assumption with the estimated moments is a reasonable estimate. The synaptic inputs are treated as random variables with low variances to avoid the costs of conditioning on the system's past activities. The Monte-Carlo simulation is used to validate the estimation methods. To increase the reliability of the inductive inference behind the Monte-Carlo method, various stimulation protocols are applied to evoke the dynamics of the equations.

Sea Cucumber Peptides Attenuated the Scopolamine-Induced Memory Impairment in Mice and Rats and the Underlying Mechanism

Social stress and unhealthy diets lead to memory impairment, triggering health problems. This study aimed to determine the mitigating effect and regulation mechanism of sea cucumber peptides (SCP) against memory impairment. Here, scopolamine-induced memory impairment in mouse and rat models was used based on behavioral tests, a histological staining technique, Fourier transform infrared microscopy, and gas-chromatographic analysis as well as a Western blotting method. SCP improved the behavioral performance and regulated the disorder of the cholinergic system in mouse models in a dose-dependent manner. Therefore, the underlying mechanism was explored in high-dose SCP using mouse and rat models. SCP repaired damaged neuronal cells, enhanced the Nissl body number, increased the unsaturated lipid level, and activated the long-term potentiation (LTP) pathway (p-CaMKII, p-CREB, and BDNF), both in the mouse and rat hippocampus. The results indicated that SCP upregulated the LTP pathway and unsaturated lipid level to combat scopolamine-induced memory impairment, suggesting that SCP was a potential candidate for neurological recovery.

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.

Comprehensive Analysis of Mouse Hippocampal Lysine Acetylome Mediated by Sea Cucumber Peptides Preventing Memory Impairment

Memory impairment is becoming a potential health issue with the delicacy of diet and social stress. Sea cucumber peptides (SCP) prevent memory impairment, as previously reported. In this study, further research was performed using hippocampal lysine-acetylome to explore molecular regulation mechanisms. C57BL/6 mice were treated with scopolamine via intraperitoneal injection to simulate memory impairment. To determine the influence of SCP on the total acetylated-protein level of the hippocampus, acetylated-proteomics was performed. SCP increased the acetylation level of histone (H3 and H4). Meanwhile, for non-histones, the differentially acetylated proteins were involved in multiple memory-related pathways, as shown by KEGG enrichment analysis. Additionally, long-term potentiation was confirmed by western blotting. Finally, a combined analysis of proteome and lysine acetylome revealed that SCP contributed to synaptic vesicle cycle regulation and dopamine metabolism. Consequently, our findings revealed that SCP was potentially neuroprotective by regulating post-transcriptional hippocampal protein acetylation.

Calmodulin as Ca2+-Dependent Interactor of FTO Dioxygenase

FTO is an N⁶-methyladenosine demethylase removing methyl groups from nucleic acids. Several studies indicate the creation of FTO complexes with other proteins. Here, we looked for regulatory proteins recognizing parts of the FTO dioxygenase region. In the Calmodulin (CaM) Target Database, we found the FTO C-domain potentially binding CaM, and we proved this finding experimentally. The interaction was Ca²⁺-dependent but independent on FTO phosphorylation. We found that FTO–CaM interaction essentially influences calcium-binding loops in CaM, indicating the presence of two peptide populations—exchanging as CaM alone and differently, suggesting that only one part of CaM interacts with FTO, and the other one reminds free. The modeling of FTO–CaM interaction showed its stable structure when the half of the CaM molecule saturated with Ca²⁺ interacts with the FTO C-domain, whereas the other part is disconnected. The presented data indicate calmodulin as a new FTO interactor and support engagement of the FTO protein in calcium signaling pathways.

Cortical layer-specific modulation of neuronal activity after sensory deprivation due to spinal cord injury

Abstract

Cortical areas have the capacity of large‐scale reorganization following sensory deafferentation. However, it remains unclear whether this phenomenon is a unique process that homogeneously affects the entire deprived cortical region or whether it is susceptible to changes depending on neuronal networks across distinct cortical layers. Here, we studied how the local circuitry within each layer of the deafferented cortex forms the basis for neuroplastic changes after immediate thoracic spinal cord injury (SCI) in anaesthetized rats. In vivo electrophysiological recordings from deafferented hindlimb somatosensory cortex showed that SCI induces layer‐specific changes mediating evoked and spontaneous activity. In supragranular layer 2/3, SCI increased gamma oscillations and the ability of these neurons to initiate up‐states during spontaneous activity, suggesting an altered corticocortical network and/or intrinsic properties that may serve to maintain the excitability of the cortical column after deafferentation. On the other hand, SCI enhanced the infragranular layers’ ability to integrate evoked sensory inputs leading to increased and faster neuronal responses. Delayed evoked response onsets were also observed in layer 5/6, suggesting alterations in thalamocortical connectivity. Altogether, our data indicate that SCI immediately modifies the local circuitry within the deafferented cortex allowing supragranular layers to better integrate spontaneous corticocortical information, thus modifying column excitability, and infragranular layers to better integrate evoked sensory inputs to preserve subcortical outputs. These layer‐specific neuronal changes may guide the long‐term alterations in neuronal excitability and plasticity associated with the rearrangements of somatosensory networks and the appearance of central sensory pathologies usually associated with spinal cord injury.

Key points

Sensory stimulation of forelimb produces cortical evoked responses in the somatosensory hindlimb cortex in a layer‐dependent manner.

Spinal cord injury favours the input statistics of corticocortical connections between intact and deafferented cortices.

After spinal cord injury supragranular layers exhibit better integration of spontaneous corticocortical information while infragranular layers exhibit better integration of evoked sensory stimulation.

Cortical reorganization is a layer‐specific phenomenon.

SRC3 acetylates calmodulin in the mouse brain to regulate synaptic plasticity and fear learning

Protein acetylation is a reversible posttranslational modification, which is regulated by lysine acetyltransferase (KAT) and lysine deacetyltransferase (KDAC). Although protein acetylation has been shown to regulate synaptic plasticity, this was mainly for histone protein acetylation. The function and regulation of nonhistone protein acetylation in synaptic plasticity and learning remain largely unknown. Calmodulin (CaM), a ubiquitous Ca²⁺ sensor, plays critical roles in synaptic plasticity such as long-term potentiation (LTP). During LTP induction, activation of NMDA receptor triggers Ca²⁺ influx, and the Ca²⁺ binds with CaM and activates calcium/calmodulin-dependent protein kinase IIα (CaMKIIα). In our previous study, we demonstrated that acetylation of CaM was important for synaptic plasticity and fear learning in mice. However, the KAT responsible for CaM acetylation is currently unknown. Here, following an HEK293 cell-based screen of candidate KATs, steroid receptor coactivator 3 (SRC3) is identified as the most active KAT for CaM. We further demonstrate that SRC3 interacts with and acetylates CaM in a Ca²⁺ and NMDA receptor-dependent manner. We also show that pharmacological inhibition or genetic downregulation of SRC3 impairs CaM acetylation, synaptic plasticity, and contextual fear learning in mice. Moreover, the effects of SRC3 inhibition on synaptic plasticity and fear learning could be rescued by 3KQ-CaM, a mutant form of CaM, which mimics acetylation. Together, these observations demonstrate that SRC3 acetylates CaM and regulates synaptic plasticity and learning in mice.

Acetylation of calmodulin regulates synaptic plasticity and fear learning

Synaptic plasticity is critical for brain function, including learning and memory. It is regulated by gene transcription and protein synthesis as well as posttranslational modifications at synapses. Although protein acetylation has been shown to be involved in the regulation of synaptic plasticity, this was mainly for histone protein acetylation. To investigate whether acetylation of nonhistone proteins is important for synaptic plasticity, we analyzed mouse brain acetylome and found that calmodulin (CaM), a ubiquitous Ca²⁺ sensor, was acetylated on three lysine residues, which were conserved across species. NMDA receptor-dependent long-term potentiation (LTP) is considered the most compelling form of synaptic plasticity. During LTP induction, activation of NMDA receptor triggers Ca²⁺ influx, and the Ca²⁺ binds with CaM and activates calcium/calmodulin-dependent protein kinase IIα (CaMKIIα), which is essential for LTP induction. By using home-generated and site-specific antibodies against acetylated CaM, we show that CaM acetylation is upregulated by neural activities in an NMDA receptor-dependent manner. Moreover, mutation of acetyllysines in CaM1 proteins disrupts synaptic plasticity and fear learning in a mouse model. We further demonstrate that acetylation of CaM reduces the binding free energy and increases the binding affinity toward CaMKIIα, a protein kinase pivotal to synaptic plasticity and learning. Taken together, our results demonstrate importance of CaM acetylation in regulating synaptic plasticity and learning.

Convergent NMDA receptor-Pannexin1 signaling pathways regulate the interaction of CaMKII with Connexin-36

Ca2+/calmodulin-dependent protein kinase II (CaMKII) binding and phosphorylation of mammalian connexin-36 (Cx36) potentiate electrical coupling. To explain the molecular mechanism of how Cx36 modifies plasticity at gap junctions, we investigated the roles of ionotropic N-methyl-D-aspartate receptors and pannexin1 (Panx1) channels in regulating Cx36 binding to CaMKII. Pharmacological interference and site-directed mutagenesis of protein interaction sites shows that NMDA receptor activation opens Cx36 channels, causing the Cx36- CaMKII binding complex to adopt a compact conformation. Ectopic Panx1 expression in a Panx1 knock-down cell line is required to restore CaMKII mediated opening of Cx36. Furthermore, blocking of Src-family kinase activation of Panx1 is sufficient to prevent the opening of Cx36 channels. Our research demonstrates that the efficacy of Cx36 channels requires convergent calcium-dependent signaling processes in which activation of ionotropic N-methyl-D-aspartate receptor, Src-family kinase, and Pannexin1 open Cx36. Our results add to the best of our knowledge a new twist to mounting evidence for molecular communication between these core components of electrical and chemical synapses.

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.

Compartmentalized Signaling in Aging and Neurodegeneration

The cyclic AMP (cAMP) signalling cascade is necessary for cell homeostasis and plays important roles in many processes. This is particularly relevant during ageing and age-related diseases, where drastic changes, generally decreases, in cAMP levels have been associated with the progressive decline in overall cell function and, eventually, the loss of cellular integrity. The functional relevance of reduced cAMP is clearly supported by the finding that increases in cAMP levels can reverse some of the effects of ageing. Nevertheless, despite these observations, the molecular mechanisms underlying the dysregulation of cAMP signalling in ageing are not well understood. Compartmentalization is widely accepted as the modality through which cAMP achieves its functional specificity; therefore, it is important to understand whether and how this mechanism is affected during ageing and to define which is its contribution to this process. Several animal models demonstrate the importance of specific cAMP signalling components in ageing, however, how age-related changes in each of these elements affect the compartmentalization of the cAMP pathway is largely unknown. In this review, we explore the connection of single components of the cAMP signalling cascade to ageing and age-related diseases whilst elaborating the literature in the context of cAMP signalling compartmentalization.

Maternal High-Fat Diet Multigenerationally Impairs Hippocampal Synaptic Plasticity and Memory in Male Rat Offspring

As advances are made in the field of developmental origins of health and disease, there is an emphasis on long-term influence of maternal environmental factors on offspring health. Maternal high-fat diet (HFD) consumption has been suggested to exert detrimental effects on cognitive function in offspring, but whether HFD-dependent brain remodeling can be transmitted to the next generations is still unclear. This study tested the hypothesis that HFD consumption during rat pregnancy and lactation multigenerationally influences male offspring hippocampal synaptic plasticity and cognitive function. We observed that hippocampus-dependent learning and memory was impaired in 3 generations from HFD-fed maternal ancestors (referred as F1-F3), as assessed by novel object recognition and Morris water maze tests. Moreover, maternal HFD exposure also affected electrophysiological and ultrastructure measures of hippocampal synaptic plasticity across generations. We observed that intranasal insulin replacement partially rescued hippocampal synaptic plasticity and cognitive deficits in F3 rats, suggesting central insulin resistance may play an important role in maternal diet-induced neuroplasticity impairment. Furthermore, maternal HFD exposure enhanced the palmitoylation of GluA1 critically involved in long-term potentiation induction, while palmitoylation inhibitor 2-bromopalmitate counteracts GluA1 hyperpalmitoylation and partially abolishes the detrimental effects of maternal diet on learning and memory in F3 offspring. Importantly, maternal HFD-dependent GluA1 hyperpalmitoylation was reversed by insulin replacement. Taken together, our data suggest that maternal HFD exposure multigenerationally influences adult male offspring hippocampal synaptic plasticity and cognitive performance, and central insulin resistance may serve as the cross-talk between maternal diet and cognitive impairment across generations.

Apelin-13 prevents hippocampal synaptic plasticity impairment in Parkinsonism rats

The hippocampus is involved in learning and memory for novel information and implicated within the cognitive dysfunction in Parkinson's disease. Long-term potentiation (LTP), the most type of synaptic plasticity, is the base of learning and memory. We evaluated the consequences of apelin-13 on early long-term potentiation (E-LTP) in the Cornu Ammonis (CA1) area of the hippocampus and synaptic hippocampal protein expression of postsynaptic density protein 95 (PSD-95) and dopaminergic receptor (DR1) of the rat model of Parkinsonism. 6-hydroxydopamine (6-OHDA) was infused within the right substantia nigra. Intra-nigral transfusion of apelin-13 (1, 2, and 3 μg/rat) was performed one week after the 6-OHDA injection. Using hematoxylin and eosin staining, the pathological changes in the substantia nigra neurons were examined. In Vivo field excitatory postsynaptic potentials were recorded in the CA1 region one month after the apelin injection. The PSD-95 and DR1 protein levels were assessed by western blotting. The mRNA expression level of DR1 was also measured by real-time PCR. 6-OHDA meaningfully disrupted short-term memory and LTP, and altered the expression levels of the above-mentioned proteins in the hippocampus. The results suggest that apelin-13 (especially at 3 μg/rat) significantly ameliorates the E-LTP impairment and attenuates the changes in hippocampal synaptic proteins in 6-OHDA-treated rats.

Coordination between Calcium/Calmodulin-Dependent Protein Kinase II and Neuronal Nitric Oxide Synthase in Neurons

Ca²⁺/calmodulin (CaM)-dependent protein kinase II (CaMKII) is highly abundant in the brain and exhibits broad substrate specificity, thereby it is thought to participate in the regulation of neuronal death and survival. Nitric oxide (NO), produced by neuronal NO synthase (nNOS), is an important neurotransmitter and plays a role in neuronal activity including learning and memory processes. However, high levels of NO can contribute to excitotoxicity following a stroke and neurodegenerative disease. Aside from NO, nNOS also generates superoxide which is involved in both cell injury and signaling. CaMKII is known to activate and translocate from the cytoplasm to the post-synaptic density in response to neuronal activation where nNOS is predominantly located. Phosphorylation of nNOS at Ser847 by CaMKII decreases NO generation and increases superoxide generation. Conversely, NO-induced S-nitrosylation of CaMKII at Cys6 is a prominent determinant of the CaMKII inhibition in ATP competitive fashion. Thus, the "cross-talk" between CaMKII and NO/superoxide may represent important signal transduction pathways in brain. In this review, we introduce the molecular mechanism of and pathophysiological role of mutual regulation between CaMKII and nNOS in neurons.

Phosphorylation Hypothesis of Sleep

Sleep is a fundamental property conserved across species. The homeostatic induction of sleep indicates the presence of a mechanism that is progressively activated by the awake state and that induces sleep. Several lines of evidence support that such function, namely, sleep need, lies in the neuronal assemblies rather than specific brain regions and circuits. However, the molecular mechanism underlying the dynamics of sleep need is still unclear. This review aims to summarize recent studies mainly in rodents indicating that protein phosphorylation, especially at the synapses, could be the molecular entity associated with sleep need. Genetic studies in rodents have identified a set of kinases that promote sleep. The activity of sleep-promoting kinases appears to be elevated during the awake phase and in sleep deprivation. Furthermore, the proteomic analysis demonstrated that the phosphorylation status of synaptic protein is controlled by the sleep-wake cycle. Therefore, a plausible scenario may be that the awake-dependent activation of kinases modifies the phosphorylation status of synaptic proteins to promote sleep. We also discuss the possible importance of multisite phosphorylation on macromolecular protein complexes to achieve the slow dynamics and physiological functions of sleep in mammals.

The role of dopamine D2-like receptors in a "depotentiation-like effect" of deep brain stimulation in kindled rats

The mechanisms involved in the anti-seizure effects of low-frequency stimulation (LFS) have not been completely determined. However, G_i-protein-coupled receptors, including D₂-like receptors, may have a role in mediating these effects. In the present study, the role of D₂-like receptors in LFS' anti-seizure action was investigated. Rats were kindled with semi-rapid (6 stimulations per day), electrical stimulation of the hippocampal CA1 area. In LFS-treated groups, subjects received four trials of LFS at 5 min, 6 h, 24 h, and 30 h following the last kindling stimulation. Each LFS set occurred at 5 min intervals, and consisted of 4 trains. Each train contained 200, 0/1 ms long, monophasic square wave pulses at 1 Hz. Haloperidol (D₂-like receptors antagonist, 2 µm) and/or bromocriptine (D₂-like receptors agonist 2 µg/µlit) were microinjected into the lateral ventricle immediately after the last kindling, before applying LFS. Obtained results showed that applying LFS in fully-kindled subjects led to a depotentiation-like decrease in kindling-induced potentiation and reduced the amplitude and rise slope of excitatory and inhibitory post-synaptic currents in whole-cell recordings from CA1 pyramidal neurons. In addition, LFS restored the kindling-induced, spatial learning and memory impairments in the Barnes maze test. A D₂-like receptor antagonist inhibited these effects of LFS, while a D₂-like receptor agonist mimicked these effects. In conclusion, a depotentiation-like mechanism may be involved in restoring LFS' effects on learning and memory, and synaptic plasticity. These effects depend on D₂-like receptors activity.

Calcium Dynamics and Synaptic Plasticity

Synaptic plasticity is a fundamental property of neurons referring to the activity-dependent changes in the strength and efficacy of synaptic transmission at preexisting synapses. Such changes can last from milliseconds to hours, days, or even longer and are involved in learning and memory as well as in development and response of the brain to injuries. Several types of synaptic plasticity have been described across neuronal types, brain regions, and species, but all of them share in one way or another capital importance of Ca²⁺-mediated processes. In this chapter, we will focus on the Ca²⁺-dependent events necessary for the induction and expression of multiple forms of synaptic plasticity.

Regulation of Multifunctional Calcium/Calmodulin Stimulated Protein Kinases by Molecular Targeting

Multifunctional calcium/calmodulin-stimulated protein kinases control a broad range of cellular functions in a multitude of cell types. This family of kinases contain several structural similarities and all are regulated by phosphorylation, which either activates, inhibits or modulates their kinase activity. As these protein kinases are widely or ubiquitously expressed, and yet regulate a broad range of different cellular functions, additional levels of regulation exist that control these cell-specific functions. Of particular importance for this specificity of function for multifunctional kinases is the expression of specific binding proteins that mediate molecular targeting. These molecular targeting mechanisms allow pools of kinase in different cells, or parts of a cell, to respond differently to activation and produce different functional outcomes.

Deep brain stimulation restores the glutamatergic and GABAergic synaptic transmission and plasticity to normal levels in kindled rats

Background

The precise effect of low frequency stimulation (LFS) as a newly postulated, anticonvulsant therapeutic approach on seizure-induced changes in synaptic transmission has not been completely determined.

Hypothesis

In this study, the LFS effect on impaired, synaptic plasticity in kindled rats was investigated.

Methods

Hippocampal kindled rats received LFS (4 trials consisting of one train of 200 monophasic square waves, 0.1 ms pulse duration, 1 Hz) on four occasions. LTP induction was evaluated using whole-cell recordings of evoked excitatory and inhibitory post-synaptic potentials (EPSPs and IPSPs respectively) in CA1 neurons in hippocampal slices. In addition, the hippocampal excitatory and inhibitory post-synaptic currents (EPSCs and IPSCs), and the gene expression of NR₂A, GluR₂ and γ₂ were evaluated.

Results

LTP induction was attenuated in excitatory and inhibitory synapses in hippocampal slices of kindled rats. When LFS was applied in kindled animals, LTP was induced in EPSPs and IPSPs. Moreover, LFS increased and decreased the threshold intensities of EPSCs and IPSCs respectively. In kindled animals, NR₂A gene expression increased, while γ₂ gene expression decreased. GluR2 gene expression did not significantly change. Applying LFS in kindled animals mitigated these changes: No significant differences were observed in NR₂A, γ₂ and GluR₂ gene expression in the kindled+LFS and control groups.

Conclusion

The application of LFS in kindled animals restored LTP induction in both EPSPs and IPSPs, and returned the threshold intensity for induction of EPSCs, IPSCs and gene expression to similar levels as controls.

Degeneracy in hippocampal physiology and plasticity

Degeneracy, defined as the ability of structurally disparate elements to perform analogous function, has largely been assessed from the perspective of maintaining robustness of physiology or plasticity. How does the framework of degeneracy assimilate into an encoding system where the ability to change is an essential ingredient for storing new incoming information? Could degeneracy maintain the balance between the apparently contradictory goals of the need to change for encoding and the need to resist change towards maintaining homeostasis? In this review, we explore these fundamental questions with the mammalian hippocampus as an example encoding system. We systematically catalog lines of evidence, spanning multiple scales of analysis that point to the expression of degeneracy in hippocampal physiology and plasticity. We assess the potential of degeneracy as a framework to achieve the conjoint goals of encoding and homeostasis without cross-interferences. We postulate that biological complexity, involving interactions among the numerous parameters spanning different scales of analysis, could establish disparate routes towards accomplishing these conjoint goals. These disparate routes then provide several degrees of freedom to the encoding-homeostasis system in accomplishing its tasks in an input- and state-dependent manner. Finally, the expression of degeneracy spanning multiple scales offers an ideal reconciliation to several outstanding controversies, through the recognition that the seemingly contradictory disparate observations are merely alternate routes that the system might recruit towards accomplishment of its goals.

A Single Session of Aerobic Exercise Mediates Plasticity-Related Phosphorylation in both the Rat Motor Cortex and Hippocampus

A single session of aerobic exercise may offer one means to "prime" motor regions to be more receptive to the acquisition of a motor skill; however, the mechanisms whereby this priming may occur are not clear. One possible explanation may be related to the post-translational modification of plasticity-related receptors and their associated intracellular signaling molecules, given that these proteins are integral to the development of synaptic plasticity. In particular, phosphorylation governs the biophysical properties (e.g., Ca²⁺ conductance) and the migratory patterns (i.e., trafficking) of plasticity-related receptors by altering the relative density of specific receptor subunits at synapses. We hypothesized that a single session of exercise would alter the subunit phosphorylation of plasticity-related receptors (AMPA receptors, NMDA receptors) and signaling molecules (PKA, CaMKII) in a manner that would serve to prime motor cortex. Young, male Sprague-Dawley rats (n = 24) were assigned to either exercise (Moderate, Exhaustion), or non-exercising (Sedentary) groups. Immediately following a single session of treadmill exercise, whole tissue homogenates were prepared from both the motor cortex and hippocampus. We observed a robust (1.2-2.0× greater than sedentary) increase in tyrosine phosphorylation of AMPA (GluA1,2) and NMDA (GluN2A,B) receptor subunits, and a clear indication that exercise preferentially affects pPKA over pCaMKII. The changes were found, specifically, following moderate, but not maximal, acute aerobic exercise in both motor cortex and hippocampus. Given the requirement for these proteins during the early phases of plasticity induction, the possibility exists that exercise-induced priming may occur by altering the phosphorylation of plasticity-related proteins.

Electron Acceptive Mass Tag for Mass Spectrometric Imaging-Guided Synergistic Targeting to Mice Brain Glutamate Receptors

Dysfunctional glutamate receptors (GluRs) have been implicated in neurological disorders and injuries. Hetero-tetrameric assemblies of different GluR subunits or splicing variants have distinct spatiotemporal expression patterns and pharmacological properties. Mass spectrometric imaging of GluRs-targeted small molecules is important for determining the regional preferences of these compounds. We report herein the development of a mass tag covalently bonded with glutamate or N-methyl-d-aspartate that functions as both an electron acceptor to generate mass spectrometric signals on irradiated (Bi₂O₃)_0.07(CoO)_0.03(ZnO)_0.9 nanoparticles with the third harmonic (355 nm) of Nd³⁺:YAG laser and as the core component to target bilobed clamshell-like structures of GluRs. In this approach, different molecules produce the same tag ion. It provides a new avenue for quantitative assessment of spatial densities of different compounds, which cannot be achieved with well-established stable isotope labeling technique due to different ionization efficiency of different compounds. Various coexisting endogenous molecules are also simultaneously detected for investigation of overall physiological changes induced by these compounds. Because semiconductors do not generate background peaks, this method eliminates interferences from organic matrix materials that are used in regular MALDI (matrix assisted laser desorption ionization). The localized ionization provides high spatial resolution that can be down to sub-micrometers.

The Multi-Functional Calcium/Calmodulin Stimulated Protein Kinase (CaMK) Family: Emerging Targets for Anti-Cancer Therapeutic Intervention

The importance of Ca²⁺ signalling in key events of cancer cell function and tumour progression, such as proliferation, migration, invasion and survival, has recently begun to be appreciated. Many cellular Ca²⁺-stimulated signalling cascades utilise the intermediate, calmodulin (CaM). The Ca²⁺/CaM complex binds and activates a variety of enzymes, including members of the multifunctional Ca²⁺/calmodulin-stimulated protein kinase (CaMK) family. These enzymes control a broad range of cancer-related functions in a multitude of tumour types. Herein, we explore the cancer-related functions of these kinases and discuss their potential as targets for therapeutic intervention.

Animal Models of Self-Injurious Behavior: An Update

Although self-injurious behavior is a common comorbid behavior problem among individuals with neurodevelopmental disorders, little is known about its etiology and underlying neurobiology. Interestingly, it shows up in various forms across patient groups with distinct genetic errors and diagnostic categories. This suggests that there may be shared neuropathology that confers vulnerability in these disparate groups. Convergent evidence from clinical pharmacotherapy, brain imaging studies, postmortem neurochemical analyses, and animal models indicates that dopaminergic insufficiency is a key contributing factor. This chapter provides an overview of studies in which animal models have been used to investigate the biochemical basis of self-injury and highlights the convergence in findings between these models and expression of self-injury in humans.

Loren Parsons' contribution to addiction neurobiology

Loren (Larry) H. Parsons passed away at the age of 51. In spite of his premature departure, Larry much contributed to the drug abuse field. Since his graduate studies for the Ph.D. in Chemistry in J.B. Justice lab, microdialysis is the tread that links Larry's research topics, namely, the role of dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), glutamate and endocannabinoids (eCBs) in drug reinforcement and dependence. Larry was the first to show that abstinence from chronic cocaine reduces extracellular DA in the NAc, consistent with the so called 'dopamine depletion hypothesis' of cocaine addiction. Another Larry's major contributions are the studies on 5-HT and 5-HT receptors' role in cocaine stimulant actions, which resulted in the identification of 5-HT1B receptors as a critical substrate of cocaine reinforcement. By applying mass spectrometry to eCBs analysis in brain dialysates, Larry's lab showed that ethanol, heroin, nicotine and cocaine differentially affect anandamide and 2-arachidonoylglicerol overflow in the NAc shell, a critical site of drugs of abuse DA stimulant actions. Larry also applied microdialysis to study GABA and glutamate's role in ethanol dependence and heroin reinforcement, providing in vivo evidence for a sensitization of corticotropin-releasing factor-dependent release of GABA in the central amygdala in withdrawal from chronic ethanol and for a reduction of GABA transmission in the ventral pallidum in heroin but not cocaine intravenous self-administration. Larry showed the wide possibilities of microdialysis as a general purpose methodology for monitoring neurotransmitters and neuromodulators in the brain extracellular compartment. From this viewpoint, he stands as the best advocate for microdialysis.

Activation of TRPV1 receptors affects memory function and hippocampal TRPV1 and CREB mRNA expression in a rat model of biliary cirrhosis

OBJECTIVE

Memory impairment induced by biliary cirrhosis is associated with abnormalities in the function of different neurotransmitter systems. However, the exact molecular mechanisms involved in the learning and memory dysfunctions following biliary cirrhosis is largely unknown. This study set out to determine whether activation of transient receptor potential vanilloid type 1 (TRPV1) in the CA1 area of the hippocampus in rats improve memory impairment induced by biliary cirrhosis.

METHODS

To assess learning and memory, passive avoidance task was carried out using a shuttle box. The mRNA expression of TRPV1 and cAMP response element binding (CREB) protein in the hippocampus were also evaluated by qT-PCR.

RESULTS

Our results indicated that activation of TRPV1 channels by capsaicin significantly decreased memory impairment and increased mRNA expression of the TRPV1 and CREB in the hippocampus of rats with biliary cirrhosis. Our findings also demonstrated that a positive correlation existed between mRNA expression of TRPV1 and CREB, and between memory function and TRPV1 expression.

DISCUSSION

Taken together, the results of this study support the view that TRPV1 receptor may play an important role in the regulation of learning and memory functions, and suggest that activation of TRPV1 channels seems to be a promising therapeutic target for learning and memory impairments following biliary cirrhosis.

Phosphorylation of calcium/calmodulin-dependent protein kinase II in the rat dorsal medial prefrontal cortex is associated with alcohol-induced cognitive inflexibility

Repeated cycles of alcohol [ethanol (EtOH)] intoxication and withdrawal dysregulate excitatory glutamatergic systems in the brain and induce neuroadaptations in the medial prefrontal cortex (mPFC) that contribute to cognitive dysfunction. The mPFC is composed of subdivisions that are functionally distinct, with dorsal regions facilitating drug-cue associations and ventral regions modulating new learning in the absence of drug. A key modulator of glutamatergic activity is the holoenzyme calcium/calmodulin-dependent protein kinase II (CaMKII) that phosphorylates ionotropic glutamate receptors. Here, we examined the hypothesis that abstinence from chronic intermittent EtOH (CIE) exposure dysregulates CaMKII activity in the mPFC to impair cognitive flexibility. We used an operant model of strategy set shifting in male Long-Evans rats demonstrating reduced susceptibility to trial omissions during performance in a visual cue-guided task versus albino strains. Relative to naïve controls, rats experiencing approximately 10 days of abstinence from CIE vapor exposure demonstrated impaired performance during a procedural shift from visual cue to spatial location discrimination. Phosphorylation of CaMKII subtype α was upregulated in the dorsal, but not ventral mPFC of CIE-exposed rats, and was positively correlated with perseverative-like responding during the set shift. The findings suggest that abstinence from CIE exposure induces an undercurrent of kinase activity (e.g. CaMKII), which may promote aberrant glutamatergic responses in select regions of the mPFC. Given the role of the mPFC in modulating executive control of behavior, we propose that increased CaMKII subtype α activity reflects a dysregulated 'top-down' circuit that interferes with adaptive behavioral performance under changing environmental demands.

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

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

Brain insulin resistance impairs hippocampal synaptic plasticity and memory by increasing GluA1 palmitoylation through FoxO3a

High-fat diet (HFD) and metabolic diseases cause detrimental effects on hippocampal synaptic plasticity, learning, and memory through molecular mechanisms still poorly understood. Here, we demonstrate that HFD increases palmitic acid deposition in the hippocampus and induces hippocampal insulin resistance leading to FoxO3a-mediated overexpression of the palmitoyltransferase zDHHC3. The excess of palmitic acid along with higher zDHHC3 levels causes hyper-palmitoylation of AMPA glutamate receptor subunit GluA1, hindering its activity-dependent trafficking to the plasma membrane. Accordingly, AMPAR current amplitudes and, more importantly, their potentiation underlying synaptic plasticity were inhibited, as well as hippocampal-dependent memory. Hippocampus-specific silencing of Zdhhc3 and, interestingly enough, intranasal injection of the palmitoyltransferase inhibitor, 2-bromopalmitate, counteract GluA1 hyper-palmitoylation and restore synaptic plasticity and memory in HFD mice. Our data reveal a key role of FoxO3a/Zdhhc3/GluA1 axis in the HFD-dependent impairment of cognitive function and identify a novel mechanism underlying the cross talk between metabolic and cognitive disorders.

Soluble Epoxide Hydrolase Inhibitor and 14,15-Epoxyeicosatrienoic Acid-Facilitated Long-Term Potentiation through cAMP and CaMKII in the Hippocampus

Epoxyeicosatrienoic acids (EETs) are derived from arachidonic acid and metabolized by soluble epoxide hydrolase (sEH). The role of EETs in synaptic function in the central nervous system is still largely unknown. We found that pharmacological inhibition of sEH to stabilize endogenous EETs and exogenous 14,15-EET significantly increased the field excitatory postsynaptic potential (fEPSP) response in the CA1 area of the hippocampus, while additionally enhancing high-frequency stimulation- (HFS-) induced long-term potentiation (LTP) and forskolin- (FSK-) induced LTP. sEH inhibitor (sEHI) N-[1-(oxopropyl)-4-piperidinyl]-N'-[4-(trifluoromethoxy) phenyl)-urea (TPPU) and exogenous 14,15-EET increased HFS-LTP, which could be blocked by an N-methyl-D-aspartate (NMDA) receptor subunit NR2B antagonist. TPPU- or 14,15-EET-facilitated FSK-mediated LTP can be potentiated by an A1 adenosine receptor antagonist and a phosphodiesterase inhibitor, but is prevented by a cAMP-dependent protein kinase (PKA) inhibitor. sEHI and 14,15-EET upregulated the activation of extracellular signal-regulated kinases (ERKs) and Ca2+/calmodulin- (CaM-) dependent protein kinase II (CaMKII). Phosphorylation of synaptic receptors NR2B and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluR1 was increased by TPPU and 14,15-EET administration. These results indicated that EETs increased NMDAR- and FSK-mediated synaptic potentiation via the AC-cAMP-PKA signaling cascade and upregulated the ERKs and CaMKII, resulting in increased phosphorylation of NR2B and GluR1 in the hippocampus.