Memantine Blocks α7* Nicotinic Acetylcholine Receptors More Potently Than N-Methyl-D-aspartate Receptors in Rat Hippocampal Neurons

Cellular Mechanisms of Cognitive Enhancement: The In Vivo Modulation of the Firing Activity and the Responsiveness of Rat Hippocampal Neurons by Memantine and Alpha7 Nicotinic Acetylcholine Receptor Ligands

Promising new pharmacological strategies for the enhancement of cognition target either nicotinic acetylcholine receptors (nAChR) or N-methyl-D-aspartate receptors (NMDAR). There is also an increasing interest in low-dose combination therapies co-targeting the above neurotransmitter systems to reach greater efficacy over the monotreatments and to reduce possible side effects of high-dose monotreatments. In the present study, we assessed modulatory effects of the α7 nAChR-selective agonist PHA-543613 (PHA), a novel α7 nAChR positive allosteric modulator compound (CompoundX) and the NMDAR antagonist memantine on the in vivo firing activity of CA1 pyramidal neurons in the rat hippocampus. Three different test conditions were applied: spontaneous firing activity, NMDA-evoked firing activity and ACh-evoked firing activity. Results showed that high but not low doses of memantine decreased NMDA-evoked firing activity, and low doses increased the spontaneous and ACh-evoked firing activity. Systemically applied PHA robustly potentiated ACh-evoked firing activity with having no effect on NMDA-evoked activity. In addition, CompoundX increased both NMDA- and ACh-evoked firing activity, having no effects on spontaneous firing of the neurons. A combination of low doses of memantine and PHA increased firing activity in all test conditions and similar effects were observed with memantine and CompoundX but without spontaneous firing activity increasing effects. Our present results demonstrate that α7 nAChR agents beneficially interact with Alzheimer's disease medication memantine. Moreover, positive allosteric modulators potentiate memantine effects on the right time and the right place without affecting spontaneous firing activity. All these data confirm previous behavioral evidence for the viability of combination therapies for cognitive enhancement.

Memantine: Updating a rare success story in pro-cognitive therapeutics

The great potential for NMDA receptor modulators as druggable targets in neurodegenerative disorders has been met with limited success. Considered one of the rare exceptions, memantine has consistently demonstrated restorative and prophylactic properties in many AD models. In clinical trials memantine slows the decline in cognitive performance associated with AD. Here, we provide an overview of the basic properties including pharmacological targets, toxicology and cellular effects of memantine. Evidence demonstrating reductions in molecular, physiological and behavioural indices of AD-like impairments associated with memantine treatment are also discussed. This represents both an extension and homage to Dr. Chris Parson's considerable contributions to our fundamental understanding of a success story in the AD treatment landscape.

Targeting synapse function and loss for treatment of neurodegenerative diseases

Synapse dysfunction and loss are hallmarks of neurodegenerative diseases that correlate with cognitive decline. However, the mechanisms and therapeutic strategies to prevent or reverse synaptic damage remain elusive. In this Review, we discuss recent advances in understanding the molecular and cellular pathways that impair synapses in neurodegenerative diseases, including the effects of protein aggregation and neuroinflammation. We also highlight emerging therapeutic approaches that aim to restore synaptic function and integrity, such as enhancing synaptic plasticity, preventing synaptotoxicity, modulating neuronal network activity and targeting immune signalling. We discuss the preclinical and clinical evidence for each strategy, as well as the challenges and opportunities for developing effective synapse-targeting therapeutics for neurodegenerative diseases.

Acute and chronic glutamate NMDA antagonist treatment attenuates dopamine D1 antagonist-induced reduction of nicotine self-administration in female rats

Multiple interacting neural systems are involved in sustaining nicotine reinforcement. We and others have shown that dopamine D1 receptors and glutamate NMDA receptors both play important roles in nicotine reinforcement. Blockade of D1 receptors with the antagonist SCH-23390 (0.02 mg/kg) both acutely and chronically significantly decreased nicotine self-administration in rats. Blockade of NMDA receptors (10 mg/kg) acutely with memantine significantly increased nicotine self-administration, but chronic blockade of NMDA receptors with memantine significantly decreased nicotine self-administration. The current study examined the interactions of acute and chronic administration of SCH-23390 and memantine on nicotine self-administration in female rats. Replicating earlier studies, acute and chronic SCH-23390 significantly decreased nicotine self-administration and memantine had a biphasic effect with acute administration increasing nicotine self-administration and chronic memantine showed a non-significant trend toward decreasing it. However, chronic interaction study showed that memantine significantly attenuated the decrease in nicotine self-administration caused by chronic SCH-23390. These studies provide important information that memantine attenuates the efficacy of D1 antagonist SCH 23390 in reducing nicotine-self-administration. These two drugs do not appear to have mutually potentiating effects to aid tobacco cessation.

Nicotinic acetylcholine receptors in cancer: Limitations and prospects

Nicotinic acetylcholine receptors (nAChRs) have long been considered to solely mediate neurotransmission. However, their widespread distribution in the human body suggests a more diverse physiological role. Additionally, the expression of nAChRs is increased in certain cancers, such as lung cancer, and has been associated with cell proliferation, epithelial-to-mesenchymal cell transition, angiogenesis and apoptosis prevention. Several compounds that interact with these receptors have been identified as potential therapeutic agents. They have been tested as drugs for treating nicotine addiction, alcoholism, depression, pain and Alzheimer's disease. This review focuses on nAChR-mediated signalling in cancer, presenting opportunities for the development of innovative nAChR-based anticancer drugs. It displays the differences in expression of each nAChR subunit between normal and cancer cells for selected cancer types, highlighting their possible involvement in specific cases. Antagonists of nAChRs that could complement existing cancer therapies are summarised and critically discussed. We hope that this review will stimulate further research on the role of nAChRs in cancer potentially leading to innovative cancer therapies.

The Role of NMDA Receptor Subunits in the Effect of Memantine on the Brain of Healthy Animals

The non-competitive NMDA glutamate receptor antagonist memantine has neuroprotective properties and is the first non-cholinergic drug approved for the treatment of Alzheimer's disease. The purpose of this work was to test the hypothesis that injections of memantine to healthy animals can affect the subunit composition of NMDA receptors in the brain, which may explain the effects of its chronic administration. For this, the expression of subunits GluN1, GluN2A, GluN2B, and GluN2C was studied in the hippocampus and prefrontal cortex of rats after single or five subchronic injections of memantine. The results showed that the GluN2C subunit (GRIN2C) plays an important role in the effects of memantine; against the background of memantine treatment, the expression of this subunit markedly decreased in the prefrontal cortex, but not in the hippocampus, which significantly affected the excitation/inhibition balance in cortical structures.

The Disruption of NMDAR/TRPM4 Death Signaling with TwinF Interface Inhibitors: A New Pharmacological Principle for Neuroprotection

With the discovery that the acquisition of toxic features by extrasynaptic NMDA receptors (NMDARs) involves their physical interaction with the non-selective cation channel, TRPM4, it has become possible to develop a new pharmacological principle for neuroprotection, namely the disruption of the NMDAR/TRPM4 death signaling complex. This can be accomplished through the expression of the TwinF domain, a 57-amino-acid-long stretch of TRPM4 that mediates its interaction with NMDARs, but also using small molecule TwinF interface (TI) inhibitors, also known as NMDAR/TRPM4 interaction interface inhibitors. Both TwinF and small molecule TI inhibitors detoxify extrasynaptic NMDARs without interfering with synaptic NMDARs, which serve important physiological functions in the brain. As the toxic signaling of extrasynaptic NMDARs contributes to a wide range of neurodegenerative conditions, TI inhibitors may offer therapeutic options for currently untreatable human neurodegenerative diseases including Amyotrophic Lateral Sclerosis, Alzheimer's disease, and Huntington's disease.

Memantine has a nicotinic neuroprotective pathway in acute hippocampal slices after an NMDA insult

Memantine is a non-competitive antagonist with a moderate affinity to the N-methyl-d-Aspartate (NMDA) receptor. The present study assessed memantine's neuroprotective activity using electrophysiology of ex-vivo hippocampal slices. Interestingly, a nicotinic component was necessary for memantine's neuroprotection (NP). Memantine demonstrated a bell-shaped dose-response curve of NP against NMDA. Memantine was neuroprotective at concentrations below 3 μM, but the NP declined at higher concentrations (>3 μM) when memantine inhibits the NMDA receptor. Additional evidence that memantine NP is mediated by an alternate mechanism independent of the inhibition of the NMDA receptor is supported by its ability to protect neurons when applied before or after the NMDA insult and in the presence of D(-)-2-Amino-5-phosphonopentanoic acid (APV), the standard NMDA receptor inhibitor. We found several similarities between the memantine NP mechanism and the neuroprotective nicotinic drug, the 4R cembranoid. Memantine's NP requires the release of acetylcholine, the activation of α4β2, and is independent of MEK/MAPK signaling. Both 4R and memantine require the activation of PI3K/AKT for NP against NMDA-mediated excitotoxicity, although at different concentrations. In conclusion, our studies show memantine is neuroprotective through a nicotinic pathway, similar to the nicotinic drug 4R. This information leads to a better understanding of memantine's mechanisms of action and explains its dose-dependent effectiveness in Alzheimer's and other neurological disorders.

Glutamate modulation for the treatment of levodopa induced dyskinesia: a brief review of the drugs tested in the clinic

Levodopa is the standard treatment for Parkinson's disease, but its use is marred by the emergence of dyskinesia, for which treatment options remain limited. Here, we review the glutamatergic modulators that were assessed for their antidyskinetic potential in clinical trials, including N-methyl-D-aspartate (NMDA) antagonists, agonists at the glycine-binding site on NMDA receptors, metabotropic glutamate (mGlu) 4 agonists, mGlu₅ antagonists, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) antagonists and glutamate release inhibitors. Several agents that were investigated are not selective for their targets, raising uncertainty about the extent to which glutamatergic modulation contributed to their effects. Except for amantadine, the use of glutamatergic modulators for the treatment of dyskinesia in Parkinson's disease remains largely investigational, with promising results obtained with mGlu₅ negative allosteric modulation.

Dequalinium chloride is an antagonists of α7 nicotinic acetylcholine receptors

Dequalinium chloride has been used primarily as antiseptic compounds, but recently has been investigated for its effects on specific targets, including muscarinic acetylcholine receptors. Here we investigated dequalinium chloride as an antagonist to α7 nicotinic acetylcholine receptors. The pharmacological properties of dequalinium were established using cell lines stably co-transfected with the calcium-permeable human α7 nicotinic acetylcholine receptors and its chaperone NACHO, calcium dye fluorescent measurements or a calcium-sensitive protein reporter, and patch clamp recording of ionic currents. Using calcium dye fluorescence plate reader measurements, we find dequalinium chloride is an antagonist of α7 nicotinic acetylcholine receptors with an IC₅₀ of 672 nM in response to activation with 500 μM acetylcholine chloride and positive allosteric modulator PNU-120596. However, using a membrane-tethered GCAMP7s calcium reporter allowed detection of α7-mediated calcium flux in the absence of PNU-120596. Using this approach revealed an IC₅₀ of 157 nM for dequalinium on 300 μM acetylcholine-evoked currents. Using patch clamp recordings with 300 μM acetylcholine chloride and 10 μM PNU-120596, we find lower concentrations are sufficient to block ionic currents, with IC₅₀ of 120 nM for dequalinium chloride and 54 nM for the related UCL 1684 compound. In summary, we find that dequalinium chloride and UCL1684, which are generally used to block SK-type potassium channels, are also highly effective antagonists of α7 nicotinic acetylcholine receptors. This finding, in combination with previous studies of muscarinic acetylcholine receptors, clearly establishes dequalinium compounds within the class of general anti-cholinergic antagonists.

Role of Pharmacogenomics in Individualizing Treatment for Alzheimer's Disease

The development of Alzheimer's disease therapeutics has been challenging, with 99% of clinical trials failing to find a significant difference between drug and placebo. While the quest continues for more effective treatments, there is emerging evidence that pharmacogenetic considerations are important factors in regard to metabolism, efficacy, and toxicity of drugs. Currently, there are five US Food and Drug Administration-approved drugs for the treatment of Alzheimer's disease; three acetylcholinesterase inhibitors, memantine, and aducanumab. Introducing a limited genetic panel consisting of APOE4, CYP2D6*10, and BChE*K would optimize acetylcholinesterase inhibitor therapy, facilitate immunotherapy risk assessment, and inform an amyloid-related imaging abnormality surveillance schedule. In view of the genetic heterogeneity of Alzheimer's disease identified in genome-wide association studies, pharmacogenetics is expected to play an increasing role in mechanism-specific treatment strategies and personalized medicine.

Unbalanced Regulation of α7 nAChRs by Ly6h and NACHO Contributes to Neurotoxicity in Alzheimer's Disease

α7 nicotinic acetylcholine receptors (nAChRs) are widely expressed in the brain where they promote fast cholinergic synaptic transmission and serve important neuromodulatory functions. However, their high permeability to Ca2+ also predisposes them to contribute to disease states. Here, using transfected HEK-tsa cells and primary cultured hippocampal neurons from male and female rats, we demonstrate that two proteins called Ly6h and NACHO compete for access to α7 subunits, operating together but in opposition to maintain α7 assembly and activity within a narrow range that is optimal for neuronal function and viability. Using mixed gender human temporal cortex and cultured hippocampal neurons from rats we further show that this balance is perturbed during Alzheimer's disease (AD) because of amyloid β (Aβ)-driven reduction in Ly6h, with severe reduction leading to increased phosphorylated tau and α7-mediated neurotoxicity. Ly6h release into human CSF is also correlated with AD severity. Thus, Ly6h links cholinergic signaling, Aβ and phosphorylated tau and may serve as a novel marker for AD progression.SIGNIFICANCE STATEMENT One of the earliest and most persistent hypotheses regarding Alzheimer's disease (AD) attributes cognitive impairment to loss of cholinergic signaling. More recently, interest has focused on crucial roles for amyloid β (Aβ) and phosphorylated tau in Alzheimer's pathogenesis. Here, we demonstrate that these elements are linked by Ly6h and its counterpart, NACHO, functioning in opposition to maintain assembly of nicotinic acetylcholine receptors (nAChRs) within the physiological range. Our data suggests that Aβ shifts the balance away from Ly6h and toward NACHO, resulting in increased assembly of Ca2+-permeable nAChRs and thus a conversion of basal cholinergic to neurotoxic signaling.

A multitude of signaling pathways associated with Alzheimer's disease and their roles in AD pathogenesis and therapy

The exact molecular mechanisms associated with Alzheimer's disease (AD) pathology continue to represent a mystery. In the past decades, comprehensive data were generated on the involvement of different signaling pathways in the AD pathogenesis. However, the utilization of signaling pathways as potential targets for the development of drugs against AD is rather limited due to the immense complexity of the brain and intricate molecular links between these pathways. Therefore, finding a correlation and cross-talk between these signaling pathways and establishing different therapeutic targets within and between those pathways are needed for better understanding of the biological events responsible for the AD-related neurodegeneration. For example, autophagy is a conservative cellular process that shows link with many other AD-related pathways and is crucial for maintenance of the correct cellular balance by degrading AD-associated pathogenic proteins. Considering the central role of autophagy in AD and its interplay with many other pathways, the finest therapeutic strategy to fight against AD is the use of autophagy as a target. As an essential step in this direction, this comprehensive review represents recent findings on the individual AD-related signaling pathways, describes key features of these pathways and their cross-talk with autophagy, represents current drug development, and introduces some of the multitarget beneficial approaches and strategies for the therapeutic intervention of AD.

Memantine Promotes Bactericidal Effect of Neutrophils Against Infection with Pseudomonas aeruginosa and Its Drug-Resistant Strain, by Improving Reactive Oxygen Species Generation

Pseudomonas aeruginosa is an opportunistic pathogen, which usually presents multiple antibiotic resistance. Host-directed therapy involves modulating the host defense system and the interplay between innate and adaptive immunity is a new strategy for designing anti-infection drugs. Memantine (MEM), a drug used to treat Alzheimer's disease, has a good inhibitory effect on neonatal mice with Escherichia coli-associated bacteremia and meningitis; however, the inhibitory effect and mechanisms of MEM against P. aeruginosa infection remain unclear. Here, we investigated whether MEM could inhibit P. aeruginosa infection and explored the potential mechanisms. MEM significantly promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain. The combination index of MEM and amikacin (AMK) was <1. In vivo experiments showed that the bacteremia and inflammation severities in the MEM-treated group were less than those in the untreated group, and the bacterial load in the organs was significantly less than that in the control group. Combining MEM with the reactive oxygen species (ROS) inhibitor, N-acetyl-l-cysteine, weakened the anti-infective effect of MEM. MEM increased the expression of NADPH p67phox and promoted neutrophilic ROS production. Deleting the p67phox gene significantly weakened the effects of MEM on ROS generation and improving bactericidal effect of neutrophils. In conclusion, MEM promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain, and had a synergistic antibacterial effect when combined with AMK. MEM may exert its anti-infective effects by promoting neutrophilic bactericidal activity via increasing the expression level of p67phox and further stimulating ROS generation.

Insight into Glutamatergic Involvement in Rewarding Effects of Mephedrone in Rats: In Vivo and Ex Vivo Study

Mephedrone is a widely used drug of abuse, exerting its effects by interacting with monoamine transporters. Although this mechanism has been widely studied heretofore, little is known about the involvement of glutamatergic transmission in mephedrone effects. In this study, we comprehensively evaluated glutamatergic involvement in rewarding effects of mephedrone using an interdisciplinary approach including (1) behavioural study on effects of memantine (non-selective NMDA antagonist) on expression of mephedrone-induced conditioned place preference (CPP) in rats; (2) evaluation of glutamate concentrations in the hippocampus of rats following 6 days of mephedrone administration, using in vivo magnetic resonance spectroscopy (MRS); and (3) determination of glutamate levels in the hippocampus of rats treated with mephedrone and subjected to MRS, using ion-exchange chromatography. In the presented research, we confirmed priorly reported mephedrone-induced rewarding effects in the CPP paradigm and showed that memantine (5 mg/kg) was able to reverse the expression of this effect. MRS study showed that subchronic mephedrone administration increased glutamate level in the hippocampus when measured in vivo 24 h (5 mg/kg, 10 mg/kg and 20 mg/kg) and 2 weeks (5 mg/kg and 20 mg/kg) after last injection. Ex vivo chromatographic analysis did not show significant changes in hippocampal glutamate concentrations; however, it showed similar results as obtained in the MRS study proving its validity. Taken together, the presented study provides new insight into glutamatergic involvement in rewarding properties of mephedrone.

DMV extrasynaptic NMDA receptors regulate caloric intake in rats

Acute high-fat diet (aHFD) exposure induces a brief period of hyperphagia before caloric balance is restored. Previous studies have demonstrated that this period of regulation is associated with activation of synaptic N-methyl-D-aspartate (NMDA) receptors on dorsal motor nucleus of the vagus (DMV) neurons, which increases vagal control of gastric functions. Our aim was to test the hypothesis that activation of DMV synaptic NMDA receptors occurs subsequent to activation of extrasynaptic NMDA receptors. Sprague-Dawley rats were fed a control or high-fat diet for 3-5 days prior to experimentation. Whole-cell patch-clamp recordings from gastric-projecting DMV neurons; in vivo recordings of gastric motility, tone, compliance, and emptying; and food intake studies were used to assess the effects of NMDA receptor antagonism on caloric regulation. After aHFD exposure, inhibition of extrasynaptic NMDA receptors prevented the synaptic NMDA receptor-mediated increase in glutamatergic transmission to DMV neurons, as well as the increase in gastric tone and motility, while chronic extrasynaptic NMDA receptor inhibition attenuated the regulation of caloric intake. After aHFD exposure, the regulation of food intake involved synaptic NMDA receptor-mediated currents, which occurred in response to extrasynaptic NMDA receptor activation. Understanding these events may provide a mechanistic basis for hyperphagia and may identify novel therapeutic targets for the treatment of obesity.

The α2δ-1-NMDAR1 interaction in the trigeminal ganglion contributes to orofacial ectopic pain following inferior alveolar nerve injury

Orofacial ectopic pain can often arise following nerve injury. However, the exact mechanism responsible for orofacial ectopic pain induced by trigeminal nerve injury remains unknown. The α2δ-1 and glutamate N-methyl-d-aspartic acid receptor (NMDAR) interactions have been demonstrated to participate in neuropathic pain regulation in the spinal cord. In this study, a rat model of inferior alveolar nerve transection (IANX) was used to investigate the role of α2δ-1-NMDAR1 interaction in the trigeminal ganglion (TG) in regard to the regulation of orofacial ectopic pain. Western blot (WB) analysis indicated that α2δ-1 and NMDAR1 in the TG were substantially higher in IANX rats than they were in sham/naive rats. Additionally, immunofluorescence (IF) results revealed that α2δ-1 and NMDAR1 were co-expressed and distributed within neurons and activated satellite glial cells in the TG. Co-immunoprecipitation (Co-IP) results indicated that α2δ-1-NMDAR1 complex levels in the TG were higher in IANX rats than they were in sham rats. Furthermore, the results of behavioral tests demonstrated that intra-TG injection of gabapentin (α2δ-1 inhibitory ligand) or memantine hydrochloride (NMDAR antagonist) reversed the decrease in mechanical head-withdrawal threshold (HWT) in IANX rats. Moreover, inhibition of α2δ-1 by intra-TG administration of gabapentin suppressed the upregulation of the NMDAR1 protein, and the inhibition of NMDAR by intra-TG administration of memantine hydrochloride inhibited the increased expression of α2δ-1 protein induced by IANX. In conclusion, the physical and functional interaction between α2δ-1 and NMDAR1 is critical for the development of orofacial ectopic pain, indicating that α2δ-1, NMDAR1, and the α2δ-1-NMDAR1 complex may represent potential targets for the treatment of orofacial ectopic pain.

Effect of Memantine on Pentylenetetrazol-induced Seizures and EEG Profile in Animal Model of Cortical Malformation

Developmental cortical malformations (DCM) are one of the main causes of refractory epilepsy. Many are the mechanisms underlying the hyperexcitability in DCM, including the important contribution of N-methyl-D-aspartate receptors (NMDAR). NMDAR blockers are shown to abolish seizures and epileptiform activity. Memantine, a NMDAR antagonist used to treat Alzheimeŕs disease, has been recently investigated as a possible treatment for other neurological disorders. However, the effects on preventing or diminishing seizures are controversial. Here we aimed to evaluate the effects of memantine on pentylenetetrazole (PTZ)-induced seizures in the freeze-lesion (FL) model. Bilateral cortical microgyria were induced (FL) or not (Sham) in male Wistar neonate rats. At P30, subdural electrodes were implanted and 7 days later, video-EEG was recorded in animals receiving either memantine (FL-M or Sham-M) or saline (FL-S or Sham-S), followed by PTZ. Seizures were evaluated by video-EEG during one hour and scored according to Racine scale. The video-EEG analyses revealed that the number of seizures and the total duration of stage IV-V seizures developed during the 1 h-period increased after memantine application in all groups. The EEG power spectral density (PSD) analysis showed an increased PSD of pre-ictal delta in Sham-M animals and increased PSD of slow, middle and fast gamma oscillations after memantine injection that persists during the pre-ictal period in all groups. Our findings suggested that memantine was unable to control the PTZ-induced seizures and that the associated enhancement of PSD of gamma oscillations may contribute to the increased probability of seizure development in these animals.

Treating disorders across the lifespan by modulating cholinergic signaling with galantamine

Advances in understanding the regulatory functions of the nervous system have revealed neural cholinergic signaling as a key regulator of cytokine responses and inflammation. Cholinergic drugs, including the centrally acting acetylcholinesterase inhibitor, galantamine, which are in clinical use for the treatment of Alzheimer's disease and other neurodegenerative and neuropsychiatric disorders, have been rediscovered as anti-inflammatory agents. Here, we provide a timely update on this active research and clinical developments. We summarize the involvement of cholinergic mechanisms and inflammation in the pathobiology of Alzheimer's disease, Parkinson's disease, and schizophrenia, and the effectiveness of galantamine treatment. We also highlight recent findings demonstrating the effects of galantamine in preclinical and clinical settings of numerous conditions and diseases across the lifespan that are characterized by immunological, neurological, and metabolic dysfunction.

Potentiation of cognitive enhancer effects of Alzheimer's disease medication memantine by alpha7 nicotinic acetylcholine receptor agonist PHA-543613 in the Morris water maze task

RATIONALE

There are controversial pieces of evidence whether combination therapies using memantine and cholinesterase inhibitors are beneficial over their monotreatments. However, results of preclinical studies are promising when memantine is combined with agonists and allosteric modulators of the alpha7 nicotinic acetylcholine receptor (nAChR).

OBJECTIVES

Here, we tested the hypothesis that cognitive enhancer effects of memantine can be potentiated through modulating alpha7 nAChRs in a scopolamine-induced amnesia model.

METHODS

Monotreatments, as well as co-administrations of selective alpha7 nicotinic acetylcholine receptor agonist PHA-543613 and memantine were tested in the Morris water maze task in rats. The efficacy of the co-administration treatment was observed on different domains of spatial episodic memory.

RESULTS

Low dose of memantine (0.1 mg/kg) and PHA-543613 (0.3 mg/kg) successfully reversed scopolamine-induced short-term memory deficits both in monotreatments and in co-administration. When recall of information from long-term memory was tested, pharmacological effects caused by co-administration of subeffective doses of memantine and PHA-543613 exceeded that of their monotreatments.

CONCLUSION

Our results further support the evidence of beneficial interactions between memantine and alpha7 nAChR ligands and suggest a prominent role of alpha7 nAChRs in the procognitive effects of memantine.

The potential for one drug, administered at the earliest preclinical stage, to prevent the subsequent decline of cognition that eventuates in dementia

In the process that eventuates in mild cognitive impairment (MCI) and ultimately in Alzheimer's dementia, the earliest identifiable change is in the function of synapses. If started at that early point in time, when there is subjective but not objective memory loss plus abnormal brain imaging with fluorodeoxyglucose and Pittsburgh compound B, treatment with a single drug directed at synaptic dysfunction might prevent development of cognitive impairment. Each of four drugs, dantrolene, lithium, minocycline, and piracetam, benefits synaptic impairment. This presentation has two sections. In the first, evidence is discussed at length, for abnormality in the axo-spinous synapse as being the earliest change before objective cognitive decline. The second section explains the benefits to synapses provided by the four mentioned drugs. Dantrolene and lithium perhaps have the strongest supporting data for use as single agents: their efficacy should be subjected to clinical trial.

Novel Therapeutic Approach for Excitatory/Inhibitory Imbalance in Neurodevelopmental and Neurodegenerative Diseases

Excitatory/inhibitory (E/I) balance, defined as the balance between excitation and inhibition of synaptic activity in a neuronal network, accounts in part for the normal functioning of the brain, controlling, for example, normal spike rate. In many pathological conditions, this fine balance is perturbed, leading to excessive or diminished excitation relative to inhibition, termed E/I imbalance, reflected in network dysfunction. E/I imbalance has emerged as a contributor to neurological disorders that occur particularly at the extremes of life, including autism spectrum disorder and Alzheimer's disease, pointing to the vulnerability of neuronal networks at these critical life stages. Hence, it is important to develop approaches to rebalance neural networks. In this review, we describe emerging therapies that can normalize the E/I ratio or the underlying abnormality that contributes to the imbalance in electrical activity, thus improving neurological function in these maladies.

Functional characterization of multifunctional ligands targeting acetylcholinesterase and alpha 7 nicotinic acetylcholine receptor

Alzheimer's disease (AD) is a neurodegenerative disorder associated with cholinergic dysfunction, provoking memory loss and cognitive dysfunction in elderly patients. The cholinergic hypothesis provided over the years with molecular targets for developing palliative treatments for AD, acting on the cholinergic system, namely, acetylcholinesterase and α7 nicotinic acetylcholine receptor (α7 nAChR). In our synthetic work, we used "click-chemistry" to synthesize two Multi Target Directed Ligands (MTDLs) MB105 and MB118 carrying tacrine and quinuclidine scaffolds which are known for their anticholinesterase and α7 nAChR agonist activities, respectively. Both, MB105 and MB118, inhibit human acetylcholinesterase and human butyrylcholinesterase in the nanomolar range. Electrophysiological recordings on Xenopus laevis oocytes expressing human α7 nAChR showed that MB105 and MB118 acted as partial agonists of the referred nicotinic receptor, albeit, with different potencies despite their similar structure. The different substitution at C-3 on the 2,3-disubstituted quinuclidine scaffold may account for the significantly lower potency of MB118 compared to MB105. Electrophysiological recordings also showed that the tacrine precursor MB320 behaved as a competitive antagonist of human α7 nAChR, in the micromolar range, while the quinuclidine synthetic precursor MB099 acted as a partial agonist. Taken all together, MB105 behaved as a partial agonist of α7 nAChR at concentrations where it completely inhibited human acetylcholinesterase activity paving the way for the design of novel MTDLs for palliative treatment of AD.

Alzheimer's Disease Therapeutic Approaches

Alzheimer's disease (AD) was first described and diagnosed by Dr. Alois Alzheimer in 1906 (Hippius and Neundorfer, Dialogues Clin Neurosc 5:101-108, 2003). According to World Health Organization (WHO), AD is the most common cause of dementia, accounting for as many as 60-70% of senile dementia cases and affecting 47.5 million people worldwide (data from 2015) (Dementia Fact Sheet No 362. http://who.int/mediacentre/factsheets/fs362/en/ ). The median survival time after the onset of dementia ranges from 3.3 to 11.7 years (Todd et al. Int J Geriatr Psychiatry 28:1109-1124, 2013). AD is characterized as a severe, chronic, incurable, and progressive neurodegenerative disorder, associated with memory loss and cognition impairment accompanied by abnormal behavior and personality changes (Godyn et al. Pharmacol Rep 68:127-138, 2016). AD is characterized by neuronal death, which usually correlates with the appearance of key neuropathological changes, including acetylcholine deficiency, glutamate excitotoxicity, extracellular deposition of β-amyloid (Aβ plaques), intracellular neurofibrillary tangles by hyperphosphorylated tau protein deposits, neuroinflammation, and widespread neuronal loss (Godyn et al. Pharmacol Rep 68:127-138, 2016; Graham et al. Annu Rev. Med 68:413-430, 2017). The discovery of the degeneration of cholinergic neurons and the reduction of acetylcholine levels in postmortem studies of patients resulted in the use of drugs that leads to the increase of acetylcholine levels in brain (Dubois et al. Lacet Neurol 13:614-629, 2014). At present there is no preventative or curative treatment that interferes with the development of the disease. However, in recent years progress was made in the development of cholinergic drugs which have a positive effect on disease progression. Nowadays, specific drugs that can inhibit the enzyme that degrades acetylcholine are used. The development of new effective drugs involves a difficult and time-consuming process, accompanied by a very high failure rate. In the absence of effective therapies, the estimated number of people with dementia will reach 115 to 131, five million by 2050 (Dubois et al. Lacet Neurol 13:614-629, 2014; Cummings et al. Alzheimers Res Ther 6:37, 2014). Novel therapies and new targets required for developing more effective drugs for the treatment of AD patients are urgently needed.

Chronic memantine decreases nicotine self-administration in rats

Neurobehavioral bases of tobacco addiction and nicotine reinforcement are complex, involving more than only nicotinic cholinergic or dopaminergic systems. Memantine is an NMDA glutamate antagonist used to improve cognitive function in people with Alzheimer's disease. Glutamate may be an important component of the reinforcing effects of nicotine, so memantine was evaluated as a potential smoking cessation aid. Two studies were conducted with adult female rats, one testing acute effects of memantine over a range of doses for changing nicotine self-administration and the other testing the chronic effects of memantine to reduce nicotine self-administration. Acute memantine injections slightly, but significantly, increased nicotine self-administration in a dose-related manner. In contrast, chronic memantine treatment significantly reduced nicotine self-administration. During the first day of memantine administration in the chronic study, nicotine self-administration was significantly elevated replicating the acute study. Starting in the second week of treatment there was a significant reduction of nicotine self-administration relative to controls. This was seen because memantine treatment prevented the increase in nicotine self-administration shown by controls. There even continued to be a memantine-induced lowered nicotine self-administration during the week after the cessation of memantine treatment. Memantine or other drugs affecting NMDA glutamate receptors may be useful aids to smoking cessation. Full efficacy for reducing nicotine self-administration was seen as the NMDA drug treatment is given chronically. Importantly, the effect persisted even after treatment is ended, indicating the high potential for NMDA glutamate receptors to impact nicotine addiction.

[Hypothermic Action of Oseltamivir Not Dependent on Its Anti-influenza Virus Action]

Although the anti-influenza virus drug oseltamivir ameliorates the fever of influenza, adverse events related to its hypothermic effect have been reported. We found that oseltamivir causes dose-dependent hypothermia in normal mice, and have been studying the pharmacological mechanisms responsible for 12 years. Oseltamivir blocks nicotinic cholinergic transmission at sympathetic ganglia and reduces sympathetic modulation of brown adipose tissue (BAT), a heat generator. Oseltamivir was found to target the ion channels of nicotinic acetylcholine receptors, as demonstrated by patch clamp experiments with cells expressing the human α3β4 nicotinic receptor. Metabolized oseltamivir carboxylate, which inhibits the influenza virus neuraminidase, did not elicit hypothermia and ion channel suppression. Body temperature was decreased by intracerebroventricular administration of oseltamivir. Because this hypothermic effect was inhibited by dopamine D₂ receptor blockade, it was suggested that oseltamivir centrally stimulates the D₂ receptor. In Japan, the package inserts for oseltamivir and amantadine indicate very similar adverse neuropsychiatric reactions for the two drugs (abnormal behavior, consciousness disturbance, convulsion, delirium, delusion, hallucination). A literature search revealed that in some previous studies, oseltamivir and amantadine were shown to block the ion channel systems and activate the dopaminergic nervous system via several mechanisms. Therefore the similarity of the adverse reactions elicited by oseltamivir and amantadine was considered attributable to their similar pharmacological effects.

Antagonizing α7 nicotinic receptors with methyllycaconitine (MLA) potentiates receptor activity and memory acquisition

α7 nicotinic acetylcholine receptors (α7nAChRs) have been targeted to improve cognition in different neurological and psychiatric disorders. Nevertheless, no α7nAChR activating ligand has been clinically approved. Here, we investigated the effects of antagonizing α7nAChRs using the selective antagonist methyllycaconitine (MLA) on receptor activity in vitro and cognitive functioning in vivo. Picomolar concentrations of MLA significantly potentiated receptor responses in electrophysiological experiments mimicking the in vivo situation. Furthermore, microdialysis studies showed that MLA administration substantially increased hippocampal glutamate efflux which is related to memory processes. Accordingly, pre-tetanus administration of low MLA concentrations produced longer lasting potentiation (long-term potentiation, LTP) in studies examining hippocampal plasticity. Moreover, low doses of MLA improved acquisition, but not consolidation memory processes in rats. While the focus to enhance cognition by modulating α7nAChRs lies on agonists and positive modulators, antagonists at low doses should provide a novel approach to improve cognition in neurological and psychiatric disorders.

Cognitive Enhancer Effects of Low Memantine Doses Are Facilitated by an Alpha7 Nicotinic Acetylcholine Receptor Agonist in Scopolamine-Induced Amnesia in Rats

Alpha7 nicotinic acetylcholine receptors (nAChRs) play an important role in learning and memory and are promising targets for pharmacological cognitive enhancement. Memantine, an approved substance for Alzheimer's disease treatment, is an antagonist of the N-Methyl-D-aspartate receptor (NMDAR) and also acts as an alpha7 nAChR antagonist. Here, we tested the interaction between an alpha7 nAChR agonist (PHA-543613) and memantine. Efficacy of memantine, PHA-543613, and their co-administration were investigated on the spatial working memory of rats using the spontaneous alternation paradigm in T-maze. Scopolamine-induced transient amnesia was used to model cognitive impairment. First, the dose-response relationship was assessed for memantine, and its lowest effective dose was found to be 0.1 mg/kg. Then, co-administration treatments with subeffective doses of the alpha7 nAChR agonist PHA-543613 and different doses of memantine were tested. The co-administration of subeffective drug doses significantly improved memory performance of the rats and reversed scopolamine-induced deficits. Interestingly, a higher than effective (0.3 mg/kg) dose of memantine did not increase performance in monotreatment, only in co-administration with PHA-543613. However, the co-administration of PHA-543613 did not further increase the efficacy of the previously effective monotreatment doses of memantine. Thus, the efficacy of memantine monotreatment and its co-administration with PHA-543613 converged to create a common ceiling effect, with an additive interaction found in the behavioral effects. These results suggest that memantine and PHA-543613 may exert their cognitive enhancer effects on the same target, possibly on the alpha7 nAChRs. Results also suggest possible benefits of a combination therapy with memantine and alpha7 nAChR agonists.

Rollercoaster ride of kynurenines: steering the wheel towards neuroprotection in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is associated with cerebral cognitive deficits exhibiting two cardinal hallmarks: accruement of extracellular amyloid plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. The currently accessible therapeutic armamentarium merely provides symptomatic relief. Therefore, the cry for prospective neuroprotective strategies seems to be the need of the hour. Areas covered: This review comprehensively establishes correlation between kynurenine pathway (KP) metabolites and AD with major emphasis on its two functionally contrasting neuroactive metabolites i.e. kynurenic acid (KYNA) and quinolinic acid (QUIN) and enlists various clinical studies which hold a potential for future therapeutics in AD. Also, major hypotheses of AD and mechanisms underlying them have been scrutinized with the aim to brush up the readers with basic pathology of AD. Expert opinion: KP is unique in itself as it holds two completely different domains i.e. neurotoxic QUIN and neuroprotective KYNA and disrupted equilibrium between the two has a hand in neurodegeneration. KYNA has long been demonstrated to be neuroprotective but lately being disparaged for cognitive side effects. But we blaze a trail by amalgamating the pharmacological mechanistic studies of KYNA in kinship with α7nAChRs, NMDARs and GABA which lends aid in favour of KA.

[Similarity of Clinically Significant Neuropsychiatric Adverse Reactions Listed in Package Inserts between the Anti-influenza Drugs Oseltamivir and Amantadine (Possibility Attributable to Common Pharmacological Effects)]

　The anti-influenza virus drug oseltamivir has been reported to have several pharmacological actions including blocking of nicotinic acetylcholine receptor channels and activation of the dopaminergic system. These pharmacological actions highly overlap those of amantadine, another anti-influenza virus drug authorized in Japan, and ester-type local anesthetics. Moreover, oseltamivir and amantadine can clinically induce similar adverse neuropsychiatric reactions. In the present study, from the database of the Pharmaceuticals and Medical Devices Agency (PMDA), we surveyed 2576 drugs for which neuropsychiatric side effects similar to those of oseltamivir, amantadine and local anesthetics (abnormal behavior, confusion, consciousness disturbance, convulsion, delirium, delusion, hallucination, myoclonus, tremor) are listed as "clinically significant adverse reactions", and found 327 that had at least one of these adverse reactions. Other neuraminidase inhibitors (laninamivir, peramivir and zanamivir) did not elicit such adverse reactions. By discussing the pharmacological effects of drugs that elicit these adverse reactions, we propose that the similarity of adverse neuropsychiatric reactions between oseltamivir and amantadine is possibly attributable to their common pharmacological effects.

Glutamatergic synapses in neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) are a group of diseases whose symptoms arise during childhood or adolescence and that impact several higher cognitive functions such as learning, sociability and mood. Accruing evidence suggests that a shared pathogenic mechanism underlying these diseases is the dysfunction of glutamatergic synapses. We summarize present knowledge on autism spectrum disorders (ASD), intellectual disability (ID), Down syndrome (DS), Rett syndrome (RS) and attention-deficit hyperactivity disorder (ADHD), highlighting the involvement of glutamatergic synapses and receptors in these disorders. The most commonly shared defects involve α-amino-3-hydroxy-5-methyl- 4-isoxazole propionic acid receptors (AMPARs), N-methyl-d-aspartate receptors (NMDARs) and metabotropic glutamate receptors (mGluRs), whose functions are strongly linked to synaptic plasticity, affecting both cell-autonomous features as well as circuit formation. Moreover, the major scaffolding proteins and, thus, the general structure of the synapse are often deregulated in neurodevelopmental disorders, which is not surprising considering their crucial role in the regulation of glutamate receptor positioning and functioning. This convergence of defects supports the definition of neurodevelopmental disorders as a continuum of pathological manifestations, suggesting that glutamatergic synapses could be a therapeutic target to ameliorate patient symptomatology.

A Role for Prefrontal Cortical NMDA Receptors in Murine Alcohol-Heightened Aggression

Alcohol is associated with nearly half of all violent crimes committed in the United States; yet, a potential neural basis for this type of pathological aggression remains elusive. Alcohol may act on N-methyl-d-aspartate receptors (NMDARs) within cortical circuits to impede processing and to promote aggression. Here, male mice were characterized as alcohol-heightened (AHAs) or alcohol non-heightened aggressors (ANAs) during resident-intruder confrontations after self-administering 1.0 g/kg alcohol (6% w/v) or water. Alcohol produced a pathological-like pattern of aggression in AHAs; these mice shifted their bites to more vulnerable locations on the body of a submissive animal, including the anterior back and ventrum after consuming alcohol. In addition, through immunoblotting, we found that AHAs overexpressed the NMDAR GluN2D subunit in the prefrontal cortex (PFC) as compared to ANAs while the two phenotypes expressed similar levels of GluN1, GluN2A and GluN2B. After identifying several behavioral and molecular characteristics that distinguish AHAs from ANAs, we tested additional mice for their aggression following preferential antagonism of GluN2D-containing NMDARs. In these experiments, groups of AHAs and ANAs self-administered 1.0 g/kg alcohol (6% w/v) or water before receiving intraperitoneal (i.p.) doses of ketamine or memantine, or infusions of memantine directly into the prelimbic (PLmPFC) or infralimbic medial PFC (ILmPFC). Moderate doses of IP ketamine, IP memantine, or intra-PLmPFC memantine increased aggression in AHAs, but only in the absence of alcohol. Prior alcohol intake blocked the pro-aggressive effects of ketamine or memantine. In contrast, only memantine, administered systemically or intra-PLmPFC, interacted with prior alcohol intake to escalate aggression in ANAs. Intra-ILmPFC memantine had no effect on aggression in either AHAs or ANAs. In sum, this work illustrates a potential role of GluN2D-containing NMDARs in the PLmPFC in alcohol-heightened aggression. GluN2D-containing NMDARs are highly expressed on cortical parvalbumin-containing interneurons, suggesting that, in a subset of individuals, alcohol may functionally alter signal integration within cortical microcircuits to dysregulate threat reactivity and promote aggression. This work suggests that targeting GluN2D-NMDARs may be of use in reducing the impact of alcohol-related violence in the human population.

Glutamate and Its Receptors as Therapeutic Targets for Migraine

There is substantial evidence indicating a role for glutamate in migraine. Levels of glutamate are higher in the brain and possibly also in the peripheral circulation in migraine patients, particularly during attacks. Altered blood levels of kynurenines, endogenous modulators of glutamate receptors, have been reported in migraine patients. Population genetic studies implicate genes that are involved with glutamate signaling in migraine, and gene mutations responsible for familial hemiplegic migraine and other familial migraine syndromes may influence glutamate signaling. Animal studies indicate that glutamate plays a key role in pain transmission, central sensitization, and cortical spreading depression. Multiple therapies that target glutamate receptors including magnesium, topiramate, memantine, and ketamine have been reported to have efficacy in the treatment of migraine, although with the exception of topiramate, the evidence for the efficacy of these therapies is not strong. Also, because all of these therapies have other mechanisms of action, it is not possible to conclude that the efficacy of these drugs is entirely due to their effects on glutamate receptors. Further studies are needed to more clearly delineate the possible roles of glutamate and its specific receptor subtypes in migraine and to identify new ways of targeting glutamate for migraine therapy.

Psychotomimetic-like behavioral effects of memantine in the mouse

A single administration of mice with memantine (1-amino-3,5-dimethyladamantane), a glutamatergic N-methyl-d-aspartate (NMDA) receptor antagonist, induced stereotyped behaviors in dose- and time-dependent manners. The predominant behavioral component of the stereotypy was a continuous, exaggerated sniffing which was accompanied by persistent locomotion. In contrast, a psychostimulant methamphetamine (METH) predominantly induced a stereotyped biting and other forms of intense stationary stereotypical behaviors. Memantine-induced stereotyped sniffing was attenuated by pretreatment with haloperidol, a dopamine D₂ receptor antagonist, in a dose-dependent manner. The memantine-induced stereotyped sniffing was also attenuated by pretreatment with betahistine (2-[2-(methylamino)ethyl]pyridine), an agent which increases histamine turnover and releases histamine in the brain. These observations suggest that memantine might induce stereotypies through neuronal mechanisms that are somewhat different from those of METH, but still overlap to a certain extent, since memantine-induced stereotypies can be attenuated by the mechanisms that also suppress METH-induced stereotypy. Importantly, these data suggests that the effects of memantine may be more limited to the ventral striatum including nucleus accumbens than those of METH, which is associated with dorsal striatal stimulation at high doses. In this respect memantine may also have pharmacological properties such as compartmentation (i.e. brain distribution) and neuronal mechanisms different from those of other NMDA receptor antagonists, such as ketamine, which may have important implications for therapeutic uses of these drugs.

Memantine for the Treatment of Dementia: A Review on its Current and Future Applications

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence in the brain of extracellular amyloid-β protein (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. The N-Methyl-D-aspartate receptors (NMDAR), ionotropic glutamate receptor, are essential for processes like learning and memory. An excessive activation of NMDARs has been associated with neuronal loss. The discovery of extrasynaptic NMDARs provided a rational and physiological explanation between physiological and excitotoxic actions of glutamate. Memantine (MEM), an antagonist of extrasynaptic NMDAR, is currently used for the treatment of AD jointly with acetylcholinesterase inhibitors. It has been demonstrated that MEM preferentially prevents the excessive continuous extrasynaptic NMDAR disease activation and therefore prevents neuronal cell death induced by excitotoxicity without disrupting physiological synaptic activity. The problem is that MEM has shown no clear positive effects in clinical applications while, in preclinical stages, had very promising results. The data in preclinical studies suggests that MEM has a positive impact on improving AD brain neuropathology, as well as in preventing Aβ production, aggregation, or downstream neurotoxic consequences, in part through the blockade of extrasynaptic NMDAR. Thus, the focus of this review is primarily to discuss the efficacy of MEM in preclinical models of AD, consider possible combinations of this drug with others, and then evaluate possible reasons for its lack of efficacy in clinical trials. Finally, applications in other pathologies are also considered.

Central inhibition of initiation of swallowing by systemic administration of diazepam and baclofen in anaesthetized rats

Dysphagia is caused not only by neurological and/or structural damage but also by medication. We hypothesized memantine, dextromethorphan, diazepam, and baclofen, all commonly used drugs with central sites of action, may regulate swallowing function. Swallows were evoked by upper airway (UA)/pharyngeal distension, punctate mechanical stimulation using a von Frey filament, capsaicin or distilled water (DW) applied topically to the vocal folds, and electrical stimulation of a superior laryngeal nerve (SLN) in anesthetized rats and were documented by recording electromyographic activation of the suprahyoid and thyrohyoid muscles and by visualizing laryngeal elevation. The effects of intraperitoneal or topical administration of each drug on swallowing function were studied. Systemic administration of diazepam and baclofen, but not memantine or dextromethorphan, inhibited swallowing evoked by mechanical, chemical, and electrical stimulation. Both benzodiazepines and GABA_A receptor antagonists diminished the inhibitory effects of diazepam, whereas a GABA_B receptor antagonist diminished the effects of baclofen. Topically applied diazepam or baclofen had no effect on swallowing. These data indicate that diazepam and baclofen act centrally to inhibit swallowing in anesthetized rats.NEW & NOTEWORTHY Systemic administration of diazepam and baclofen, but not memantine or dextromethorphan, inhibited swallowing evoked by mechanical, chemical, and electrical stimulation. Both benzodiazepines and GABA_A receptor antagonists diminished the inhibitory effects of diazepam, whereas a GABA_B receptor antagonist diminished the effects of baclofen. Topical applied diazepam or baclofen was without effect on swallowing. Diazepam and baclofen act centrally to inhibit swallowing in anesthetized rats.

Therapeutics of Neurotransmitters in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease, characterized by the loss of memory, multiple cognitive impairments and changes in the personality and behavior. Several decades of intense research have revealed that multiple cellular changes are involved in disease process, including synaptic damage, mitochondrial abnormalities and inflammatory responses, in addition to formation and accumulation of amyloid-β (Aβ) and phosphorylated tau. Although tremendous progress has been made in understanding the impact of neurotransmitters in the progression and pathogenesis of AD, we still do not have a drug molecule associated with neurotransmitter(s) that can delay disease process in elderly individuals and/or restore cognitive functions in AD patients. The purpose of our article is to assess the latest developments in neurotransmitters research using cell and mouse models of AD. We also updated the current status of clinical trials using neurotransmitters' agonists/antagonists in AD.

Gene, Stem Cell, and Alternative Therapies for SCA 1

Spinocerebellar ataxia 1 is an autosomal dominant disease characterized by neurodegeneration and motor dysfunction. In disease pathogenesis, polyglutamine expansion within Ataxin-1, a gene involved in transcriptional repression, causes protein nuclear inclusions to form. Most notably, neuronal dysfunction presents in Purkinje cells. However, the effect of mutant Ataxin-1 is not entirely understood. Two mouse models are employed to represent spinocerebellar ataxia 1, a B05 transgenic model that specifically expresses mutant Ataxin-1 in Purkinje cells, and a Sca1 154Q/2Q model that inserts the polyglutamine expansion into the mouse Ataxin-1 locus so that the mutant Ataxin-1 is expressed in all cells that express Ataxin-1. This review aims to summarize and evaluate the wide variety of therapies proposed for spinocerebellar ataxia 1, specifically gene and stem cell therapies.

Ethanol preconditioning of rat cerebellar cultures targets NMDA receptors to the synapse and enhances peroxiredoxin 2 expression

Epidemiological studies indicate that light-moderate alcohol (ethanol) consumers tend to have reduced risks of cognitive impairment and progression to dementia during aging. Exploring possible mechanisms, we previously found that moderate ethanol preconditioning (MEP, 20-30mM) of rat brain cultures for several days instigated neuroprotection against β-amyloid peptides. Our biochemical evidence implicated the NMDA receptor (NMDAR) as a potential neuroprotective "sensor", specifically via synaptic NMDAR signaling. It remains unclear how ethanol modulates the receptor and its downstream targets to engender neuroprotection. Here we confirm with deconvolution microscopy that MEP of rat mixed cerebellar cultures robustly increases synaptic NMDAR localization. Phospho-activation of the non-receptor tyrosine kinases Src and Pyk2, known to be linked to synaptic NMDAR, is also demonstrated. Additionally, the preconditioning enhances levels of an antioxidant protein, peroxiredoxin 2 (Prx2), reported to be downstream of synaptic NMDAR signaling, and NMDAR antagonism with memantine (earlier found to abrogate MEP neuroprotection) blocks the Prx2 elevations. To further link Prx2 with antioxidant-based neuroprotection, we circumvented the ethanol preconditioning-NMDAR pathway by pharmacologically increasing Prx2 with the naturally-occurring cruciferous compound, 3H-1,2-dithiole-3-thione (D3T). Thus, D3T pretreatment elevated Prx2 expression to a similar extent as MEP, while concomitantly preventing β-amyloid neurotoxicity; D3T also protected the cultures from hydrogen peroxide toxicity. The findings support a mechanism that couples synaptic NMDAR signaling, Prx2 expression and augmented antioxidant defenses in ethanol preconditioning-induced neuroprotection. That this mechanism can be emulated by a cruciferous vegetable constituent suggests that such naturally-occurring "neutraceuticals" may be useful in therapy for oxidative stress-related dementias.

Protection by sigma-1 receptor agonists is synergic with donepezil, but not with memantine, in a mouse model of amyloid-induced memory impairments

Drugs activating the sigma-1 (σ1) chaperone protein are anti-amnesic and neuroprotective in neurodegenerative pathologies like Alzheimer's disease (AD). Since these so-called σ1 receptor (σ1R) agonists modulate cholinergic and glutamatergic systems in a variety of physiological responses, we addressed their putative additive/synergistic action in combination with cholinergic or glutamatergic drugs. The selective σ1 agonist PRE-084, or the non-selective σ1 drug ANAVEX2-73 was combined with the acetylcholinesterase inhibitor donepezil or the NMDA receptor antagonist memantine in the nontransgenic mouse model of AD-like memory impairments induced by intracerebroventricular injection of oligomeric Aβ25-35 peptide. Two behavioral tests, spontaneous alternation and passive avoidance response, were used in parallel and both protective and symptomatic effects were examined. After determination of the minimally active doses for each compound, the combinations were tested and the combination index (CI) calculated. Combinations between the σ1 agonists and donepezil showed a synergic protective effect, with CI<1, whereas the combinations with memantine showed an antagonist effect, with CI>1. Symptomatic effects appeared only additive for all combinations, with CI=1. A pharmacological analysis of the PRE-084+donepezil combination revealed that the synergy could be due to an inter-related mechanism involving α7 nicotinic ACh receptors and σ1R. These results demonstrated that σ1 drugs do not only offer a protective potential alone but also in combination with other therapeutic agents. The nature of neuromodulatory molecular chaperone of the σ1R could eventually lead to synergistic combinations.

Substantial Neuroprotective and Neurite Outgrowth-Promoting Activities by Bis(propyl)-cognitin via the Activation of Alpha7-nAChR, a Promising Anti-Alzheimer's Dimer

The cause of Alzheimer's disease (AD) could be ascribed to the progressive loss of functional neurons in the brain, and hence, agents with neuroprotection and neurite outgrowth-promoting activities that allow for the replacement of lost neurons may have significant therapeutic value. In the current study, the neuroprotective and the neurite outgrowth-promoting activities and molecular mechanisms of bis(propyl)-cognitin (B3C), a multifunctional anti-AD dimer, were investigated. Briefly, B3C (24 h pretreatment) fully protected against glutamate-induced neuronal death in primary cerebellar granule neurons with an IC50 value of 0.08 μM. The neuroprotection of B3C could be abrogated by methyllycaconitine, a specific antagonist of alpha7-nicotinic acetylcholine receptor (α7-nAChR). In addition, B3C significantly promoted neurite outgrowth in both PC12 cells and primary cortical neurons, as evidenced by the increase in the percentage of cells with extended neurites as well as the up-regulation of neuronal markers growth-associated protein-43 and β-III-tubulin. Furthermore, B3C rapidly upregulated the phosphorylation of extracellular signal-regulated kinase (ERK), a critical signaling molecule in neurite outgrowth that is downstream of the α7-nAChR signal pathway. Specific inhibitors of ERK and α7-nAChR, but not those of p38 mitogen-activated protein kinase and c-Jun NH(2)-terminal kinase, blocked the neurite outgrowth as well as ERK activation in PC12 cells induced by B3C. Most importantly, genetic depletion of α7-nAChR significantly abolished B3C-induced neurite outgrowth in PC12 cells. Taken together, our results suggest that B3C provided neuroprotection and neurite outgrowth-promoting activities through the activation of α7-nAChR, which offers a novel molecular insight into the potential application of B3C in AD treatment.