Memantine partly rescues behavioral and cognitive deficits in an animal model of neurodegeneration

Deciphering the dual role of N-methyl-D-Aspartate receptor in postoperative cognitive dysfunction: A comprehensive review

Postoperative cognitive dysfunction (POCD) is a common complication following surgery, adversely impacting patients' recovery, increasing the risk of negative outcomes, prolonged hospitalization, and higher mortality rates. The N-methyl-D-aspartate (NMDA) receptor, crucial for learning, memory, and synaptic plasticity, plays a significant role in the development of POCD. Various perioperative factors, including age and anesthetic use, can reduce NMDA receptor function, while surgical stress, inflammation, and pain may lead to its excessive activation. This review consolidates preclinical and clinical research to explore the intricate relationship between perioperative factors affecting NMDA receptor functionality and the onset of POCD. It discusses the influence of aging, anesthetic administration, perioperative injury, pain, and inflammation on the NMDA receptor-related pathophysiology of POCD. The comprehensive analysis presented aims to identify effective treatment targets for POCD, contributing to the improvement of patient outcomes post-surgery.

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.

Neurochemical changes underlying cognitive impairment in olfactory bulbectomized rats and the impact of the mGlu5-positive allosteric modulator CDPPB

The olfactory bulbectomized (OBX) rat model is a well-established model of depression in which antidepressant drugs reverse deficits in the passive avoidance test 14 days after administration. Recently, the olfactory bulbectomized rat model has been proposed to be a model of Alzheimer's disease (AD), and the available data indicate similarities between the changes that typically occur in AD and those observed in OBX animals. In the present study, the occurrence of neurochemical impairments related to AD were investigated 8 months after OB ablation. The expression of the nitric oxide synthases eNOS and nNOS, receptor for advanced glycation endproducts (RAGEs) and dimethylarginine dimethylaminohydrolase (DDAH1) in the prefrontal cortices (PFCs), hippocampi and striata of olfactory bulbectomized and sham-operated rats was evaluated. Subsequently, the impact of the administration of a positive allosteric modulator of the mGlu₅ receptor, CDPPB (14 days, 2.5 or 5 mg/kg), on OBX-related changes was assessed. OB ablation induced typical deficits in passive avoidance. Significant aberrations in the expression of both isoforms of NOS were observed in the hippocampus and striatum, and the expression of DDAH1 was increased in the PFCs of OBX animals. CDPPB at a dose of 5 mg/kg ameliorated cognitive impairment in the passive avoidance test and partially reversed the changes in eNOS and nNOS expression induced by the lesion. The results of this study confirm that some of the neurochemical changes observed in OBX animals may resemble those associated with AD pathology and that activation of the mGlu₅ receptor may partially counteract these pathological alterations.

SARS-CoV-2 infection in patients with serious mental illness and possible benefits of prophylaxis with Memantine and Amantadine

Patients with serious mental illness are a high-risk category of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Patients with schizophrenia are not participatory and have increased mortality and morbidity, patients with dementia cannot be cared for while depression, anxiety, bipolar tubing are associated with low immune status. Social stress is amplified by social isolation, amplifying depression and the mechanisms of decreased immunity. Hygiene measures and prophylactic behavior are impossible to put into practice in conditions of chronic mental illness. In coronavirus disease 2019 (COVID-19), the risk for severe development is associated with the presence of comorbidities and immune system deficiency. Prothrombotic status, cytokine storm and alveolar destruction are mechanisms that aggravate the evolution of patients, especially in the context in which they have dysfunction of the autonomic system. The activity of proinflammatory cytokines is accentuated by hyperglutamatergia, which potentiates oxidative stress and triggers the mechanisms of neural apoptosis by stimulating microglial activation. Activation of M1-type microglia has an important role in pathogenesis of major psychiatric disorders, such as major depression, schizophrenia or bipolar disorder, and may associate hippocampal atrophy and disconnection of cognitive structures. Memantine and Amantadine, N-methyl-D-aspartate (NMDA) glutamate receptor inhibitors, have demonstrated, through their pharmacological profile, psychotropic effects but also antiviral properties. In the conditions of the COVID-19 pandemic, based on these arguments, we suggest that they can be associated with the therapy with the basic psychotropics, Memantine or Amantadine, for the control of neuropsychiatric symptoms but also as adjuvants with antiviral action.

The Wistar-Kyoto rat model of endogenous depression: A tool for exploring treatment resistance with an urgent need to focus on sex differences

Major depressive disorder (MDD) is one of the leading causes of years lived with disability and contributor to the burden of disease worldwide. The incidence of MDD has increased by ~20% in the last decade. Currently antidepressant drugs such as the popular selective serotonin reuptake inhibitors (SSRIs) are the leading form of pharmaceutical intervention for the treatment of MDD. SSRIs however, are inefficient in ameliorating depressive symptoms in ~50% of patients and exhibit a prolonged latency of efficacy. Due to the burden of disease, there is an increasing need to understand the neurobiology underpinning MDD and to discover effective treatment strategies. Endogenous models of MDD, such as the Wistar-Kyoto (WKY) rat provide a valuable tool for investigating the pathophysiology of MDD. The WKY rat displays behavioural and neurobiological phenotypes similar to that observed in clinical cases of MDD, as well as resistance to common antidepressants. Specifically, the WKY strain exhibits increased anxiety- and depressive-like behaviours, as well as alterations in Hypothalamic Pituitary Adrenal (HPA) axis, serotonergic, dopaminergic and neurotrophic systems with emerging studies suggesting an involvement of neuroinflammation. More recent investigations have shown evidence for reduced cortical and hippocampal volumes and altered glutamatergic signalling in the WKY strain. Given the growing interest in therapeutics targeting the glutamatergic system, the WKY strain presents itself as a potentially useful tool for screening novel antidepressant drugs and their efficacy against treatment resistant depression. However, despite the sexual dimorphism present in the pathophysiology and aetiology of MDD, sex differences in the WKY model are rarely investigated, with most studies focusing on males. Accordingly, this review highlights what is known regarding sex differences and where further research is needed. Whilst acknowledging that investigation into a range of depression models is required to fully elucidate the underlying mechanisms of MDD, here we review the WKY strain, and its relevance to the clinic.

Long-Term NMDAR Antagonism Correlates Weight Loss With Less Eating

Memantine hydrochloride is an uncompetitive N-methyl-D-aspartate (NMDA) antagonist for treatment of moderate-to-severe Alzheimer's disease. Several studies have shown that memantine can significantly correct the binge-like eating behavior in human and animal models. People with overeating behavior are more likely to be obese. Therefore, we suppose that memantine would be a good candidate for the treatment of obesity. In this study, memantine was shown to increase weight loss in obese mice induced by high fat diet. Memantine was shown to decrease food intake without inducing abdominal discomfort and anxiety, suggesting that this compound would be a good candidate drug for obesity control.

Amelioration of Alzheimer's disease pathology and cognitive deficits by immunomodulatory agents in animal models of Alzheimer's disease

The most common age-related neurodegenerative disease is Alzheimer’s disease (AD) characterized by aggregated amyloid-β (Aβ) peptides in extracellular plaques and aggregated hyperphosphorylated tau protein in intraneuronal neurofibrillary tangles, together with loss of cholinergic neurons, synaptic alterations, and chronic inflammation within the brain. These lead to progressive impairment of cognitive function. There is evidence of innate immune activation in AD with microgliosis. Classically-activated microglia (M1 state) secrete inflammatory and neurotoxic mediators, and peripheral immune cells are recruited to inflammation sites in the brain. The few drugs approved by the US FDA for the treatment of AD improve symptoms but do not change the course of disease progression and may cause some undesirable effects. Translation of active and passive immunotherapy targeting Aβ in AD animal model trials had limited success in clinical trials. Treatment with immunomodulatory/anti-inflammatory agents early in the disease process, while not preventive, is able to inhibit the inflammatory consequences of both Aβ and tau aggregation. The studies described in this review have identified several agents with immunomodulatory properties that alleviated AD pathology and cognitive impairment in animal models of AD. The majority of the animal studies reviewed had used transgenic models of early-onset AD. More effort needs to be given to creat models of late-onset AD. The effects of a combinational therapy involving two or more of the tested pharmaceutical agents, or one of these agents given in conjunction with one of the cell-based therapies, in an aged animal model of AD would warrant investigation.

Combined Memantine and Donepezil Treatment Improves Behavioral and Psychological Symptoms of Dementia-Like Behaviors in Olfactory Bulbectomized Mice

Memantine, an uncompetitive N-methyl-D-aspartate receptor antagonist, and the cholinesterase inhibitor, donepezil, are approved in most countries for treating moderate-to-severe Alzheimer's disease (AD). These drugs have different molecular targets; thus, it is expected that the effects of combined treatment would be synergistic. Some reports do show memantine/donepezil synergy in ameliorating cognition in AD model animals, but their combined effects on behavioral and psychological symptoms of dementia (BPSD)-like behaviors have not been addressed. Here, we investigate combined memantine/donepezil effects on cognitive impairment and BPSD-like behaviors in olfactory bulbectomized (OBX) mice. Interestingly, combined administration synergistically improved both depressive-like behaviors and impaired social interaction in OBX mice, whereas only weak synergistic effects on cognitive performance were seen. To address mechanisms underlying these effects, we used in vivo microdialysis study and observed impaired nicotine-induced serotonin (5-HT) release in OBX mouse hippocampus. Combined memantine/donepezil administration, but not single administration of either, significantly antagonized the decrease in nicotine-induced 5-HT release seen in OBX mouse hippocampus. Furthermore, decreased autophosphorylation of calcium/calmodulin dependent protein kinase II (CaMKII) was rescued in hippocampal CA1 and dentate gyrus of OBX mice by combined memantine/donepezil administration. These results suggest that improvement of BPSD-like behaviors by the co-administration of both drugs is in part mediated by enhanced 5-HT release and CaMKII activity in OBX mouse hippocampus.

Rapamycin blocks the antidepressant effect of ketamine in task-dependent manner

OBJECTIVE

The aim of our study was to test whether ketamine produces an antidepressant effect in animal model of olfactory bulbectomy and assess the role of mammalian target of rapamycin (mTOR) pathway in ketamine's antidepressant effect.

METHODS

Bulbectomized (OBX) rats and sham controls were assigned to four subgroups according to the treatment they received (ketamine, saline, ketamine + rapamycin, and saline + rapamycin). The animals were subjected to open field (OF), elevated plus maze (EPM), passive avoidance (PA), Morris water maze (MWM), and Carousel maze (CM) tests. Blood samples were collected before and after drug administration for analysis of phosphorylated mTOR level. After behavioral testing, brains were removed for evaluation of brain-derived neurotrophic factor (BDNF) in prefrontal cortex (PFC) and hippocampus.

RESULTS

Ketamine normalized hyperactivity of OBX animals in EPM and increased the time spent in open arms. Rapamycin pretreatment resulted in elimination of ketamine effect in EPM test. In CM test, ketamine + rapamycin administration led to cognitive impairment not observed in saline-, ketamine-, or saline + rapamycin-treated OBX rats. Prefrontal BDNF content was significantly decreased, and level of mTOR was significantly elevated in OBX groups.

CONCLUSIONS

OBX animals significantly differed from sham controls in most of the tests used. Treatment had more profound effect on OBX phenotype than controls. Pretreatment with rapamycin eliminated the anxiolytic and antidepressant effects of ketamine in task-dependent manner. The results indicate that ketamine + rapamycin application resulted in impaired stress responses manifested by cognitive deficits in active place avoidance (CM) test. Intensity of stressor (mild vs. severe) used in the behavioral tests had opposite effect on controls and on OBX animals.

Effects of NMDA antagonists on the development and expression of tolerance to diazepam-induced motor impairment in mice

The goal of the study was to investigate the effects of ketamine and memantine on the development and expression of tolerance to diazepam (DZ)-induced motor impairment in mice. DZ-induced motor incoordination was assessed by the rotarod and chimney tests. It was found that (a) ketamine, at the dose of 5mg/kg (but not 2.5mg/kg), decreased the expression, but not the development, of tolerance to the motor impairing effects of DZ, (b) memantine, at the doses of 5 and 10mg/kg decreased both the development and expression of DZ tolerance in the rotarod test (also in the chimney test but at the higher dose of 10mg/kg) and (c) ketamine and memantine alone had no effect, either in the rotarod or the chimney test in mice. Those findings provided behavioral evidence that the glutamatergic system could contribute an important role in the development and/or expression of tolerance to DZ in mice.

Behavior and the cholinergic parameters in olfactory bulbectomized female rodents: Difference between rats and mice

Olfactory bulbectomy (OBX) in rodents induces a wide spectrum of functional disturbances, including behavioral, neurochemical, and neuromorphological alterations. We have examined the effects of OBX on behavior and the parameters of the cholinergic system in female rats and mice. In rats, OBX resulted in the appearance of some depressive-like behavioral marks, such as the decreased sucrose consumption, hyperactivity, impaired short-term memory and anxiety-like behavioral features, such as shortened presence in the center of the open field arena or open arms of the elevated plus-maze and an enhancement of avoidance behavior. These behavioral abnormalities could be associated with disturbances in hippocampal function, this suggestion being supported by the presence of cellular changes in this brain structure. No effect of OBX on the number of cholinergic neurons in the medial septum-diagonal band as well as on the acetylcholine content and acetylcholinesterase activity in the septum, hippocampus, and neocortex could be detected. In contrast, in mice, OBX impaired spontaneous alternation behavior and decreased the number of cholinergic neurons in the medial septum-diagonal band. These data demonstrate that rats and mice differently respond to OBX, in particular, OBX does not significantly affect the cholinergic system in rats.

Thunbergia laurifolia extract ameliorates cognitive and emotional deficits in olfactorectomized mice

CONTEXT

Thunbergia laurifolia Lindl. (Acanthaceae) is a Thai medicinal plant used for the detoxification of poison which is likely to be beneficial for the treatment of cognitive deficits including Alzheimer's disease.

OBJECTIVE

To elucidate the effects of Thunbergia laurifolia leaf extract (TLL) on cognitive dysfunction and depression-like behavior in olfactory bulbectomized mice (OBX).

MATERIALS AND METHODS

OBX mice were treated daily with TLL at the dose of 250 and 500 mg/kg, tacrine, and imipramine, on the day after 10 d of OBX operation. The effects of TLL on cognitive and depression-like behavior of the animals were analyzed. After completing behavioral experiments, the expression levels of cholinergic marker genes encoding ChAT and muscarinic M1 receptor were quantitatively analyzed.

RESULTS

TLL and tacrine reduced OBX-induced cognitive deficits in the object recognition test (ORT) with the time spent for the novel object two times longer than that of the familiar object. Moreover, TLL at the dose of 500 mg/kg and imipramine ameliorated depression-like behavior in the tail suspension test (TST) by reducing the duration of immobility from 25.18% to 3.16% and from 25.18% to 6.48%, respectively. TLL at the dose of 250 and 500 mg/kg reversed the OBX-induced down-regulation of ChAT mRNA expression in the hippocampus from 0.12 to 0.17 and 0.24, respectively, while the down-regulation of mRNA expression of muscarinic M1 receptor was also reversed by TLL from 0.23 to 0.38 and 0.48, respectively.

CONCLUSIONS

TLL ameliorates non-spatial short-term memory deficits in OBX mice, and has the potential to exhibit an antidepressant-like action.

Morinda citrifolia L. (noni) and memantine attenuate periventricular tissue injury of the fourth ventricle in hydrocephalic rabbits

This study was designed to evaluate the neuroprotective effects of Morinda citrifolia L. (Rubiaceae), commonly known as noni, and memantine (a N-methy-D-aspartate receptor inhibitor) on hydrocephalus-induced neurodegenerative disorders. Kaolin was injected into the cistern magna of male adult New Zealand rabbits to establish a hydrocephalus animal model. Memantine (20 mg/kg, intraperitoneally; memantine-treated group) or noni (5 mL/kg, intragastrically; noni-treated group) was administered daily for 2 weeks. Microtubule-associated protein-2 and caspase-3 immunohistochemistry were performed to detect neuronal degeneration and apoptosis in the periventricular tissue of the fourth ventricle of rabbits. Microtubule-associated protein-2 staining density was significantly decreased in the hydrocephalic group, while the staining density was significantly increased in the memantine- and noni-treated groups, especially in the noni-treated group. Noni treatment decreased the number of caspase-3-positive cells in rabbits with hydrocephalus, while memantine had no effect. These findings suggest that noni exhibits more obvious inhibitory effects on hydrocephalus-induced neurodegenerative disorders than memantine in periventricular tissue of the fourth ventricle.

Memantine prevents reference and working memory impairment caused by sleep deprivation in both young and aged Octodon degus

Memory loss is one of the key features of cognitive impairment in either aging, Mild Cognitive Impairment (MCI) or dementia. Pharmacological treatments for memory loss are today focused on addressing symptomatology. One of these approved compounds is memantine, a partial NMDA receptor antagonist that has proved its beneficial effects in cognition. The Octodon degus (O. degus) has been recently proposed as a potential model relevant for neurodegenerative diseases. However, there are no previous studies investigating the effect of pharmacological treatments for age-related cognitive impairment in this rodent. In this work we aimed to evaluate the effect of memantine on sleep deprivation (SD)-induced memory impairment in young and old O. degus. Young and old animals were trained in different behavioral paradigms validated for memory evaluation, and randomly assigned to a control (CTL, n=14) or an SD (n=14) condition, and treated with vehicle or memantine (10-mg/Kg i.p.) before the SD started. We demonstrate that SD impairs memory in both young and old animals, although the effect in the old group was significantly more severe (P<0.05). Memantine pretreatment was able to prevent the cognitive impairment caused by SD in both age groups, while it had no negative effect on CTL animals. The positive effect of memantine in counteracting the negative effect of SD on the retrieval process even in the aged O. degus further supports the translational potential of both the challenge and the species, and will enable a better understanding of the behavioral features of memantine effects, especially related with reference and working memories.

Neuroprotective and cognitive enhancing effects of a multi-targeted food intervention in an animal model of neurodegeneration and depression

Rising neurodegenerative and depressive disease prevalence combined with the lack of effective pharmaceutical treatments and dangerous side effects, has created an urgent need for the development of effective therapies. Considering that these disorders are multifactorial in origin, treatments designed to interfere at different mechanistic levels may be more effective than the traditional single-targeted pharmacological concepts. To that end, an experimental diet composed of zinc, melatonin, curcumin, piperine, eicosapentaenoic acid (EPA, 20:5, n-3), docosahexaenoic acid (DHA, 22:6, n-3), uridine, and choline was formulated. This diet was tested on the olfactory bulbectomized rat (OBX), an established animal model of depression and cognitive decline. The ingredients of the diet have been individually shown to attenuate glutamate excitoxicity, exert potent anti-oxidant/anti-inflammatory properties, and improve synaptogenesis; processes that all have been implicated in neurodegenerative diseases and in the cognitive deficits following OBX in rodents. Dietary treatment started 2 weeks before OBX surgery, continuing for 6 weeks in total. The diet attenuated OBX-induced cognitive and behavioral deficits, except long-term spatial memory. Ameliorating effects of the diet extended to the control animals. Furthermore, the experimental diet reduced hippocampal atrophy and decreased the peripheral immune activation in the OBX rats. The ameliorating effects of the diet on the OBX-induced changes were comparable to those of the NMDA receptor antagonist, memantine, a drug used for the management of Alzheimer's disease. This proof-of-concept study suggests that a diet, which simultaneously targets multiple disease etiologies, can prevent/impede the development of a neurodegenerative and depressive disorders and the concomitant cognitive deficits.

Different effects of the NMDA receptor antagonists ketamine, MK-801, and memantine on postsynaptic density transcripts and their topography: role of Homer signaling, and implications for novel antipsychotic and pro-cognitive targets in psychosis

Administration of NMDA receptor antagonists, such as ketamine and MK-801, may induce psychotic-like behaviors in preclinical models of schizophrenia. Ketamine has also been observed to exacerbate psychotic symptoms in schizophrenia patients. However, memantine, a non-competitive NMDA receptor antagonist approved for Alzheimer's disease and proposed for antipsychotic augmentation, may challenge this view. To date, the molecular mechanisms by which these NMDA receptor antagonists cause different neurochemical, behavioral, and clinical effects are still a matter of debate. Here, we investigated by molecular imaging whether these agents could differently modulate gene expression and topographical distribution of glutamatergic postsynaptic density (PSD) proteins. We focused on Homer1a/Homer1b/PSD-95 signaling network, which may be implicated in glutamate-dependent synaptic plasticity, as well as in psychosis pathophysiology and treatment. Ketamine (25 and 50mg/kg) and MK-801 (0.8mg/kg) significantly induced the transcripts of immediate-early genes (Arc, c-fos, and Homer1a) in cortical regions compared to vehicle, whereas they reduced Homer1b and PSD-95 expression in cortical and striatal regions. Differently, memantine (5mg/kg) did not increase Homer1a signal compared to vehicle, whereas it induced c-fos in the somatosensory and in the medial agranular cortices. Moreover, memantine did not affect Homer1b and PSD-95 expression. When compared to ketamine and MK-801, memantine significantly increased the expression of c-fos, Homer1b and PSD-95. Overall, ketamine and MK-801 prominently increased Homer1a/Homer1b expression ratio, whereas memantine elicited the opposite effect. These data may support the view that ketamine, MK-801 and memantine exert divergent effects on PSD transcripts, which may contribute to their partially different behavioral and clinical effects.

Melancholic microbes: a link between gut microbiota and depression?

There is a growing awareness of the potential for microbiota to influence gut-brain communication in health and disease. A variety of strategies have been used to study the impact of the microbiota on brain function and these include antibiotic use, probiotic treatments, fecal microbiota transplantation, gastrointestinal infection studies, and germ-free studies. All of these approaches provide evidence to support the view that the microbiota can influence brain chemistry and consequently behavior. Efforts are now turning to investigate the role of microbiota in animal models of psychopathology. Animal models of depression are thus essential in studying the complex interplay between the microbiota and brain. Recent studies published in this Journal and elsewhere demonstrate that there is a distinct perturbation of the composition of gut microbiota in animal models of depression and chronic stress. This has direct implications for the development of psychobiotic-based therapeutic strategies for psychiatric disorders. Moreover, given that affective co-morbidities, such as major depression and anxiety states, are common in patients presenting with irritable bowel syndrome (IBS), it may have implications for functional bowel disorders also. Further studies require appropriately phenotyped patients with depression and/or IBS using a judicious use of techniques including functional imaging and in depth microbial pyrosequencing.