Memantine alters striatal plasticity inducing a shift of synaptic responses toward long-term depression

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.

G protein-coupled receptors in neurodegenerative diseases and psychiatric disorders

Neuropsychiatric disorders are multifactorial disorders with diverse aetiological factors. Identifying treatment targets is challenging because the diseases are resulting from heterogeneous biological, genetic, and environmental factors. Nevertheless, the increasing understanding of G protein-coupled receptor (GPCR) opens a new possibility in drug discovery. Harnessing our knowledge of molecular mechanisms and structural information of GPCRs will be advantageous for developing effective drugs. This review provides an overview of the role of GPCRs in various neurodegenerative and psychiatric diseases. Besides, we highlight the emerging opportunities of novel GPCR targets and address recent progress in GPCR drug development.

A Novel Based-Network Strategy to Identify Phytochemicals from Radix Salviae Miltiorrhizae (Danshen) for Treating Alzheimer's Disease

Alzheimer’s disease (AD) is a common age-related neurodegenerative disease that strikes millions worldwide. Herein, we demonstrate a new approach based on network target to identify anti-AD compounds from Danshen. Network pharmacology and molecular docking were employed to establish the DS-AD network, which mainly involved apoptosis of neuron cells. Then network scoring was confirmed via Connectivity Map analysis. M308 (Danshenxinkun D) was an anti-AD candidate with a high score (p < 0.01). Furthermore, we conducted ex vivo experiments with H2O2-treated PC12 cells to verify the neuroprotective effect of Salvia miltiorrhiza-containing plasma (SMP), and UPLC-Q-TOF/MS and RT-qPCR were performed to demonstrate the anti-AD activity of M308 from SMP. Results revealed that SMP could enhance cell viability and level of acetylcholine. AO/EB staining and Mitochondrial membrane potential (MMP) analysis showed that SMP significantly suppressed apoptosis, which may be due to anti-oxidative stress activity. Moreover, the effects of M308 and SMP on expressions of PSEN1, DRD2, and APP mRNA were consistent, and M308 can significantly reverse the expression of PSEN1 and DRD2 mRNA in H2O2-treated PC12 cells. The strategy based on the network could be employed to identify anti-AD compounds from Chinese herbs. Notably, M308 stands out as a promising anti-AD candidate for development.

Memantine treatment does not affect compulsive behavior or frontostriatal connectivity in an adolescent rat model for quinpirole-induced compulsive checking behavior

RATIONALE

Compulsivity often develops during childhood and is associated with elevated glutamate levels within the frontostriatal system. This suggests that anti-glutamatergic drugs, like memantine, may be an effective treatment.

OBJECTIVE

Our goal was to characterize the acute and chronic effect of memantine treatment on compulsive behavior and frontostriatal network structure and function in an adolescent rat model of compulsivity.

METHODS

Juvenile Sprague-Dawley rats received repeated quinpirole, resulting in compulsive checking behavior (n = 32; compulsive) or saline injections (n = 32; control). Eight compulsive and control rats received chronic memantine treatment, and eight compulsive and control rats received saline treatment for seven consecutive days between the 10th and 12th quinpirole/saline injection. Compulsive checking behavior was assessed, and structural and functional brain connectivity was measured with diffusion MRI and resting-state fMRI before and after treatment. The other rats received an acute single memantine (compulsive: n = 12; control: n = 12) or saline injection (compulsive: n = 4; control: n = 4) during pharmacological MRI after the 12th quinpirole/saline injection. An additional group of rats received a single memantine injection after a single quinpirole injection (n = 8).

RESULTS

Memantine treatment did not affect compulsive checking nor frontostriatal structural and functional connectivity in the quinpirole-induced adolescent rat model. While memantine activated the frontal cortex in control rats, no significant activation responses were measured after single or repeated quinpirole injections.

CONCLUSIONS

The lack of a memantine treatment effect in quinpirole-induced compulsive adolescent rats may be partly explained by the interaction between glutamatergic and dopaminergic receptors in the brain, which can be evaluated with functional MRI.

Oleamide Induces Cell Death in Glioblastoma RG2 Cells by a Cannabinoid Receptor-Independent Mechanism

The endocannabinoid system has been associated with antiproliferative effects in several types of tumors through cannabinoid receptor-mediated cell death mechanisms. Oleamide (ODA) is a CB1/CB2 agonist associated with cell growth and migration by adhesion and/or ionic signals associated with Gap junctions. Antiproliferative mechanisms related to ODA remain unknown. In this work, we evaluated the effects of ODA on cell viability and morphological changes in a rat RG2 glioblastoma cell line and compared these effects with primary astrocyte cultures from 8-day postnatal rats. RG2 and primary astrocyte cultures were treated with ODA at increasing concentrations (25, 50, 100, and 200 μM) for different periods of time (12, 24, and 48 h). Changes in RG2 cell viability and morphology induced by ODA were assessed by viability/mitochondrial activity test and phase contrast microscopy, respectively. The ratios of necrotic and apoptotic cell death, and cell cycle alterations, were evaluated by flow cytometry. The roles of CB1 and CB2 receptors on ODA-induced changes were explored with specific receptor antagonists. ODA (100 μM) induced somatic damage, detachment of somatic bodies, cytoplasmic polarization, and somatic shrinkage in RG2 cells at 24 and 48 h. In contrast, primary astrocytes treated at the same ODA concentrations exhibited cell aggregation but not cell damage. ODA (100 μM) increased apoptotic cell death and cell arrest in the G1 phase at 24 h in the RG2 line. The effects induced by ODA on cell viability of RG2 cells were independent of CB1 and CB2 receptors or changes in intracellular calcium transient. Results of this novel study suggest that ODA exerts specific antiproliferative effects on RG2 glioblastoma cells through unconventional apoptotic mechanisms not involving canonical signals.

Interactive effects of age and recent substance use on striatal shape morphology at substance use disorder treatment entry

BACKGROUND

Striatal neuroadaptations are regarded to play an important role in the progression from voluntary to compulsive use of addictive substances and provide a promising target for the identification of neuroimaging biomarkers. Recent advances in surface-based computational analysis enable morphological assessment linking variations in global and local striatal shape to duration and magnitude of substance use with a degree of sensitivity that exceeds standard volumetric analysis.

METHODS

This study used a new segmentation methodology coupled with local surface-based indices of surface area and displacement to provide a comprehensive structural characterization of the striatum in 34 patients entering treatment for substance use disorder (SUD) and 49 controls, and to examine the influence of recent substance use on abnormal age-related striatal deformation in SUD patients.

RESULTS

Patients showed a small reduction in striatal volume and no difference in surface area or shape in comparison to controls. Between-group differences in shape were likely neutralized by the bidirectional influence of recent substance use on striatal shape in SUD patients. Specifically, there was an interaction between age and substance such that among older patients more drug use was associated with greater inward striatal contraction but more alcohol use was associated with greater outward expansion.

CONCLUSIONS

This study builds on previous work and advances our understanding of the nature of striatal neuroadaptations as a potential biomarker of disease progression in addiction.

N-methyl-d-aspartate-type glutamate receptor modulators and related medications for the enhancement of auditory system plasticity in schizophrenia

Deficits in N-methyl-d-aspartate-type (NMDAR) function contribute to cognitive deficits in schizophrenia, particularly dysfunction in neuroplasticity, defined as reduced learning during training on exercises that place implicit, increasing demands on early sensory (auditory and visual) information processing. Auditory mismatch negativity (MMN) can be both a target engagement biomarker for the NMDAR and a proxy measure of neurophysiological plasticity. This review covers the evidence for using NMDAR modulator and related compounds for enhancement of cognition, with a particular focus on early auditory processing/plasticity. Compounds covered include glycine site agonists, glycine and system A-type transporter inhibitors, d-amino acid oxidase inhibitors, memantine and nicotinic alpha-7 acetylcholine receptor agonists. As opposed to daily treatment studies focusing on schizophrenia in general, intermittent, non-daily treatment combining NMDAR modulators with neuroplasticity-based paradigms, using MMN as target-engagement biomarkers show promise as treatments to both remediate plasticity deficits and overall functional deficits.

Auditory System Target Engagement During Plasticity-Based Interventions in Schizophrenia: A Focus on Modulation of N-Methyl-D-Aspartate-Type Glutamate Receptor Function

Cognitive deficits are predictive of long-term social and occupational functional deficits in schizophrenia but are currently without gold-standard treatments. In particular, augmentation of auditory cortical neuroplasticity may represent a rate-limiting first step before addressing higher-order cognitive deficits. We review the rationale for N-methyl-d-aspartate-type glutamate receptor (NMDAR) modulators as treatments for auditory plasticity deficits in schizophrenia, along with potential serum and electroencephalographic target engagement biomarkers for NMDAR function. Several recently published NMDAR-modulating treatment studies are covered, involving D-serine, memantine, and transcranial direct current stimulation. While all three interventions appear to modulate auditory plasticity, direct agonists (D-serine) appear to have the largest and most consistent effects on plasticity, at least acutely. We hypothesize that there may be synergistic effects of combining procognitive NMDAR-modulating approaches with auditory cortical neuroplasticity cognitive training interventions. Future studies should assess biomarkers for target engagement and patient stratification, along with head-to-head studies comparing putative interventions and potential long-term versus acute effects.

Amantadine Did Not Positively Impact Cognition in Chronic Traumatic Brain Injury: A Multi-Site, Randomized, Controlled Trial

Despite limited evidence to support the use of amantadine to enhance cognitive function after traumatic brain injury (TBI), the clinical use for this purpose is highly prevalent and is often based on inferred belief systems. The aim of this study was to assess effect of amantadine on cognition among individuals with a history of TBI and behavioral disturbance using a parallel-group, randomized, double-blind, placebo-controlled trial of amantadine 100 mg twice-daily versus placebo for 60 days. Included in the study were 119 individuals with two or more neuropsychological measures greater than 1 standard deviation below normative means from a larger study of 168 individuals with chronic TBI (>6 months post-injury) and irritability. Cognitive function was measured at treatment days 0, 28, and 60 with a battery of neuropsychological tests. Composite indices were generated: General Cognitive Index (included all measures), a Learning Memory Index (learning/memory measures), and Attention/Processing Speed Index (attention and executive function measures). Repeated-measures analysis of variance revealed statistically significant between-group differences favoring the placebo group at day 28 for General Cognitive Index (p = 0.002) and Learning Memory Index (p = 0.001), but not Attention/Processing Speed Index (p = 0.25), whereas no statistically significant between-group differences were found at day 60. There were no statistically significant between-group differences on adverse events. Cognitive function in individuals with chronic TBI is not improved by amantadine 100 mg twice-daily. In the first 28 days of use, amantadine may impede cognitive processing. However, the effect size was small and mean scores for both groups were generally within expectations for persons with history of complicated mild-to-severe TBI, suggesting that changes observed across assessments may not have functional significance. The use of amantadine to enhance cognitive function is not supported by these findings.

Bidirectional and long-lasting control of alcohol-seeking behavior by corticostriatal LTP and LTD

Addiction is proposed to arise from alterations in synaptic strength via mechanisms of long-term potentiation (LTP) and depression (LTD). However, the causality between these synaptic processes and addictive behaviors is difficult to demonstrate. Here we report that LTP and LTD induction altered operant alcohol self-administration, a motivated drug-seeking behavior. We first induced LTP by pairing presynaptic glutamatergic stimulation with optogenetic postsynaptic depolarization in the dorsomedial striatum, a brain region known to control goal-directed behavior. Blockade of this LTP by NMDA-receptor inhibition unmasked an endocannabinoid-dependent LTD. In vivo application of the LTP-inducing protocol caused a long-lasting increase in alcohol-seeking behavior, while the LTD protocol decreased this behavior. We further identified that optogenetic LTP and LTD induction at cortical inputs onto striatal dopamine D1 receptor-expressing neurons controlled these behavioral changes. Our results demonstrate a causal link between synaptic plasticity and alcohol-seeking behavior and suggest that modulation of this plasticity may inspire a therapeutic strategy for addiction.

Allicin attenuates tunicamycin-induced cognitive deficits in rats via its synaptic plasticity regulatory activity

Objective(s):

To illuminate the functional effects of allicin on rats with cognitive deficits induced by tunicamycin (TM) and the molecular mechanism of this process.

Materials and Methods:

200–250 g male SD rats were divided into three groups at random: control group (n=12), TM group (5 μl, 50 μM, ICV, n=12), and allicin treatment group (180 mg/kg/d with chow diet, n=12). After 16 weeks of allicin treatment, the learning ability and memory were tested using novel object recognition (NOR) testing on rats with 72 hr TM treatment (5 μl, 50 μM, ICV); meanwhile, the variation of field excitatory postsynaptic potential (fEPSP) in the Schaffer Collateral (SC)-CA1 synapse was detected by extracellular electrophysiological recordings and the morphology of dendritic spine was observed by Golgi staining as well as detecting several synaptic plasticity-related proteins by Western blot.

Results:

The density of dendritic spine was increased significantly in allicin-treated groups and the correspondence slope of fEPSP in TM-induced cognitive deficits group was enhanced and expression of synaptophysin and glutamate receptor-1(GluR1) in hippocampal neurons was up-regulated.

Conclusion:

The results indicate that allicin plays an important role in synaptic plasticity regulation. These finding showed that allicin could be used as a pharmacologic treatment in TM-induced cognitive deficits.

Memantine improves outcomes after repetitive traumatic brain injury

Repetitive mild traumatic brain injury (rmTBI; e.g., sports concussions) is common and results in significant cognitive impairment. Targeted therapies for rmTBI are lacking, though evidence from other injury models indicates that targeting N-methyl-d-aspartate (NMDA) receptor (NMDAR)-mediated glutamatergic toxicity might mitigate rmTBI-induced neurologic deficits. However, there is a paucity of preclinical or clinical data regarding NMDAR antagonist efficacy in the rmTBI setting. To test whether NMDAR antagonist therapy improves outcomes after rmTBI, mice were subjected to rmTBI injury (4 injuries in 4days) and randomized to treatment with the NMDA antagonist memantine or with vehicle. Functional outcomes were assessed by motor, anxiety/impulsivity and mnemonic behavioral tests. At the synaptic level, NMDAR-dependent long-term potentiation (LTP) was assessed in isolated neocortical slices. At the molecular level, the magnitude of gliosis and tau hyper-phosphorylation was tested by Western blot and immunostaining, and NMDAR subunit expression was evaluated by Western blot and polymerase chain reaction (PCR). Compared to vehicle-treated mice, memantine-treated mice had reduced tau phosphorylation at acute time points after injury, and less glial activation and LTP deficit 1 month after injury. Treatment with memantine also corresponded to normal NMDAR expression after rmTBI. No corresponding protection in behavior outcomes was observed. Here we found NMDAR antagonist therapy may improve histopathological and functional outcomes after rmTBI, though without consistent corresponding improvement in behavioral outcomes. These data raise prospects for therapeutic post-concussive NMDAR antagonism, particularly in athletes and warriors, who suffer functional impairment and neurodegenerative sequelae after multiple concussions.

Recent trends in the transdermal delivery of therapeutic agents used for the management of neurodegenerative diseases

With the increasing proportion of the global geriatric population, it becomes obvious that neurodegenerative diseases will become more widespread. From an epidemiological standpoint, it is necessary to develop new therapeutic agents for the management of Alzheimer's disease, Parkinson's disease, multiple sclerosis and other neurodegenerative disorders. An important approach in this regard involves the use of the transdermal route. With transdermal drug delivery systems (TDDS), it is possible to modulate the pharmacokinetic profiles of these medications and improve patient compliance. Transdermal drug delivery has also been shown to be useful for drugs with short half-life and low or unpredictable bioavailability. In this review, several transdermal drug delivery enhancement technologies are being discussed in relation to the delivery of medications used for the management of neurodegenerative disorders.