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

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.

Increased brain cytokine level associated impairment of vigilance and memory in aged rats can be alleviated by alpha7 nicotinic acetylcholine receptor agonist treatment

Age-related neurocognitive disorders are common problems in developed societies. Aging not only affects memory processes, but may also disturb attention, vigilance, and other executive functions. In the present study, we aimed to investigate age-related cognitive deficits in rats and associated molecular alterations in the brain. We also aimed to test the effects of the alpha7 nicotinic acetylcholine receptor (nAChR) agonist PHA-543613 on memory as well as on the sustained attention and vigilance of aged rats. Short- and long-term spatial memories of the rats were tested using the Morris water maze (MWM) task. To measure attention and vigilance, we designed a rat version of the psychomotor vigilance task (PVT) that is frequently used in human clinical examinations. At the end of the behavioral experiments, mRNA and protein expression of alpha7 nAChRs, cytokines, and brain-derived neurotrophic factor (BDNF) were quantitatively measured in the hippocampus, frontal cortex, striatum, and cerebellum. Aged rats showed marked cognitive deficits in both the MWM and the PVT. The deficit was accompanied by increased IL-1beta and TNFalpha mRNA expression and decreased BDNF protein expression in the hippocampus. PHA-543613 significantly improved the reaction time of aged rats in the PVT, especially for unexpectedly appearing stimuli, while only slightly (non-significantly) alleviating spatial memory deficits in the MWM. These results indicate that targeting alpha7 nAChRs may be an effective strategy for the amelioration of attention and vigilance deficits in age-related neurocognitive disorders.

The Proof-of-Concept of MBA121, a Tacrine-Ferulic Acid Hybrid, for Alzheimer's Disease Therapy

Great effort has been devoted to the synthesis of novel multi-target directed tacrine derivatives in the search of new treatments for Alzheimer's disease (AD). Herein we describe the proof of concept of MBA121, a compound designed as a tacrine-ferulic acid hybrid, and its potential use in the therapy of AD. MBA121 shows good β-amyloid (Aβ) anti-aggregation properties, selective inhibition of human butyrylcholinesterase, good neuroprotection against toxic insults, such as Aβ1-40, Aβ1-42, and H2O2, and promising ADMET properties that support translational developments. A passive avoidance task in mice with experimentally induced amnesia was carried out, MBA121 being able to significantly decrease scopolamine-induced learning deficits. In addition, MBA121 reduced the Aβ plaque burden in the cerebral cortex and hippocampus in APPswe/PS1ΔE9 transgenic male mice. Our in vivo results relate its bioavailability with the therapeutic response, demonstrating that MBA121 is a promising agent to treat the cognitive decline and neurodegeneration underlying AD.

Relationships and Interactions between Ionotropic Glutamate Receptors and Nicotinic Receptors in the CNS

Although ionotropic glutamate receptors and nicotinic receptors for acetylcholine (ACh) have usually been studied separately, they are often co-localized and functionally inter-dependent. The objective of this review is to survey the evidence for interactions between the two receptor families and the mechanisms underlying them. These include the mutual regulation of subunit expression, which change the NMDA:AMPA response balance, and the existence of multi-functional receptor complexes which make it difficult to distinguish between individual receptor sites, especially in vivo. This is followed by analysis of the functional relationships between the receptors from work on transmitter release, cellular electrophysiology and aspects of behavior where these can contribute to understanding receptor interactions. It is clear that nicotinic receptors (nAChRs) on axonal terminals directly regulate the release of glutamate and other neurotransmitters, α7-nAChRs generally promoting release. Hence, α7-nAChR responses will be prevented not only by a nicotinic antagonist, but also by compounds blocking the indirectly activated glutamate receptors. This accounts for the apparent anticholinergic activity of some glutamate antagonists, including the endogenous antagonist kynurenic acid. The activation of presynaptic nAChRs is by the ambient levels of ACh released from pre-terminal synapses, varicosities and glial cells, acting as a 'volume neurotransmitter' on synaptic and extrasynaptic sites. In addition, ACh and glutamate are released as CNS co-transmitters, including 'cholinergic' synapses onto spinal Renshaw cells. It is concluded that ACh should be viewed primarily as a modulator of glutamatergic neurotransmission by regulating the release of glutamate presynaptically, and the location, subunit composition, subtype balance and sensitivity of glutamate receptors, and not primarily as a classical fast neurotransmitter. These conclusions and caveats should aid clarification of the sites of action of glutamate and nicotinic receptor ligands in the search for new centrally-acting drugs.

Contributions of animal models of cognitive disorders to neuropsychopharmacology

Cognitive disorders and symptoms are key features of many mental and neurological diseases, with a large spectrum of impaired domains. Because of their possible evolution and detrimental functioning impact, they are a major pharmacological target for both symptomatic and disease-modifier drugs, while few cognitive enhancers have been marketed with an insufficient efficiency. It explains the need to model these cognitive disorders beyond the modelization of mental or neurological diseases themselves. According to the experimental strategy used to induce cognitive impairment, three categories of models have been identified: neurotransmission-driven models; pathophysiology-driven models; environment-driven models. These three categories of models reflect different levels of integration of endogenous and exogenous mechanisms underlying cognitive disorders in humans. Their comprehensive knowledge and illustration of their pharmacological modulation could help to propose a renewing strategy of drug development in central nervous system (CNS) field at a time when the academic and industrial invest seems to be declining despite the medical and social burden of brain diseases.

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.

Alpha7 nicotinic-N-methyl-D-aspartate hypothesis in the treatment of schizophrenia and beyond

Development of novel treatments for positive, cognitive, and negative symptoms continue to be a high-priority area of schizophrenia research and a major unmet clinical need. Given that all randomized controlled trials (RCTs) conducted to date failed with one add-on medication/mechanism of action, future RCTs with the same approach are not warranted. Even if the field develops a medication for cognition, others are still needed to treat negative and positive symptoms. Therefore, fixing one domain does not completely solve the problem. Also, targeting the cholinergic system, glutamatergic system, and cholinergic plus alpha7 nicotinic and N-methyl-D-aspartate (NMDA) receptors failed independently. Hence, targeting other less important pathophysiological mechanisms/targets is unlikely to be successful. Meta-analyses of RCTs targeting major pathophysiological mechanisms have found some efficacy signal in schizophrenia; thus, combination treatments with different mechanisms of action may enhance the efficacy signal. The objective of this article is to highlight the importance of conducting RCTs with novel combination treatments in schizophrenia to develop antischizophrenia treatments. Positive RCTs with novel combination treatments that target the alpha7 nicotinic and NMDA receptors simultaneously may lead to a disease-modifying therapeutic armamentarium in schizophrenia. Novel combination treatments that concurrently improve the three domains of psychopathology and several prognostic and theranostic biomarkers may facilitate therapeutic discovery in schizophrenia.

How do stupendous cannabinoids modulate memory processing via affecting neurotransmitter systems?

In the present study, we wanted to review the role of cannabinoids in learning and memory in animal models, with respect to their interaction effects with six principal neurotransmitters involved in learning and memory including dopamine, glutamate, GABA (γ-aminobutyric acid), serotonin, acetylcholine, and noradrenaline. Cannabinoids induce a wide-range of unpredictable effects on cognitive functions, while their mechanisms are not fully understood. Cannabinoids in different brain regions and in interaction with different neurotransmitters, show diverse responses. Previous findings have shown that cannabinoids agonists and antagonists induce various unpredictable effects such as similar effect, paradoxical effect, or dualistic effect. It should not be forgotten that brain neurotransmitter systems can also play unpredictable roles in mediating cognitive functions. Thus, we aimed to review and discuss the effect of cannabinoids in interaction with neurotransmitters on learning and memory. In addition, we mentioned to the type of interactions between cannabinoids and neurotransmitter systems. We suggested that investigating the type of interactions is a critical neuropharmacological issue that should be considered in future studies.

Galantamine-Memantine combination in the treatment of Alzheimer's disease and beyond

Alzheimer's disease (AD) is the most prevalent form of dementia in the elderly population worldwide. Despite the major unmet clinical need, no new medications for the treatment of AD have been approved since 2003. Galantamine is an acetylcholinesterase inhibitor that is also a positive allosteric modulator at the α4β2 and α7nACh receptors. Memantine is an N-methyl-d-aspartate receptor modulator/agonist. Both galantamine and memantine are FDA-approved medications for the treatment of AD. The objective of this review is to highlight the potential of the galantamine-memantine combination to conduct randomized controlled trials (RCTs) in AD. Several studies have shown the combination to be effective. Neurodegenerative diseases involve multiple pathologies; therefore, combination treatment appears to be a rational approach. Although underutilized, the galantamine-memantine combination is the standard of care in the treatment of AD. Positive RCTs with the combination with concurrent improvement in symptoms and biomarkers may lead to FDA approval, which may lead to greater utilization of this combination in clinical practice.

Delay-dependent cholinergic modulation of visual short-term memory in rhesus macaques

Cholinergic neuromodulation is known to play a key role in visual working memory (VWM) - keeping relevant stimulus representations available for cognitive processes for short time periods (up to a few minutes). Despite the growing body of evidence on how the neural and cognitive mechanisms of VWM dynamically change over retention time, there is mixed evidence available on cholinergic effects as a function of VWM delay period in non-human primates. Using the delayed matching to sample VWM task in rhesus macaques (N = 6), we aimed to characterize VWM maintenance in terms of performance changes as a function of delay duration (across a wide range of delays from 1 to 76 s). Then, we studied how cholinergic neuromodulation influences VWM maintenance using the muscarinic receptor antagonist scopolamine administered alone as transient amnestic treatment, and in combination with two doses of the acetylcholinesterase inhibitor donepezil, a widely used Alzheimer's medication probing for the reversal of scopolamine-induced impairments. Results indicate that scopolamine-induced impairments of VWM maintenance are delay-dependent and specifically affect the 15-33 s time range, suggesting that scopolamine worsens the normal decay of VWM with the passage of time. Donepezil partially rescued the observed scopolamine-induced impairments of VWM performance. These results provide strong behavioral evidence for the role of increased cholinergic tone and muscarinic neuromodulation in the maintenance of VWM beyond a few seconds, in line with our current knowledge on the role of muscarinic acetylcholine receptors in sustained neural activity during VWM delay periods.

Contribution of cholinergic system and Nrf2/HO-1 signaling to the anti-amnesic action of 7-fluoro-1,3-diphenylisoquinoline-1-amine in mice

The isoquinoline 7-fluoro-1,3-diphenylisoquinoline-1-amine (FDPI) has been studied due to its multitarget properties, such as modulation of GABAergic and glutamatergic systems, antioxidant, and anti-inflammatory. This study investigated the contribution of oxidative stress, nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/heme oxygenase (HO-1) signaling, and the cholinergic system to the anti-amnesic action of FDPI in mice. Adult male Swiss mice received FDPI for 5 days (5-25 mg/kg, i.g.); the animals received scopolamine (1 mg/kg, i.p) from day 3-5. The vehicle-control group was carried out. Afterward, mice performed object recognition tests (ORTs). Scopolamine induced amnesia and cholinergic dysfunction by increasing the acetylcholinesterase (AChE) activity and content, decreasing the muscarinic M1 receptor levels in the prefrontal cortex and hippocampus of mice. This study reveals that scopolamine altered oxidative stress parameters differently in the prefrontal cortex and hippocampus of mice. Whereas the prefrontal cortex was susceptible to oxidative stress, none of the parameters evaluated was altered in the hippocampus of scopolamine-treated mice. FDPI at doses of 10 and 25 mg/kg had an anti-amnesic effect in the ORT tests. FDPI 10 mg/kg reversed the increase in the AChE activity and content, oxidative stress parameters, and modulated Nrf2/HO-1 signaling in the prefrontal cortex of scopolamine-exposed mice. Pearson's correlation analyses reinforced the contribution of the prefrontal cortical cholinergic system, oxidative stress as well as Nrf2/HO-1 signaling in the anti-amnesic effect of FDPI. Considering FDPI effects on the hippocampus, it was effective against the cholinergic dysfunction, AChE activity and content, and M1 receptor levels, which collectively could contribute to its anti-amnesic effect.

Facilitation and inhibition of firing activity and N-methyl-D-aspartate-evoked responses of CA1 hippocampal pyramidal cells by alpha7 nicotinic acetylcholine receptor selective compounds in vivo

Alpha7 nicotinic acetylcholine receptors (nAChRs) are promising novel targets for the treatment of neurocognitive disorders. Although the cognitive enhancer potential of alpha7 nAChR agonists and positive allosteric modulators (PAMs) has been confirmed in several preclinical animal models, there are only sparse in vivo electrophysiological data on their effects on the firing activity and excitability of neurons. The present study investigated and compared local effects of alpha7 nAChR agonist PHA-543613 and PAMs PNU-120596 and NS-1738 on the spontaneous and N-methyl-D-aspartate-evoked (NMDA-evoked) firing rate of rat CA1 hippocampal pyramidal cells, in vivo. Furthermore, effects of alpha7 nAChR antagonist methyllycaconitine (MLA) and GABA were also tested. Results showed substantially different effects of the alpha7 nAChR agonist and PAMs. While PNU-120596 and NS-1738 predominantly and significantly increased both spontaneous and NMDA-evoked firing rate of the neurons, application of PHA-543613 resulted in almost equal distribution of facilitatory and inhibitory effects. The increase of the NMDA-evoked firing rate exerted by NS-1738 was superadditive over the sum of the single effects of NMDA and NS-1738. The simultaneous application of alpha7 nAChR agonist PHA-543613 and PAM NS-1738 resulted in additive increase of both spontaneous and NMDA-evoked firing rate. However, NS-1738 counteracted inhibitory effects of PHA-543613 in 5 out of 6 neurons, resulting in a synergistic potentiation of their firing responses to NMDA. Our results suggest that alpha7 nAChR PAMs increase neuronal excitability more potently than agonists, while the remarkable occurrence of inhibitory effects of PHA-543613 (possibly originating from receptor desensitization) implies that agonists may exert neuroprotective effects.

Galantamine-Memantine Combination as an Antioxidant Treatment for Schizophrenia

PURPOSE OF REVIEW

The objective of this article is to highlight the potential role of the galantamine-memantine combination as a novel antioxidant treatment for schizophrenia.

RECENT FINDINGS

In addition to the well-known mechanisms of action of galantamine and memantine, these medications also have antioxidant activity. Furthermore, an interplay exists between oxidative stress, inflammation (redox-inflammatory hypothesis), and kynurenine pathway metabolites. Also, there is an interaction between brain-derived neurotrophic factor and oxidative stress in schizophrenia. Oxidative stress may be associated with positive, cognitive, and negative symptoms and impairments in white matter integrity in schizophrenia. The antipsychotic-galantamine-memantine combination may provide a novel strategy in schizophrenia to treat positive, cognitive, and negative symptoms.

SUMMARY

A "single antioxidant" may be inadequate to counteract the complex cascade of oxidative stress. The galantamine-memantine combination as "double antioxidants" is promising. Hence, randomized controlled trials are warranted with the antipsychotic-galantamine-memantine combination with oxidative stress and antioxidant biomarkers in schizophrenia.