M1-muscarinic receptors promote fear memory consolidation via phospholipase C and the M-current

PKCδ is an activator of neuronal mitochondrial metabolism that mediates the spacing effect on memory consolidation

Relevance-based selectivity and high energy cost are two distinct features of long-term memory (LTM) formation that warrant its default inhibition. Spaced repetition of learning is a highly conserved cognitive mechanism that can lift this inhibition. Here, we questioned how the spacing effect integrates experience selection and energy efficiency at the cellular and molecular levels. We showed in Drosophila that spaced training triggers LTM formation by extending over several hours an increased mitochondrial metabolic activity in neurons of the associative memory center, the mushroom bodies (MBs). We found that this effect is mediated by PKCδ, a member of the so-called 'novel PKC' family of enzymes, which uncovers the critical function of PKCδ in neurons as a regulator of mitochondrial metabolism for LTM. Additionally, PKCδ activation and translocation to mitochondria result from LTM-specific dopamine signaling on MB neurons. By bridging experience-dependent neuronal circuit activity with metabolic modulation of memory-encoding neurons, PKCδ signaling binds the cognitive and metabolic constraints underlying LTM formation into a unified gating mechanism.

A light-controlled phospholipase C for imaging of lipid dynamics and controlling neural plasticity

Phospholipase C (PLC) is a key enzyme that regulates physiological processes via lipid and calcium signaling. Despite advances in protein engineering, no tools are available for direct PLC control. Here, we developed a novel optogenetic tool, light-controlled PLCβ (opto-PLCβ). Opto-PLCβ uses a light-induced dimer module, which directs an engineered PLC to the plasma membrane in a light-dependent manner. Our design includes an autoinhibitory capacity, ensuring stringent control over PLC activity. Opto-PLCβ triggers reversible calcium responses and lipid dynamics in a restricted region, allowing precise spatiotemporal control of PLC signaling. Using our system, we discovered that phospholipase D-mediated phosphatidic acid contributes to diacylglycerol clearance on the plasma membrane. Moreover, we extended its applicability in vivo, demonstrating that opto-PLCβ can enhance amygdala synaptic plasticity and associative fear learning in mice. Thus, opto-PLCβ offers precise spatiotemporal control, enabling comprehensive investigation of PLC-mediated signaling pathways, lipid dynamics, and their physiological consequences in vivo.

PKCδ is an activator of neuronal mitochondrial metabolism that mediates the spacing effect on memory consolidation

Relevance-based selectivity and high energy cost are two distinct features of long-term memory (LTM) formation that warrant its default inhibition. Spaced repetition of learning is a highly conserved cognitive mechanism that can lift this inhibition. Here, we questioned how the spacing effect integrates experience selection and energy efficiency at the cellular and molecular levels. We showed in Drosophila that spaced training triggers LTM formation by extending over several hours an increased mitochondrial metabolic activity in neurons of the associative memory center, the mushroom bodies (MBs). We found that this effect is mediated by PKCδ, a member of the so-called 'novel PKC' family of enzymes, which uncovers the critical function of PKCδ in neurons as a regulator of mitochondrial metabolism for LTM. Additionally, PKCδ activation and translocation to mitochondria result from LTM-specific dopamine signaling on MB neurons. By bridging experience-dependent neuronal circuit activity with metabolic modulation of memory-encoding neurons, PKCδ signaling binds the cognitive and metabolic constraints underlying LTM formation into a unified gating mechanism.

65 years of research on dopamine's role in classical fear conditioning and extinction: A systematic review

Dopamine, a catecholamine neurotransmitter, has historically been associated with the encoding of reward, whereas its role in aversion has received less attention. Here, we systematically gathered the vast evidence of the role of dopamine in the simplest forms of aversive learning: classical fear conditioning and extinction. In the past, crude methods were used to augment or inhibit dopamine to study its relationship with fear conditioning and extinction. More advanced techniques such as conditional genetic, chemogenic and optogenetic approaches now provide causal evidence for dopamine's role in these learning processes. Dopamine neurons encode conditioned stimuli during fear conditioning and extinction and convey the signal via activation of D1-4 receptor sites particularly in the amygdala, prefrontal cortex and striatum. The coordinated activation of dopamine receptors allows for the continuous formation, consolidation, retrieval and updating of fear and extinction memory in a dynamic and reciprocal manner. Based on the reviewed literature, we conclude that dopamine is crucial for the encoding of classical fear conditioning and extinction and contributes in a way that is comparable to its role in encoding reward.

MPP2 interacts with SK2 to rescue the excitability of glutamatergic neurons in the BLA and facilitate the extinction of conditioned fear in mice

AIMS

The basolateral amygdala (BLA) plays an integral role in anxiety disorders (such as post traumatic stress disorder) stem from dysregulated fear memory. The excitability of glutamatergic neurons in the BLA correlates with fear memory, and the afterhyperpolarization current (IAHP ) mediated by small-conductance calcium-activated potassium channel subtype 2 (SK2) dominates the excitability of glutamatergicneurons. This study aimed to explore the effect of MPP2 interacts with SK2 in the excitability of glutamatergic neurons in the BLA and the extinction of conditioned fear in mice.

METHODS

Fear memory was analyzed via freezing percentage. Western blotting and fluorescence quantitative PCR were used to determine the expression of protein and mRNA respectively. Electrophysiology was employed to measure the excitability of glutamatergic neurons and IAHP .

RESULTS

Fear conditioning decreased the levels of synaptic SK2 channels in the BLA, which were restored following fear extinction. Notably, reduced expression of synaptic SK2 channels in the BLA during fear conditioning was caused by the increased activity of protein kinase A (PKA), while increased levels of synaptic SK2 channels in the BLA during fear extinction were mediated by interactions with membrane-palmitoylated protein 2 (MPP2).

CONCLUSIONS

Our results revealed that MPP2 interacts with the SK2 channels and rescues the excitability of glutamatergic neurons by increasing the expression of synaptic SK2 channels in the BLA to promote the normalization of anxiety disorders and provide a new direction for the treatment.

Muscarinic antagonists impair multiple aspects of operant discrimination learning and performance

Acetylcholine signaling can strengthen associations between environmental cues and reward availability. Diverse subtypes (M1-M5) of the muscarinic acetylcholine receptor (mAChR) family may have distinct roles in different learning and memory processes, such as encoding cue-reward associations and consolidating these associations in long-term memory. Using an operant discrimination learning task in which mice are trained to nose poke during a tone to receive a food reward, we found that acquisition of the task requires mAChR signaling in the central nervous system. In addition, post-session injections of a broad mAChR antagonist, scopolamine impaired consolidation of the cue-reward memory. Further, after successful learning of a cue-reward contingency across multiple training sessions, mice that received a single pre-session injection of scopolamine were unable to use the learned cue association to receive rewards. Taken together, these data demonstrate distinct roles for muscarinic signaling in acquisition, consolidation and recall of the operant discrimination learning task. Understanding mechanisms underlying natural reward-related responding may provide insight into other maladaptive forms of reward learning such as addiction.

Dopaminergic and cholinergic modulation of the amygdala is altered in female mice with oestrogen receptor β deprivation

The amygdala is modulated by dopaminergic and cholinergic neurotransmission, and this modulation is altered in mood disorders. Therefore, this study was designed to evaluate the presence/absence of quantitative alterations in the expression of main dopaminergic and cholinergic markers in the amygdala of mice with oestrogen receptor β (ERβ) knock-out which exhibit increased anxiety, using immunohistochemistry and quantitative methods. Such alterations could either contribute to increased anxiety or be a compensatory mechanism for reducing anxiety. The results show that among dopaminergic markers, the expression of tyrosine hydroxylase (TH), dopamine transporter (DAT) and dopamine D₂-like receptor (DA₂) is significantly elevated in the amygdala of mice with ERβ deprivation when compared to matched controls, whereas the content of dopamine D₁-like receptor (DA₁) is not altered by ERβ knock-out. In the case of cholinergic markers, muscarinic acetylcholine type 1 receptor (AChR_M1) and alpha-7 nicotinic acetylcholine receptor (AChR_α7) display overexpression while the content of acetylcholinesterase (AChE) and vesicular acetylcholine transporter (VAChT) remains unchanged. In conclusion, in the amygdala of ERβ knock-out female the dopaminergic and cholinergic signalling is altered, however, to determine the exact role of ERβ in the anxiety-related behaviour further studies are required.

Effects of M currents on the persistent activity of pyramidal neurons in mouse primary auditory cortex

Neuronal persistent activity (PA) is a common phenomenon observed in many types of neurons. PA can be induced in neurons in the mouse auditory nucleus by activating cholinergic receptors with carbachol (CCh), a dual muscarinic and nicotinic receptor agonist. PA is presumed to be associated with learning-related auditory plasticity at the cellular level. However, the mechanism is not clearly understood. Many studies have reported that muscarinic cholinergic receptor agonists inhibit muscarinic-sensitive potassium channels (M channels). Potassium influx through M channels produces potassium currents, called M currents, which play an essential role in regulating neural excitability and synaptic plasticity. Further study is needed to determine whether M currents affect the PA of auditory central neurons and provide additional analysis of the variations in electrophysiological properties. We used in vitro whole-cell patch-clamp recordings in isolated mouse brain slices to investigate the effects of M currents on the PA in pyramidal neurons in layer V of the primary auditory cortex (AI-L5). We found that blocking M currents with XE991 depolarized the AI-L5 pyramidal neurons, which significantly increased the input resistance. The active threshold and threshold intensity were significantly reduced, indicating that the intrinsic excitability was enhanced. Our results also showed that blocking M currents with XE991 switched the neuronal firing patterns in the AI-L5 pyramidal neurons from regular-spiking to intrinsic-bursting. Blocking M currents facilitated PA by increasing the plateau potential and enhancing intrinsic excitability. Our results suggested that blocking M currents might facilitate the PA in AI-L5 pyramidal neurons, which underlies auditory plasticity.

Alternative Targets for Modulators of Mitochondrial Potassium Channels

Mitochondrial potassium channels control potassium influx into the mitochondrial matrix and thus regulate mitochondrial membrane potential, volume, respiration, and synthesis of reactive oxygen species (ROS). It has been found that pharmacological activation of mitochondrial potassium channels during ischemia/reperfusion (I/R) injury activates cytoprotective mechanisms resulting in increased cell survival. In cancer cells, the inhibition of these channels leads to increased cell death. Therefore, mitochondrial potassium channels are intriguing targets for the development of new pharmacological strategies. In most cases, however, the substances that modulate the mitochondrial potassium channels have a few alternative targets in the cell. This may result in unexpected or unwanted effects induced by these compounds. In our review, we briefly present the various classes of mitochondrial potassium (mitoK) channels and describe the chemical compounds that modulate their activity. We also describe examples of the multidirectional activity of the activators and inhibitors of mitochondrial potassium channels.

Neuropharmacology of Cevimeline and Muscarinic Drugs-Focus on Cognition and Neurodegeneration

At present, Alzheimer’s disease (AD) and related dementias cannot be cured. Therefore, scientists all over the world are trying to find a new approach to prolong an active life of patients with initial dementia. Both pharmacological and non-pharmacological pathways are investigated to improve the key symptom of the disease, memory loss. In this respect, influencing the neuromodulator acetylcholine via muscarinic receptors, such as cevimeline, might be one of the therapeutic alternatives. The purpose of this study is to explore the potential of cevimeline on the cognitive functions of AD patients. The methodology is based on a systematic literature review of available studies found in Web of Science, PubMed, Springer, and Scopus on the research topic. The findings indicate that cevimeline has shown an improvement in experimentally induced cognitive deficits in animal models. Furthermore, it has demonstrated to positively influence tau pathology and reduce the levels of amyloid-β (Aβ) peptide in the cerebral spinal fluid of Alzheimer’s patients. Although this drug has not been approved by the FDA for its use among AD patients and there is a lack of clinical studies confirming and extending this finding, cevimeline might represent a breakthrough in the treatment of AD.

Roles of PLCβ, PIP2 , and GIRK channels in arginine vasopressin-elicited excitation of CA1 pyramidal neurons

Arginine vasopressin (AVP) is a hormone exerting vasoconstrictive and antidiuretic action in the periphery and serves as a neuromodulator in the brain. Although the hippocampus receives vasopressinergic innervation and AVP has been shown to facilitate the excitability of CA1 pyramidal neurons, the involved ionic and signaling mechanisms have not been determined. Here we found that AVP excited CA1 pyramidal neurons by activation of V_1a receptors. Functions of G proteins and phospholipase Cβ (PLCβ) were required for AVP-elicited excitation of CA1 pyramidal neurons, whereas intracellular Ca²⁺ release and protein kinase C were unnecessary. PLCβ-mediated depletion of phosphatidylinositol 4,5-bisphosphate (PIP₂ ) was required for AVP-elicited excitation of CA1 pyramidal neurons. AVP augmented the input resistance and increased the time constants of CA1 pyramidal neurons. AVP induced an inward current in K⁺ -containing intracellular solution, whereas no inward currents were observed with Cs⁺ -containing intracellular solution. AVP-sensitive currents showed inward rectification with a reversal potential close to the K⁺ reversal potential, suggesting the involvement of inwardly rectifying K⁺ channels. AVP-induced currents were sensitive to the micromolar concentration of Ba²⁺ and tertiapin-Q, whereas application of ML 133, a selective Kir2 channel blocker had no effects, suggesting that AVP excited CA1 pyramidal neurons by depressing G protein-gated inwardly rectifying K⁺ channels. Activation of V_1a receptors in the CA1 region facilitated glutamatergic transmission onto subicular pyramidal neurons, suggesting that AVP modulates network activity in the brain. Our results may provide one of the cellular and molecular mechanisms to explain the in vivo physiological functions of AVP.

Neuromodulation of Persistent Activity and Working Memory Circuitry in Primate Prefrontal Cortex by Muscarinic Receptors

Neuromodulation by acetylcholine plays a vital role in shaping the physiology and functions of cerebral cortex. Cholinergic neuromodulation influences brain-state transitions, controls the gating of cortical sensory stimulus responses, and has been shown to influence the generation and maintenance of persistent activity in prefrontal cortex. Here we review our current understanding of the role of muscarinic cholinergic receptors in primate prefrontal cortex during its engagement in the performance of working memory tasks. We summarize the localization of muscarinic receptors in prefrontal cortex, review the effects of muscarinic neuromodulation on arousal, working memory and cognitive control tasks, and describe the effects of muscarinic M1 receptor stimulation and blockade on the generation and maintenance of persistent activity of prefrontal neurons encoding working memory representations. Recent studies describing the pharmacological effects of M1 receptors on prefrontal persistent activity demonstrate the heterogeneity of muscarinic actions and delineate unexpected modulatory effects discovered in primate prefrontal cortex when compared with studies in rodents. Understanding the underlying mechanisms by which muscarinic receptors regulate prefrontal cognitive control circuitry will inform the search of muscarinic-based therapeutic targets in the treatment of neuropsychiatric disorders.

Beneficial effect of retigabine on memory in rats receiving ethanol

Background

Retigabine belongs to the novel generation of antiepileptic drugs but its complex mechanism of action causes that the drug might be effective in other diseases, for instance, alcohol dependence. It is known that ethanol abuse impaired the function of brain structures associated with memory and learning such as the hippocampus. In our previous study, retigabine reduced hippocampal changes induced by ethanol in the EEG rhythms in rabbits. This study is focused on the impact of retigabine on memory processes in male rats receiving alcohol.

Methods

Memory was evaluated in various experimental models: Morris water maze, Contextual, and Cued Fear Conditioning tests. Retigabine was administered for 3 weeks directly to the stomach via oral gavage at a dose of 10 mg/kg. Rats received also 20% ethanol (5 g/kg/day in two doses) via oral gavage for 3 weeks and had free access to 5% ethanol in the afternoon and at night. Morris water maze was performed after 1 and 3 weeks of ethanol administration and after 1 week from the discontinuation of ethanol administration. Contextual and Cued Fear Conditioning tests were carried out after 24 h and 72 h of alcohol discontinuation.

Results

The drug significantly decreased ethanol-induced memory disturbances during alcohol administration as well as slightly improved learning processes after the discontinuation of ethanol administration.

Conclusions

This beneficial effect of retigabine-ethanol interaction on memory may be a relevant element of the drug’s impact on the development of addiction.

Kv7 Channels and Excitability Disorders

Kv7.1-Kv7.5 (KCNQ1-5) K⁺ channels are voltage-gated K⁺ channels with major roles in neurons, muscle cells and epithelia where they underlie physiologically important K⁺ currents, such as neuronal M current and cardiac I_Ks. Specific biophysical properties of Kv7 channels make them particularly well placed to control the activity of excitable cells. Indeed, these channels often work as 'excitability breaks' and are targeted by various hormones and modulators to regulate cellular activity outputs. Genetic deficiencies in all five KCNQ genes result in human excitability disorders, including epilepsy, arrhythmias, deafness and some others. Not surprisingly, this channel family attracts considerable attention as potential drug targets. Here we will review biophysical properties and tissue expression profile of Kv7 channels, discuss recent advances in the understanding of their structure as well as their role in various neurological, cardiovascular and other diseases and pathologies. We will also consider a scope for therapeutic targeting of Kv7 channels for treatment of the above health conditions.

Eleutheroside E Enhances the Long-Term Memory of Radiation-Damaged C. elegans through G-Protein-Coupled Receptor and Neuropeptide Signaling Pathways

Eleutheroside E (EE), a principal active compound of Acanthopanax senticosus, has been shown to have a certain neuromodulation effect. Our previous study indicates that EE protects nerve damage caused by radiation. However, its specific function and underlying mechanism remain unknown. Therefore, the objective of this study is to apply the C. elegans model to illuminate the property and mechanism of EE protecting against nerve damage caused by radiation. Here, we found that EE significantly improved the long-term memory of radiation-damaged C. elegans. Through transcriptome sequencing, the results showed that EE protected radiation-damaged C. elegans mainly through G-protein-coupled receptor and neuropeptide signaling pathways. Further research indicated that EE affected the activity of CREB by cAMP-PKA, G_qα-PLC, and neuropeptide signaling pathways to ultimately improve the long-term memory of radiation-damaged C. elegans. In addition, the activity of G_qα and neuropeptides in AWC neurons and the activity of CREB in AIM neurons might be crucial for EE to function.

Beneficial role of central anticholinergic agent in preventing the development of symptoms in mouse model of post-traumatic stress disorder

Objectives The present study was designed to investigate the effectiveness of trihexyphenidyl, a central anticholinergic drug, in preventing the post-traumatic stress disorder (PTSD) symptoms in a mouse model. Methods Mice were subjected to underwater trauma stress for 30 s on day 1 followed by three situational reminders (3rd, 7th and 14th day). Thereafter, the behavioral alterations including freezing behavior were noted on 21st day. The serum corticosterone levels were measured as a biochemical marker of trauma. Elevated plus maze test was done on day 1 and day 2 to assess the memory formation following exposure to trauma. Results Trauma and situational reminders were associated with a significant development of behavioral changes and freezing behavior on the 21st day. Moreover, there was also a significant decrease in the serum corticosterone levels. A single administration of trihexyphenidyl (2 and 5 mg/kg) significantly restored trauma associated-behavioral changes and serum corticosterone levels. Moreover, it significantly increased the transfer latency time on day 2 following stress exposure in comparison to normal mice suggesting the inhibition of memory formation during trauma exposure. Trihexyphenidyl also led to significant reduction in freezing behavior in response to situational reminders again suggesting the inhibition of formation of aversive fear memory. Conclusion The blockade of central muscarinic receptors may block the formation of aversive memory during the traumatic event, which may be manifested in form of decreased contextual fear response during situational reminders. Central anticholinergic agents may be potentially useful as prophylactic agents in preventing the development of PTSD symptoms.

Ih, GIRK, and KCNQ/Kv7 channels differently modulate sharp wave - ripples in the dorsal and ventral hippocampus

Sharp waves and ripples (SPW-Rs) are endogenous transient patterns of hippocampus local network activity implicated in several functions including memory consolidation, and they are diversified between the dorsal and the ventral hippocampus. Ion channels in the neuronal membrane play important roles in cell and local network function. In this study, using transverse slices and field potential recordings from the CA1 field of rat hippocampus we show that GIRK and KCNQ2/3 potassium channels play a higher role in modulating SPW-Rs in the dorsal hippocampus, while I_h and other KCNQ (presumably KCNQ5) channels, contribute to shaping SPW-R activity more in the ventral than in dorsal hippocampus. Specifically, blockade of I_h channels by ZD 7288 reduced the rate of occurrence of SPW-Rs and increased the generation of SPW-Rs in the form of clusters in both hippocampal segments, while enhanced the amplitude of SPW-Rs only in the ventral hippocampus. Most effects of ZD 7288 appeared to be independent of NMDA receptors' activity. However, the effects of blockade of NMDA receptors depended on the functional state of I_h channels in both hippocampal segments. Blockade of GIRK channels by Tertiapin-Q increased the rate of occurrence of SPW-Rs only in the dorsal hippocampus and the probability of clusters in both segments of the hippocampus. Blockade of KCNQ2/3 channels by XE 991 increased the rate of occurrence of SPW-Rs and the probability of clusters in the dorsal hippocampus, and only reduced the clustered generation of SPW-Rs in the ventral hippocampus. The blocker of KCNQ1/2 channels, that also enhances KCNQ5 channels, UCL 2077, increased the probability of clusters and the power of the ripple oscillation in the ventral hippocampus only. These results suggest that GIRK, KCNQ and I_h channels represent a key mechanism for modulation of SPW-R activity which act differently in the dorsal and ventral hippocampus, fundamentally supporting functional diversification along the dorsal-ventral axis of the hippocampus.

Inhibition of M/Kv7 Currents Contributes to Chloroquine-Induced Itch in Mice

M/K_v7 potassium channels play a key role in regulation of neuronal excitability. Modulation of neuronal excitability of primary sensory neurons determines the itch sensation induced by a variety of itch-causing substances including chloroquine (CQ). In the present study, we demonstrate that suppression of M/K_v7 channel activity contributes to generation of itch in mice. CQ enhances excitability of the primary sensory neurons through inhibiting M/K_v7 potassium currents in a Ca²⁺ influx-dependent manner. Specific M/K_v7 channel opener retigabine (RTG) or tannic acid (TA) not only reverses the CQ-induced enhancement of neuronal excitability but also suppresses the CQ-induced itch behavior. Systemic application of RTG or TA also significantly inhibits the itch behavior induced by a variety of pruritogens. Taken together, our findings provide novel insight into the molecular basis of CQ-induced itch sensation in mammals that can be applied to the development of strategies to mitigate itch behavior.

Hippocampal knockdown of α2 nicotinic or M1 muscarinic acetylcholine receptors in C57BL/6J male mice impairs cued fear conditioning

Acetylcholine (ACh) signaling in the hippocampus is important for behaviors related to learning, memory and stress. In this study, we investigated the role of two ACh receptor subtypes previously shown to be involved in fear and anxiety, the M1 mAChR and the α2 nAChR, in mediating the effects of hippocampal ACh on stress-related behaviors. Adeno-associated viral vectors containing short-hairpin RNAs targeting M1 or α2 were infused into the hippocampus of male C57BL/6J mice, and behavior in a number of paradigms related to stress responses and fear learning was evaluated. There were no robust effects of hippocampal M1 mAChR or α2 nAChR knockdown (KD) in the light/dark box, tail suspension, forced swim or novelty-suppressed feeding tests. However, effects on fear learning were observed in both KD groups. Short term learning was intact immediately after training in all groups of mice, but both the M1 and α2 hippocampal knock down resulted in impaired cued fear conditioning 24 h after training. In addition, there was a trend for a deficit in contextual memory the M1 mAChR KD group 24 h after training. These results suggest that α2 nicotinic and M1 muscarinic ACh receptors in the hippocampus contribute to fear learning and could be relevant targets to modify brain circuits involved in stress-induced reactivity to associated cues.

Metabotropic Modulation of Potassium Channels During Synaptic Plasticity

Besides their primary function mediating the repolarization phase of action potentials, potassium channels exquisitely and ubiquitously regulate the resting membrane potential of neurons and therefore have a key role establishing their intrinsic excitability. This group of proteins is composed of a very diverse collection of voltage-dependent and -independent ion channels, whose specific distribution is finely tuned at the level of the synapse. Both at the presynaptic and postsynaptic membranes, different types of potassium channels are subjected to modulation by second messenger signaling cascades triggered by metabotropic receptors, which in this way serve as a link between neurotransmitter actions and changes in the neuron membrane excitability. On the one hand, by regulating the resting membrane potential of the postsynaptic membrane, potassium channels appear to be critical towards setting the threshold for the induction of long-term potentiation and depression. On the other hand, these channels maintain the presynaptic membrane potential under control, therefore influencing the probability of neurotransmitter release underlying different forms of short-term plasticity. In the present review, we examine in detail the role of metabotropic receptors translating their activation by different neurotransmitters into a final effect modulating several types of potassium channels. Furthermore, we evaluate the consequences that this interplay has on the induction and maintenance of different forms of synaptic plasticity.

M1 Muscarinic Receptors Modulate Fear-Related Inputs to the Prefrontal Cortex: Implications for Novel Treatments of Posttraumatic Stress Disorder

BACKGROUND

The prefrontal cortex (PFC) integrates information from multiple inputs to exert top-down control allowing for appropriate responses in a given context. In psychiatric disorders such as posttraumatic stress disorder, PFC hyperactivity is associated with inappropriate fear in safe situations. We previously reported a form of muscarinic acetylcholine receptor (mAChR)-dependent long-term depression in the PFC that we hypothesize is involved in appropriate fear responding and could serve to reduce cortical hyperactivity following stress. However, it is unknown whether this long-term depression occurs at fear-related inputs.

METHODS

Using optogenetics with extracellular and whole-cell electrophysiology, we assessed the effect of mAChR activation on the synaptic strength of specific PFC inputs. We used selective pharmacological tools to assess the involvement of M1 mAChRs in conditioned fear extinction in control mice and in the stress-enhanced fear-learning model.

RESULTS

M1 mAChR activation induced long-term depression at inputs from the ventral hippocampus and basolateral amygdala but not from the mediodorsal nucleus of the thalamus. We found that systemic M1 mAChR antagonism impaired contextual fear extinction. Treatment with an M1 positive allosteric modulator enhanced contextual fear extinction consolidation in stress-enhanced fear learning-conditioned mice.

CONCLUSIONS

M1 mAChRs dynamically modulate synaptic transmission at two PFC inputs whose activity is necessary for fear extinction, and M1 mAChR function is required for proper contextual fear extinction. Furthermore, an M1 positive allosteric modulator enhanced the consolidation of fear extinction in the stress-enhanced fear-learning model, suggesting that M1 positive allosteric modulators may provide a novel treatment strategy to facilitate exposure therapy in the clinic for the treatment of posttraumatic stress disorder.

Role of Thioredoxin 1 in Impaired Renal Sodium Excretion of hD 5 R F173L Transgenic Mice

Background Dopamine D5 receptor (D5R) plays an important role in the maintenance of blood pressure by regulating renal sodium transport. Our previous study found that human D5R mutant F173L transgenic ( hD 5 R F173L-TG) mice are hypertensive. In the present study, we aimed to investigate the mechanisms causing this renal D5R dysfunction in hD 5 R F173L-TG mice. Methods and Results Compared with wild-type D5R-TG ( hD 5 R WT-TG) mice, hD 5 R F173L-TG mice have higher blood pressure, lower basal urine flow and sodium excretion, and impaired agonist-mediated natriuresis and diuresis. Enhanced reactive oxygen species production in hD 5 R F173L-TG mice is caused, in part, by decreased expression of antioxidant enzymes, including thioredoxin 1 (Trx1). Na+-K+-ATPase activity is increased in mouse renal proximal tubule cells transfected with hD 5 R F173L, but is normalized by treatment with exogenous recombinant human Trx1 protein. Regulation of Trx1 by D5R occurs by the phospholipase C/ protein kinase C (PKC) pathway because upregulation of Trx1 expression by D5R does not occur in renal proximal tubule cells from D1R knockout mice in the presence of a phospholipase C or PKC inhibitor. Fenoldopam, a D1R and D5R agonist, stimulates PKC activity in primary renal proximal tubule cells of hD5R WT -TG mice, but not in those of hD 5 R F173L-TG mice. Hyperphosphorylation of hD5RF173L and its dissociation from Gαs and Gαq are associated with impairment of D5R-mediated inhibition of Na+-K+-ATPase activity in hD 5 R F173L-TG mice. Conclusions These suggest that hD 5 R F173L increases blood pressure, in part, by decreasing renal Trx1 expression and increasing reactive oxygen species production. Hyperphosphorylation of hD5RF173L, with its dissociation from Gαs and Gαq, is the key factor in impaired D5R function of hD 5 R F173L-TG mice.

Norepinephrine Induces PTSD-Like Memory Impairments via Regulation of the β-Adrenoceptor-cAMP/PKA and CaMK II/PKC Systems in the Basolateral Amygdala

Glucocorticoids (GCs) can modulate the memory enhancement process during stressful events, and this modulation requires arousal-induced norepinephrine (NE) activation in the basolateral amygdale (BLA). Our previous study found that an intrahippocampal infusion of propranolol dose-dependently induced post-traumatic stress disorder (PTSD)-like memory impairments. To explore the role of the noradrenergic system of the BLA in PTSD-like memory impairment, we injected various doses of NE into the BLA. We found that only a specific quantity of NE (0.3 μg) could induce PTSD-like memory impairments, accompanied by a reduction in phosphorylation of GluR1 at Ser845 and Ser831. Moreover, this phenomenon could be blocked by a protein kinase A (PKA) inhibitor or calcium/calmodulin-dependent protein kinase II (CaMK II) inhibitor. These findings demonstrate that NE could induce PTSD-like memory impairments via regulation of the β-adrenoceptor receptor (β-AR)-3′,5′-cyclic monophosphate (cAMP)/PKA and CaMK II/PKC signaling pathways.

Preclinical to Human Translational Pharmacology of the Novel M1 Positive Allosteric Modulator MK-7622

The current standard of care for treating Alzheimer's disease is acetylcholinesterase inhibitors, which nonselectively increase cholinergic signaling by indirectly enhancing activity of nicotinic and muscarinic receptors. These drugs improve cognitive function in patients, but also produce unwanted side effects that limit their efficacy. In an effort to selectively improve cognition and avoid the cholinergic side effects associated with the standard of care, various efforts have been aimed at developing selective M1 muscarinic receptor activators. In this work, we describe the preclinical and clinical pharmacodynamic effects of the M1 muscarinic receptor-positive allosteric modulator, MK-7622. MK-7622 attenuated the cognitive-impairing effects of the muscarinic receptor antagonist scopolamine and altered quantitative electroencephalography (qEEG) in both rhesus macaque and human. For both scopolamine reversal and qEEG, the effective exposures were similar between species. However, across species the minimum effective exposures to attenuate the scopolamine impairment were lower than for qEEG. Additionally, there were differences in the spectral power changes produced by MK-7622 in rhesus versus human. In sum, these results are the first to demonstrate translation of preclinical cognition and target modulation to clinical effects in humans for a selective M1 muscarinic receptor-positive allosteric modulator.

Muscarinic receptor subtype distribution in the central nervous system and relevance to aging and Alzheimer's disease

Muscarinic acetylcholine receptors (mAChRs) are G proteincoupled receptors (GPCRs) that mediate the metabotropic actions of acetylcholine (ACh). There are five subtypes of mAChR, M₁ - M₅, which are expressed throughout the central nervous system (CNS) on numerous cell types and represent promising treatment targets for a number of different diseases, disorders, and conditions of the CNS. Although the present review will focus on Alzheimer's disease (AD) and amnestic mild cognitive impairment (aMCI), a number of conditions such as Parkinson's disease (PD), schizophrenia, and others represent significant unmet medical needs for which selective muscarinic agents could offer therapeutic benefits. Numerous advances have been made regarding mAChR localization through the use of subtype-selective antibodies and radioligand binding studies and these efforts have helped propel a number of mAChR therapeutics into clinical trials. However, much of what we know about mAChR localization in the healthy and diseased brain has come from studies employing radioligand binding with relatively modest selectivity. The development of subtype-selective small molecule radioligands suitable for in vitro and in vivo use, as well as robust, commercially-available antibodies remains a critical need for the field. Additionally, novel genetic tools should be developed and leveraged to help move the field increasingly towards a systems-level understanding of mAChR subtype action. Finally, functional, proteomic, and genetic data from ongoing human studies hold great promise for optimizing the design and interpretation of studies examining receptor levels by enabling patient stratification. This article is part of the Special Issue entitled 'Neuropharmacology on Muscarinic Receptors'.

Effects of calcium-dependent molecular chaperones and endoplasmic reticulum in the amygdala in rats under single‑prolonged stress

The purpose of the present study was to investigate the role of endoplasmic reticulum (ER)‑resident molecular chaperone proteins to identify whether these proteins were involved in post‑traumatic stress disorder (PTSD). The present study detected changes of calreticulin (CRT), calnexin (CNX) and ERp57 in the amygdala of rats, which may with aim of providing a novel insight into the modulation effect of amygdala in PTSD. Single‑prolonged stress (SPS) was applied to create the models of PTSD in rats. The expression levels of CRT, CNX and ERp57 were examined using immunohistochemistry or immunofluorescence, western blot analysis and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). The results showed that SPS induced significant changes in CRT, CNX and ERp57 expression levels. Furthermore, the expression levels of CRT, CNX and ERp57 were significantly upregulated when compared to that in the control group after SPS exposure by western blot analysis (P<0.05). RT‑qPCR analysis supported these results, indicating an upregulation of mRNA expression level. Taken together, the present findings suggest that SPS may induce changes to the expression of CRT, CNX and ERp57 in the amygdala of rats. The present study provides an insight into the effects of ER‑resident molecular chaperones in the amygdala participating in PTSD, and provides the experimental basis and a mechanism for the pathophysiology of PTSD.

Physiological roles of CNS muscarinic receptors gained from knockout mice

Because the five muscarinic acetylcholine receptor subtypes have overlapping distributions in many CNS tissues, and because ligands with a high degree of selectivity for a given subtype long remained elusive, it has been difficult to determine the physiological functions of each receptor. Genetically engineered knockout mice, in which one or more muscarinic acetylcholine receptor subtype has been inactivated, have been instrumental in identifying muscarinic receptor functions in the CNS, at the neuronal, circuit, and behavioral level. These studies revealed important functions of muscarinic receptors modulating neuronal activity and neurotransmitter release in many brain regions, shaping neuronal plasticity, and affecting functions ranging from motor and sensory function to cognitive processes. As gene targeting technology evolves including the use of conditional, cell type specific strains, knockout mice are likely to continue to provide valuable insights into brain physiology and pathophysiology, and advance the development of new medications for a range of conditions such as Alzheimer's disease, Parkinson's disease, schizophrenia, and addictions, as well as non-opioid analgesics. This article is part of the Special Issue entitled 'Neuropharmacology on Muscarinic Receptors'.

XE991 and Linopirdine Are State-Dependent Inhibitors for Kv7/KCNQ Channels that Favor Activated Single Subunits

M-channel inhibitors, especially XE991, are being used increasingly in animal experiments; however, insufficient characterization of XE991 at times confounds the interpretation of results when using this compound. Here, we demonstrate that XE991 and linopirdine are state-dependent inhibitors that favor the activated-subunit of neuronal Kv7/KCNQ channels. We performed patch-clamp experiments on homomeric Kv7.2 or heteromeric Kv7.2/3 channels expressed in Chinese hamster ovary cells to characterize XE991 and linopirdine. Neither inhibitor was efficacious around the resting membrane potential of cells in physiologic conditions. Inhibition of Kv7.2 and Kv7.2/3 channels by XE991 was closely related with channel activation. When the voltage dependence of activation was left-shifted by retigabine or right-shifted by the mutation, Kv7.2(R214D), the shift in half-activation voltage proportionally coincided with the shift in the half-effective potential for XE991 inhibition. Inhibition kinetics during XE991 wash-in was facilitated at depolarized potentials. Ten-minute washout of XE991 resulted in ∼30% current recovery, most of which was attributed to surface transport of Kv7.2 channels. Linopirdine also exhibited similar inhibition characteristics, with the exception of near- complete current recovery after washout at depolarized potentials. Inhibition kinetics of both XE991 and linopirdine was not as sensitive to changes in voltage as would be predicted by open- channel inhibition. Instead, they were well explained by binding to a single activated subunit. The characteristics of XE991 and linopirdine should be taken into account when these M-channel inhibitors are used in experiments.

M1 muscarinic receptors are necessary for retrieval of remote context fear memory

Several studies have investigated the transition of consolidation of recent memory to remote memory in aversively motivated tasks, such as contextual fear conditioning (CFC) and inhibitory avoidance (IA). However, the mechanisms that serve the retrieval of remote memories, has not yet been fully understood. Some evidences suggest that the central cholinergic system appears be involved in the modulation of these processes. Therefore, the present study aimed to investigate the effects of a pre-test administration of dicyclomine, a high-affinity M1 muscarinic receptor antagonist, on the retrieval of remote memories in fear conditioning and IA tasks. Male Wistar rats were trained, and after 1 or 28days, the rats received dicyclomine (16 or 32mg/kg, intraperitoneally, i.p.) and were tested in CFC, tone fear conditioning (TFC) and IA tasks. At both time intervals, 32mg/kg dicyclomine induced impairment of CFC. In TFC task only the performance of the rats 28days after training was impaired. The IA task was not affected in any of the studied intervals. These findings suggest a differential contribution of muscarinic receptors on recent and remote memories retrieval revealing a more generalized role in remote memory.

Muscarinic acetylcholine receptors act in synergy to facilitate learning and memory

Understanding how episodic memories are formed and retrieved is necessary if we are to treat disorders in which they malfunction. Muscarinic acetylcholine receptors (mAChR) in the hippocampus and cortex underlie memory formation, but there is conflicting evidence regarding their role in memory retrieval. Additionally, there is no consensus on which mAChR subtypes are critical for memory processing. Using pharmacological and genetic approaches, we found that (1) encoding and retrieval of contextual memory requires mAChR in the dorsal hippocampus (DH) and retrosplenial cortex (RSC), (2) memory formation requires hippocampal M₃ and cooperative activity of RSC M₁ and M_3, and (3) memory retrieval is more impaired by inactivation of multiple M₁–M₄ mAChR in DH or RSC than inactivation of individual receptor subtypes. Contrary to the view that acetylcholine supports learning but is detrimental to memory retrieval, we found that coactivation of multiple mAChR is required for retrieval of both recently and remotely acquired context memories. Manipulations with higher receptor specificity were generally less potent than manipulations targeting multiple receptor subtypes, suggesting that mAChR act in synergy to regulate memory processes. These findings provide unique insight into the development of therapies for amnestic symptoms, suggesting that broadly acting, rather than receptor-specific, mAchR agonists and positive allosteric modulators may be the most effective therapeutic approach.

Cholinergic regulation of fear learning and extinction

Cholinergic activation regulates cognitive function, particularly long-term memory consolidation. This Review presents an overview of the anatomical, neurochemical, and pharmacological evidence supporting the cholinergic regulation of Pavlovian contextual and cue-conditioned fear learning and extinction. Basal forebrain cholinergic neurons provide inputs to neocortical regions and subcortical limbic structures such as the hippocampus and amygdala. Pharmacological manipulations of muscarinic and nicotinic receptors support the role of cholinergic processes in the amygdala, hippocampus, and prefrontal cortex in modulating the learning and extinction of contexts or cues associated with threat. Additional evidence from lesion studies and analysis of in vivo acetylcholine release with microdialysis similarly support a critical role of cholinergic neurotransmission in corticoamygdalar or corticohippocampal circuits during acquisition of fear extinction. Although a few studies have suggested a complex role of cholinergic neurotransmission in the cellular plasticity essential for extinction learning, more work is required to elucidate the exact cholinergic mechanisms and physiological role of muscarinic and nicotinic receptors in these fear circuits. Such studies are important for elucidating the role of cholinergic neurotransmission in disorders such as posttraumatic stress disorder that involve deficits in extinction learning as well as for developing novel therapeutic approaches for such disorders. © 2016 Wiley Periodicals, Inc.

RGS2 expression predicts amyloid-β sensitivity, MCI and Alzheimer's disease: genome-wide transcriptomic profiling and bioinformatics data mining

Alzheimer's disease (AD) is the most frequent cause of dementia. Misfolded protein pathological hallmarks of AD are brain deposits of amyloid-β (Aβ) plaques and phosphorylated tau neurofibrillary tangles. However, doubts about the role of Aβ in AD pathology have been raised as Aβ is a common component of extracellular brain deposits found, also by in vivo imaging, in non-demented aged individuals. It has been suggested that some individuals are more prone to Aβ neurotoxicity and hence more likely to develop AD when aging brains start accumulating Aβ plaques. Here, we applied genome-wide transcriptomic profiling of lymphoblastoid cells lines (LCLs) from healthy individuals and AD patients for identifying genes that predict sensitivity to Aβ. Real-time PCR validation identified 3.78-fold lower expression of RGS2 (regulator of G-protein signaling 2; P=0.0085) in LCLs from healthy individuals exhibiting high vs low Aβ sensitivity. Furthermore, RGS2 showed 3.3-fold lower expression (P=0.0008) in AD LCLs compared with controls. Notably, RGS2 expression in AD LCLs correlated with the patients' cognitive function. Lower RGS2 expression levels were also discovered in published expression data sets from postmortem AD brain tissues as well as in mild cognitive impairment and AD blood samples compared with controls. In conclusion, Aβ sensitivity phenotyping followed by transcriptomic profiling and published patient data mining identified reduced peripheral and brain expression levels of RGS2, a key regulator of G-protein-coupled receptor signaling and neuronal plasticity. RGS2 is suggested as a novel AD biomarker (alongside other genes) toward early AD detection and future disease modifying therapeutics.

Modulation of Kv7 channels and excitability in the brain

Neuronal Kv7 channels underlie a voltage-gated non-inactivating potassium current known as the M-current. Due to its particular characteristics, Kv7 channels show pronounced control over the excitability of neurons. We will discuss various factors that have been shown to drastically alter the activity of this channel such as protein and phospholipid interactions, phosphorylation, calcium, and numerous neurotransmitters. Kv7 channels locate to key areas for the control of action potential initiation and propagation. Moreover, we will explore the dynamic surface expression of the channel modulated by neurotransmitters and neural activity. We will also focus on known principle functions of neural Kv7 channels: control of resting membrane potential and spiking threshold, setting the firing frequency, afterhyperpolarization after burst firing, theta resonance, and transient hyperexcitability from neurotransmitter-induced suppression of the M-current. Finally, we will discuss the contribution of altered Kv7 activity to pathologies such as epilepsy and cognitive deficits.

Neuromodulatory signaling in hippocampus-dependent memory retrieval

Considerable advances have been made toward understanding the molecular signaling events that underlie memory acquisition and consolidation. In contrast, less is known about memory retrieval, despite its necessity for utilizing learned information. This review focuses on neuromodulatory and intracellular signaling events that underlie memory retrieval mediated by the hippocampus, for which the most information is currently available. Among neuromodulators, adrenergic signaling is required for the retrieval of various types of hippocampus-dependent memory. Although they contribute to acquisition and/or consolidation, cholinergic and dopaminergic signaling are generally not required for retrieval. Interestingly, while not required for retrieval, serotonergic and opioid signaling may actually constrain memory retrieval. Roles for histamine and non-opioid neuropeptides are currently unclear but possible. A critical effector of adrenergic signaling in retrieval is reduction of the slow afterhyperpolarization mediated by β1 receptors, cyclic AMP, protein kinase A, Epac, and possibly ERK. In contrast, stress and glucocorticoids impair retrieval by decreasing cyclic AMP, mediated in part by the activation of β2 -adrenergic receptors. Clinically, alterations in neuromodulatory signaling and in memory retrieval occur in Alzheimer's disease, Down syndrome, depression, and post-traumatic stress disorder, and recent evidence has begun to link changes in neuromodulatory signaling with effects on memory retrieval.