Memantine Effects on Electroencephalographic Measures of Putative Excitatory/Inhibitory Balance in Schizophrenia

BACKGROUND

Abnormalities in cortical excitation and inhibition (E/I) balance are thought to underlie sensory and information processing deficits in schizophrenia. Deficits in early auditory information processing mediate both neurocognitive and functional impairment and appear to be normalized by acute pharmacologic challenge with the NMDA antagonist memantine (MEM).

METHODS

Thirty-six subjects with a diagnosis of schizophrenia and 31 healthy control subjects underwent electroencephalographic recordings. Subjects ingested either placebo or MEM (10 or 20 mg) in a double-blind, within-subject, crossover, randomized design. The aperiodic, 1/f-like scaling property of the neural power spectra, which is thought to index relative E/I balance, was estimated using a robust linear regression algorithm.

RESULTS

Patients with schizophrenia had greater aperiodic components compared with healthy control subjects (p < .01, d = 0.64), which was normalized after 20 mg MEM. Analysis revealed a significant dose × diagnosis interaction (p < .0001, d = 0.82). Furthermore, the MEM effect (change in aperiodic component in MEM vs. placebo conditions) was associated with baseline attention and vigilance (r = .54, p < .05) and MEM-induced enhancements in gamma power (r = -.60, p < .01).

CONCLUSIONS

Findings confirmed E/I balance abnormalities in schizophrenia that were normalized with acute MEM administration and suggest that neurocognitive profiles may predict treatment response based on E/I sensitivity. These data provide proof-of-concept evidence for the utility of E/I balance indices as metrics of acute pharmacologic sensitivity for central nervous system therapeutics.

Memantine protects thalamocortical hyper-glutamatergic transmission induced by NMDA receptor antagonism via activation of system xc<sup/>

Deficiencies in N-methyl-d-aspartate (NMDA)/glutamate receptor (NMDAR) signaling have been considered central to the cognitive impairments of schizophrenia; however, an NMDAR antagonist memantine (MEM) improves cognitive impairments of Alzheimer's disease and schizophrenia. These mechanisms of paradoxical clinical effects of NMDAR antagonists remain unclear. To explore the mechanisms by which MK801 and MEM affect thalamocortical transmission, we determined interactions between local administrations of MK801, MEM, system xc^- (Sxc), and metabotropic glutamate receptors (mGluRs) on extracellular glutamate and GABA levels in the mediodorsal thalamic nucleus (MDTN) and medial prefrontal cortex (mPFC) using dual-probe microdialysis with ultra-high-pressure liquid chromatography. Effects of MK801 and MEM on Sxc activity were also determined using primary cultured astrocytes. Sxc activity was enhanced by MEM, but was unaffected by MK801. MK801 enhanced thalamocortical glutamatergic transmission by GABAergic disinhibition in the MDTN. In the MDTN and the mPFC, MEM weakly increased glutamate release by activating Sxc, whereas MEM inhibited thalamocortical glutamatergic transmission. Paradoxical effects of MEM were induced following secondary activation of inhibitory II-mGluR and III-mGluR by exporting glutamate from astroglial Sxc. The present results suggest that the effects of therapeutically relevant concentrations of MEM on thalamocortical glutamatergic transmission are predominantly caused by activation of Sxc rather than inhibition of NMDAR. These demonstrations suggest that the combination between reduced NMDAR and activated Sxc contribute to the neuroprotective effects of MEM. Furthermore, activation of Sxc may compensate for the cognitive impairments that are induced by hyperactivation of thalamocortical glutamatergic transmission following activation of Sxc/II-mGluR in the MDTN and Sxc/II-mGluR/III-mGluR in the mPFC.

The role of memantine in the treatment of major depressive disorder: Clinical efficacy and mechanisms of action

A developing body of evidence indicates that disturbed glutamate neurotransmission especially through N-methyl-d-aspartate (NMDA) is central to the pathophysiology of major depressive disorder (MDD) and NMDA receptor antagonists have shown therapeutic potential in the MDD treatment. Memantine is an uncompetitive NMDA receptor antagonist, approved for treatment of Alzheimer's disease (AD) that in contrast to other NMDA receptor antagonists at therapeutic doses does not induce highly undesirable side effects. Neuroprotective properties and well tolerability of memantine have been attributed to its unique pharmacological features such as moderate affinity, rapid blocking kinetics and strongly voltage-dependency. In this review we summarized clinical trial evidence of antidepressant effectiveness of memantine and its mechanisms of action. Available data indicate contradictory findings relating to clinical efficacy suggesting further research is necessary in determining as to whether memantine will eventually be an advantageous therapy for MDD. Preclinical data proposed various neurobiological mechanisms underlying antidepressant-like properties of memantine that are responsible for synaptic plasticity and cell survival.

Effect of co-administration of memantine and sertraline on the antidepressant-like activity and brain-derived neurotrophic factor (BDNF) levels in the rat brain

A developing body of data has drawn attention to the N-methyl-d-aspartate (NMDA) receptor antagonists as potential drugs for the treatment of major depressive disorder (MDD). We investigated the possibility of synergistic interactions between the antidepressant sertraline with the uncompetitive NMDA receptor antagonist, memantine. The present study was aimed to evaluate behavioural and molecular effects of the chronic treatment with memantine and sertraline alone or in combination in rats. To this aim, rats were chronically treated with memantine (2.5 and 5mg/kg) and sertraline (5mg/kg) for 14days once a day, and then exposed to the forced swimming test. The brain-derived neurotrophic factor (BDNF) levels were assessed in the hippocampus and prefrontal cortex in all groups by ELISA sandwich assay. Sertraline and memantine (2.5mg/kg) alone did not have effect on the immobility time; however, the effect of sertraline was enhanced by both doses of memantine. Combined treatment with memantine and sertraline produced stronger increases in the BDNF protein levels in the hippocampus and prefrontal cortex. Our results indicate that co-administration of antidepressant memantine with sertraline may induce a more pronounced antidepressant activity than treatment with each antidepressant alone. Antidepressant properties using the combination of memantine and sertraline could be attributed to increased levels of BDNF. This finding may be of particular importance in the case of drug-resistant patients and could suggest a method of obtaining significant antidepressant actions whereas limiting side effects.

Aggression and increased glutamate in the mPFC during withdrawal from intermittent alcohol in outbred mice

RATIONALE

Disrupted social behavior, including occasional aggressive outbursts, is characteristic of withdrawal from long-term alcohol (EtOH) use. Heavy EtOH use and exaggerated responses during withdrawal may be treated using glutamatergic N-methyl-D-aspartate receptor (NMDAR) antagonists.

OBJECTIVES

The current experiments explore aggression and medial prefrontal cortex (mPFC) glutamate as consequences of withdrawal from intermittent access to EtOH and changes in aggression and mPFC glutamate caused by NMDAR antagonists memantine and ketamine.

METHODS

Swiss male mice underwent withdrawal following 1-8 weeks of intermittent access to 20 % EtOH. Aggressive and nonaggressive behaviors with a conspecific were measured 6-8 h into EtOH withdrawal after memantine or ketamine (0-30 mg/kg, i.p.) administration. In separate mice, extracellular mPFC glutamate after memantine was measured during withdrawal using in vivo microdialysis.

RESULTS

At 6-8 h withdrawal from EtOH, mice exhibited more convulsions and aggression and decreased social contact compared to age-matched water controls. Memantine, but not ketamine, increased withdrawal aggression at the 5-mg/kg dose in mice with a history of 8 weeks of EtOH but not 1 or 4 weeks of EtOH or in water drinkers. Tonic mPFC glutamate was higher during withdrawal after 8 weeks of EtOH compared to 1 week of EtOH or 8 weeks of water. Five milligrams per kilogram of memantine increased glutamate in 8-week EtOH mice, but also in 1-week EtOH and water drinkers.

CONCLUSIONS

These studies reveal aggressive behavior as a novel symptom of EtOH withdrawal in outbred mice and confirm a role of NMDARs during withdrawal aggression and for disrupted social behavior.

Dinitrobenzene sulphonic acid-induced colitis impairs spatial recognition memory in mice: roles of N-methyl D-aspartate receptors and nitric oxide

RATIONALE

Many peripheral diseases are associated with a decline in cognitive function. In this regard, there have been reports of patients with inflammatory bowel disease and an otherwise unexplained memory impairment.

OBJECTIVES

We sought to assess the memory performance of mice with colitis. We also investigated the roles of N-methyl D-aspartate (NMDA) receptors and nitric oxide (NO) as possible mediators of colitis-induced amnesia.

METHODS

To induce colitis, male NMRI mice were intrarectally injected with a solution containing dinitrobenzene sulfonic acid (DNBS; 4 mg in 100 μl) under anesthesia. Three days after intrarectal DNBS instillation, spatial recognition and associative memories were assessed by the Y-maze and passive avoidance tasks, respectively. The NMDA antagonists, MK-801 and memantine, and the inducible NO synthase (iNOS) inhibitor, aminoguanidine, were injected intraperitoneally 45 min before the Y-maze task.

RESULTS

Induction of colitis by DNBS impaired spatial recognition memory in the Y-maze task but had no effect on step through latencies in the passive avoidance test. Colitis-induced amnesia was reversed by administering specific doses of MK-801 and memantine (30 μg/kg and 1 mg/kg, respectively) suggesting dysregulated NMDA receptor activation as an underlying mechanism. No effect was seen with lower and higher doses of these drugs, resulting in a bell-shaped dose response curve. Colitis-induced amnesia was also inhibited by aminoguanidine (50 mg/kg), implicating a role for iNOS activation and neuroinflammation in this phenomenon.

CONCLUSION

DNBS-induced colitis impairs memory through NMDA receptor overstimulation and NO overproduction.

Predicting targets of compounds against neurological diseases using cheminformatic methodology

Recently developed multi-targeted ligands are novel drug candidates able to interact with monoamine oxidase A and B; acetylcholinesterase and butyrylcholinesterase; or with histamine N-methyltransferase and histamine H3-receptor (H3R). These proteins are drug targets in the treatment of depression, Alzheimer's disease, obsessive disorders, and Parkinson's disease. A probabilistic method, the Parzen-Rosenblatt window approach, was used to build a "predictor" model using data collected from the ChEMBL database. The model can be used to predict both the primary pharmaceutical target and off-targets of a compound based on its structure. Molecular structures were represented based on the circular fingerprint methodology. The same approach was used to build a "predictor" model from the DrugBank dataset to determine the main pharmacological groups of the compound. The study of off-target interactions is now recognised as crucial to the understanding of both drug action and toxicology. Primary pharmaceutical targets and off-targets for the novel multi-target ligands were examined by use of the developed cheminformatic method. Several multi-target ligands were selected for further study, as compounds with possible additional beneficial pharmacological activities. The cheminformatic targets identifications were in agreement with four 3D-QSAR (H3R/D1R/D2R/5-HT2aR) models and by in vitro assays for serotonin 5-HT1a and 5-HT2a receptor binding of the most promising ligand (71/MBA-VEG8).

AlzPlatform: an Alzheimer's disease domain-specific chemogenomics knowledgebase for polypharmacology and target identification research

Alzheimer’s disease (AD) is one of the most complicated progressive neurodegeneration diseases that involve many genes, proteins, and their complex interactions. No effective medicines or treatments are available yet to stop or reverse the progression of the disease due to its polygenic nature. To facilitate discovery of new AD drugs and better understand the AD neurosignaling pathways involved, we have constructed an Alzheimer’s disease domain-specific chemogenomics knowledgebase, AlzPlatform (www.cbligand.org/AD/) with cloud computing and sourcing functions. AlzPlatform is implemented with powerful computational algorithms, including our established TargetHunter, HTDocking, and BBB Predictor for target identification and polypharmacology analysis for AD research. The platform has assembled various AD-related chemogenomics data records, including 928 genes and 320 proteins related to AD, 194 AD drugs approved or in clinical trials, and 405 188 chemicals associated with 1 023 137 records of reported bioactivities from 38 284 corresponding bioassays and 10 050 references. Furthermore, we have demonstrated the application of the AlzPlatform in three case studies for identification of multitargets and polypharmacology analysis of FDA-approved drugs and also for screening and prediction of new AD active small chemical molecules and potential novel AD drug targets by our established TargetHunter and/or HTDocking programs. The predictions were confirmed by reported bioactivity data and our in vitro experimental validation. Overall, AlzPlatform will enrich our knowledge for AD target identification, drug discovery, and polypharmacology analyses and, also, facilitate the chemogenomics data sharing and information exchange/communications in aid of new anti-AD drug discovery and development.

Memantine may affect pseudobulbar affect in patients with Alzheimer's disease

OBJECTIVE

Behavioural symptoms are common in moderate to severe Alzheimer's disease (AD) and are improved by memantine with the most pronounced effect on agitation/aggression. Dextromethorphan in combination with quinidine is the only drug approved by US Food and Drug Administration for the treatment of pseudobulbar affect (PBA) on the basis of efficacy in patients with multiple sclerosis or amyotrophic lateral sclerosis. The aim of our study was to evaluate the efficacy of memantine on PBA in patients with AD.

METHODS

In a prospective, double-blind, case-control study to assess PBA with pathological laughter and crying scale patients were administered memantine (final dose of 20 mg daily) or citalopram (20 mg once daily), each for 10 weeks. The number of episodes of involuntary emotional expression, Neuropsychiatric Inventory (NPI) and Overt Aggression Scale-Modified (OAS-M) total scores were also recorded. Furthermore, the platelet serotonin (5-HT) concentration was measured.

RESULTS

Although memantine had beneficial effects on PBA, it also had a crucial impact on behavioural symptoms, especially aggression and agitation (to an average of 3.5 times higher end-point scores on OAS-M and increase of NPI total scores for an average of 114% of initial value). Therefore, the study was prematurely stopped. In addition, we had evidenced a drop of platelet 5-HT concentration (to an average of 73% of initial value).

CONCLUSION

Surprisingly, our research showed the opposite action of memantine on neuropsychiatric symptoms as expected. In a limited number of AD patients with PBA, memantine had a beneficial effect on involuntary emotional expression, but it potentiated agitation/aggression, irritability and caused a crucial drop of the platelet 5-HT concentration.

Anti-dyskinetic mechanisms of amantadine and dextromethorphan in the 6-OHDA rat model of Parkinson's disease: role of NMDA vs. 5-HT1A receptors

Amantadine and dextromethorphan suppress levodopa (L-DOPA)-induced dyskinesia (LID) in patients with Parkinson's disease (PD) and abnormal involuntary movements (AIMs) in the unilateral 6-hydroxydopamine (6-OHDA) rat model. These effects have been attributed to N-methyl-d-aspartate (NMDA) antagonism. However, amantadine and dextromethorphan are also thought to block serotonin (5-HT) uptake and cause 5-HT overflow, leading to stimulation of 5-HT(1A) receptors, which has been shown to reduce LID. We undertook a study in 6-OHDA rats to determine whether the anti-dyskinetic effects of these two compounds are mediated by NMDA antagonism and/or 5-HT(1A) agonism. In addition, we assessed the sensorimotor effects of these drugs using the Vibrissae-Stimulated Forelimb Placement and Cylinder tests. Our data show that the AIM-suppressing effect of amantadine was not affected by the 5-HT(1A) antagonist WAY-100635, but was partially reversed by the NMDA agonist d-cycloserine. Conversely, the AIM-suppressing effect of dextromethorphan was prevented by WAY-100635 but not by d-cycloserine. Neither amantadine nor dextromethorphan affected the therapeutic effects of L-DOPA in sensorimotor tests. We conclude that the anti-dyskinetic effect of amantadine is partially dependent on NMDA antagonism, while dextromethorphan suppresses AIMs via indirect 5-HT(1A) agonism. Combined with previous work from our group, our results support the investigation of 5-HT(1A) agonists as pharmacotherapies for LID in PD patients.

Cell proliferation in the hippocampus and in the heart is modified by exposure to repeated stress and treatment with memantine

The present studies were aimed to verify the hypothesis that treatment with memantine, a low affinity NMDA glutamate receptor antagonist, can reduce possible stress-induced alterations in cell proliferation in the hippocampus and in the heart and has consequences on stress hormone release. Adult male Wistar rats were exposed to repeated hypokinesis (movement restraint, 2 h daily) or remained undisturbed and they were treated with memantine (5 mg/kg/day, s.c.) or vehicle for 8 days. On the day 7, all animals were injected with 5-bromo-2'-deoxyuridine (BrdU), a marker of cell proliferation. The mild form of chronic stress used resulted only in moderate decrease in BrdU incorporation into DNA in the hippocampus, while the same stimulus caused a pronounced reduction of the new cells formed in left heart ventricle. In both tissues, stress-induced reduction in cell proliferation was more evident in memantine-treated rats. Memantine failed to modify hormones of the hypothalamic-pituitary-adrenocortical axis, while the treatment increased plasma renin activity. The present study demonstrates that treatment with memantine potentiated rather than prevented stress-induced reduction of cell proliferation. We have shown that stress exposure may induce a reduction in cell proliferation in the heart, even in a higher extent than that in the hippocampus. Effects of memantine under stress conditions might be relevant with respect to clinical use of memantine, which is being used in the treatment of neurodegenerative diseases.

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

Memantine, a non-competitive NMDA receptor antagonist, is used for the treatment of Alzheimer's disease (AD) and off-label as an anti-depressant. Here we investigated possible anti-depressant, cognitive enhancing and neuroprotective effects of memantine in the olfactory bulbectomized (OBX) rat. OBX is used as a screening model for antidepressants and shows cognitive disturbances. In Experiment I, memantine treatment started 14 days after OBX surgery (this setup is similar to what we use for screening of potential antidepressants) and 2 days before surgery in experiment II. In both experiments, memantine (20 mg/kg, p.o) was administered once daily for 28 days. Animals were tested in the open field (locomotor activity), passive avoidance (fear learning and memory), and holeboard (spatial acquisition and memory) before and after the bulbectomy. Memantine, when administered before surgery, prevented OBX-induced hyperactivity and partly fear memory loss. These behavioral effects were present for at least 3 weeks after cessation of treatment. Memantine, however did not improve spatial memory. When administered 2 weeks after OBX surgery, memantine was ineffective in normalizing open field hyperactivity and improving cognitive deficits. Interestingly, after the animals were retrained in passive avoidance, memantine- treated OBX rats (both in experiment I and II) showed improved fear learning and memory. Our findings suggest that memantine has both neuroprotective and cognitive enhancing effects without antidepressant-like properties in the OBX rat. Based on our results, we propose that memantine may be more beneficial to AD patients when administered early in the disease process.

Open-label study of the short-term effects of memantine on FDG-PET in frontotemporal dementia

BACKGROUND

Memantine has shown effects on cortical metabolism in Alzheimer's disease (AD), and the mechanism of action may not be specific to AD alone. We hypothesized that participants with frontotemporal dementia taking memantine would show an increased cortical metabolic activity in frontal regions, temporal regions, or in salience network hubs.

METHODS

Sixteen participants with behavioral or language variant frontotemporal dementia syndromes (FTD) were recruited from tertiary FTD clinics and treated with memantine hydrochloride 10 mg twice daily in this fixed-dose, open-label pilot study. The primary endpoint was enhancement of cortical metabolic activity after 7-8 weeks of treatment. Secondary endpoints were measures of mood and behavior disturbance, frontal executive function, and motor disturbance.

RESULTS

Voxel-wise parametric image analysis of positron emission tomography (PET) data from seven behavioral variant FTD patients, eight semantic dementia patients, and one progressive nonfluent aphasia patient, of mean age 64.3 years, mean duration of illness 4.25 years, and baseline mean sum of boxes Clinical Dementia Rating score 6.59, revealed an increase in [(18)F]-fluorodeoxyglucose (FDG) normalized metabolic activity in bilateral insulae and the left orbitofrontal cortex (P < 0.01). The increase on FDG-PET did not correlate with changes on behavioral inventories. Post hoc analysis indicated that semantic dementia participants drove this finding.

CONCLUSION

This open-label clinical PET study suggests that memantine induces an increase in metabolism in the salience network in FTD. A placebo-controlled follow-up study is warranted.

Neurochemical changes in a double transgenic mouse model of Alzheimer's disease fed a pro-oxidant diet

Oxidative stress is implicated in the pathogenesis of Alzheimer's disease (AD) causing neurodegeneration and decreased monoamine neurotransmitters. We investigated the effect of administration of a pro-oxidant diet on the levels of monoamines and metabolites in the brains of wildtype and transgenic mice expressing mutant APP and PS-1 (TASTPM mice). Three-month-old TASTPM and wildtype (C57BL6/J) mice were fed either normal or pro-oxidant diet for 3 months. The neocortex, cerebellum, hippocampus and striatum were assayed for their monoamine and monoamine metabolite content using HPLC with electrochemical detection. Striatal tyrosine hydroxylase (TOH) levels were analysed by Western blotting. In the striatum, female TASTPM mice had higher levels of DOPAC and male TASTPM mice had higher levels of 5-HIAA compared to wildtype mice. Administration of pro-oxidant diet increased striatal MHPG, turnover of NA and 5-HT levels in female TASTPM mice compared to TASTPM mice fed control diet. The pro-oxidant diet also decreased DOPAC levels in female TASTPM mice compared to those fed control diet. Striatal TOH did not depend on diet, gender or genotype. In the neocortex, the TASTPM genotype increased levels of 5-HIAA in male mice fed control diet compared to wildtype mice. In the cerebellum, the TASTPM genotype led to decreased levels of HVA (male mice only) and also decreased turnover of DA (female mice only) compared to wildtype mice. These data suggest a sparing of monoaminergic neurones in the cortex, striatum and hippocampus of TASTPM mice fed pro-oxidant diet and could be indicative of increased activity in corticostriatal circuits. The decreased cerebellar levels of HVA and turnover of DA in TASTPM mice hint at possible axonal degeneration within this subregion.

Effects of long-term memantine on memory and neuropathology in Ts65Dn mice, a model for Down syndrome

Memantine is a partial NMDA receptor antagonist that has been shown to improve learning and memory in several animal models, and is approved for the treatment of Alzheimer's disease (AD). Chronic treatments using memantine in animal models of Alzheimer's disease show disease-modifying effects and suggest a potential neuroprotective function. The present study assessed the effects of both short- and long-term memantine treatment in a mouse model of Down syndrome (DS), the Ts65Dn mouse. The Ts65Dn mouse contains a partial trisomy of murine chromosome 16, and exhibits hippocampal-dependent memory deficits, as well as progressive degeneration of basal forebrain cholinergic neurons (BCFNs). Ts65Dn mice were treated with memantine for a period of 6 months, beginning at 4 months of age. At the end of treatment the mice underwent memory testing using novel object recognition and water radial arm maze tasks, and then histologically analyzed for markers of neurodegeneration. Memantine treatment improved spatial and recognition memory performance in the Ts65Dn mice, though not to the level of normosomic littermate controls. Despite these memory improvements, histological analysis found no morphological signs of neuroprotection of basal forebrain cholinergic or locus coeruleus neurons in memantine-treated Ts65Dn mice. However, memantine treatment of Ts65Dn mice gave rise to elevated brain-derived neurotrophic factor expression in the hippocampus and frontal cortex, suggesting a mechanism of behavioral modification. Thus, our findings provide further evidence for memory facilitation of memantine, but suggest pharmacological rather than neuroprotective effects of memantine both after acute and chronic treatment in this mouse model.

Neurochemical and behavioural effects of acute and chronic memantine administration in rats: Further support for NMDA as a new pharmacological target for the treatment of depression?

A growing body of evidence has pointed to the NMDA receptor antagonists as a potential therapeutic target for the treatment of major depression. The present study was aimed to evaluate behavioural and molecular effects of the acute and chronic treatment with memantine and imipramine in rats. To this aim, rats were acutely or chronically for 14 days once a day treated with memantine (5, 10 and 20 mg/kg) and imipramine (10, 20 and 30 mg/kg) and then subjected to the forced swimming and open-field tests. The acute treatment with memantine at all doses and imipramine at doses (20 and 30 mg/kg) reduced immobility time of rats compared to the saline group (p < 0.05), without affecting spontaneous locomotor activity and chronic treatment with memantine and imipramine, at all doses tested, reduced immobility time of rats compared to the saline group (p < 0.05), without affecting spontaneous locomotor activity. Brain-derived neurotrophic factor (BDNF) hippocampal levels were assessed in imipramine- and memantine-treated rats by ELISA sandwich assay. Interesting enough, acute administration, but not chronic administration of memantine at higher dose (20 mg/kg) increased BDNF protein levels in the rat hippocampus (p < 0.05). Finally, these findings further support the hypothesis that NMDA receptor could be a new pharmacological target for the treatment of depression.