Non-competitive NMDAR Antagonist Research Articles

Design, Synthesis, and Study of Novel Memantine Schiff Base Derivatives Against Targeted Enzymes in Alzheimer’s Disease

Introduction: According to WHO, Alzheimer’s disease was estimated at 74.4 million cases in 2023, which will increase by 152.8 million cases in 2050. The therapeutic options available in the market for the treatment of AD are only capable of reducing the symptoms of dementia but not preventing progressive degeneration. Memantine is a non-competitive NMDAR antagonist used for the treatment of patients with moderate-to-severe AD, but it has a high toxicity profile. To counter this, the Memantine Schiff base derivatives were designed as simple and lowtoxicity compounds. Materials and Methods: Molecular docking was performed against the targeted enzymes Acetylcholinesterase and Butyrylcholinesterase using AUTODOCK 1.5.7 software. A series of novel Memantine derivatives of Schiff base were synthesized by condensing Memantine with various aryl aldehydes and screened for their invitro-cholinesterase inhibitory activity towards Acetylcholinesterase (AChE) and Butyrylcholinesterase (BChE) by Ellman’s method. Results and Discussion: Among the designed compounds, compounds LMV and LMC showed maximum binding scores of -10.35 kcal/mol and -10.12 kcal/mol, respectively, than the standard Donepezil (-8.78 kcal/mol) against Acetylcholinesterase. The compounds LMONB and LMDMB produced significant binding scores of -9.31 kcal/mol and -9.11 kcal/mol, respectively, compared to the standard Donepezil (-7.57 kcal/mol) against Butyrylcholinesterase. Also, compounds LMV (30.9 ± 2.13 μM) and LMDMB (13.51 ± 1.12 μM) showed potent inhibitory activity against the AChE and BChE. These compounds possess drug-like characteristics and are also capable of crossing the Blood Brain Barrier (BBB). Conclusion: The studied compounds LMV and LMDMB, being non-toxic, obey Lipinski’s rule of 5 and are potential inhibitors against targeted enzymes, which may be promising clinical candidates for treating Alzheimer’s disease.

Two distinct enriched housings differentially ameliorate object and place recognition deficits in a rat model of schizophrenia

Schizophrenia is a psychiatric disorder characterized by cognitive dysfunctions. These dysfunctions significantly impact the daily lives of schizophrenic patients, yet effective interventions remain scarce. In this study, we explored the effects of two enriched housing types—cognitive and physical—on cognitive dysfunctions in a rat model of schizophrenia. Male neonatal Wistar-Imamichi rats were administered MK-801, a noncompetitive NMDAR antagonist, twice daily from postnatal day (PND) 7 to PND 20. Physical enrichment ameliorated memory deficits in both object and place recognition tests, while cognitive enrichment primarily improved object recognition performance. Our findings suggest that exercise therapy could be a potential approach to address cognitive dysfunctions in schizophrenia patients.

Unraveling the Interplay of 5-hydroxytryptamine-3 and N-methyl-d-aspartate Receptors in Seizure Susceptibility

Abstract Background Epilepsy, a prevalent neurological disorder characterized by recurrent seizures, presents significant challenges in treatment and management. This study aimed to evaluate the effect of tropisetron, a selective 5-HT3 receptor antagonist on pentylenetetrazole (PTZ) – induced seizure in mice by exploring the potential role of the NMDA receptor and inflammatory responses. Methods For this purpose, seizures were induced by intravenous PTZ infusion. Tropisetron at 1-, 2-, 3-, 5-, 10- mg/kg were administered intraperitoneally 30 minutes before PTZ. To evaluate probable role of NMDA signaling, selective NMDAR antagonists, ketamine and MK-801, were injected 15 minutes before tropisetron. Also, TNF-α level of hippocampus were measured following administration of mentioned drugs in mice. Results Our results demonstrate that tropisetron displayed a dose-dependent impact on seizure threshold, with certain doses (5 and 10 mg/kg) exhibiting anticonvulsant properties. In addition, the noncompetitive NMDAR antagonists, ketamine (1 mg/kg) and MK-801 (0.5 mg/kg), at doses that had no effect on seizure threshold, augmented the anticonvulsant effect of tropisetron (3 mg/kg). Also, tropisetron led to a reduction in hippocampal TNF-α levels, indicating its anti-inflammatory potential independent of 5-HT receptor activity. Conclusion In conclusion, we demonstrated that the anticonvulsant effect of tropisetron is mediated by the inhibition of NMDA receptors and a decline in hippocampal TNF-α level. These findings highlight a potential connection between 5-HT3 and NMDA receptors in the pharmacological treatment of inflammatory diseases, such as seizure, warranting further investigation into their combined therapeutic effects.

Chronic memantine disrupts spatial memory and up-regulates Htr1a gene expression in the hippocampus of GPR39 (zinc-sensing receptor) KO male mice

GPR39 is a receptor involved in zincergic neurotransmission, and its role in regulating psychological functions is an active area of research. The purported roles of GPR39 at the cellular level include regulation of inflammatory and oxidative stress response, and modulation of GABAergic and endocannabinoid neurotransmission. GPR39 knock-out (KO) mice exhibit episodic-like and spatial memory (ELM and SM, respectively) deficits throughout their lifetime, and are similar in that respect to senescent wild-type (WT) conspecifics. Since a role for zinc has been postulated in neurodegenerative disorders, in this study we investigated the possibility of a pharmacological rescue of both types of declarative memory with memantine - a noncompetitive NMDAR antagonist used for slowing down dementia; or, a putative GPR39 agonist – TC-G 1008.First, we tested adult WT and GPR39KO male mice under acute 5 mg/kg memantine or vehicle treatment in an object recognition task designed to simultaneously probe the “what?”, “where?” and “when?” components of ELM. Next, we investigated the impact of chronic memantine or TC-G 1008 on ELM and SM (Morris water maze, MWM) in both WT and GPR39KO mice. Following chronic experiments, we assessed with qRT-PCR hippocampal gene expression of targets previously associated with GPR39.We report: no effects of acute memantine on ELM; a tendency to improve the “where?” component of ELM in both WT and GPR39 KO mice following 12 days of memantine; and, a disruption of SM in GPR39KO mice after 24 days of memantine treatment. The latter result was associated with upregulation of Htr1a hippocampal expression.

Effectiveness and Tolerability of Intranasal Esketamine in Treatment-Resistant Depression: Report of Two Clinical Cases

IntroductionMajor depressive disorder (MDD) is a mental health disorder characterised by persistently low mood; anhedonia; feelings of worthlessness and guilt; altered appetite, weight and sleep and suicidal ideation. About one-third of patients do not respond to available antidepressants (AD). Treatment-resistant depression (TRD) is a clinical term used to define a lack of response to two or more AD in patients with MDD that do not respond to other lines of treatment either. TRD is associated with an increased risk of relapse, hospitalisation and suicide. Esketamine is a non-competitive NMDAR antagonist that acts as an antidepressant by modulating glutamatergic neurotransmission, disturbed in MDD patients. It has recently been approved by the European Commission as a fast-acting nasal spray therapy for depression and suicidal ideation after showing effectiveness in TRD patients (Papakostas et al. JCP 2020; 81 4).ObjectivesThe aim of this study is to determine the effectiveness, safety and tolerability of intranasal esketamine in two TRD-diagnosed patients and to assess their clinical evolution.MethodsA prospective study was conducted describing the evolution of two TRD patients treated with intranasal esketamine. We used The Hamilton Depression Rating Scale (HDRS) to quantify the severity of their symptoms and assess their recovery over time, analyzing the score change from baseline to endpoint as a primary outcome of the study. We also applied the Addensbrooke Cognitive Examination (ACE-III) as a tool to establish their cognitive condition before therapy and its evolution. Changes in dosage during treatment, adverse effects, time required for onset of action, clinical outcomes and other variables were also measured.ResultsIntranasal esketamine was administered twice a week during the first 4-week induction phase and weekly during the following 6-month maintenance phase. Dosage of antidepressant was determined depending on each patient’s age and clinical evolution, being 56 mg the initial dose for case 1 (57 years old) and 28 mg for case 2 (71 years old). This antidepressant was effective in both patients in a fast-acting way, with the onset of action occuring within the first two weeks. During the course of treatment, the HDRS score significantly decreased, associated with improvement and remission of depressive symptoms. Cognitive performance got better in both cases. None of the patients discontinued treatment due to adverse effects or lack of efficacy.ConclusionsOur data suggest that intranasal esketamine therapy is a good alternative in TRD patients, being effective, fast-acting and well-tolerated, with a manageable safety profile. Clinical stability was also observed in the medium-term follow-up after the end of treatment. This presents esketamine as a promising therapeutic and effective strategy in MDD patients who are either treatment-resistant or acutely suicidal.Disclosure of InterestNone Declared

Promises and Pitfalls of NMDA Receptor Antagonists in Treating Violent Aggression

Treatment options for chronically aggressive individuals remain limited despite recent medical advances. Traditional pharmacological agents used to treat aggression, such as atypical antipsychotics, have limited efficacy and are often replete with dangerous side effects. The non-competitive NMDAR antagonists ketamine and memantine are promising alternatives, but their effects appear to be highly dependent on dosage, context, and personal experience. Importantly, these drugs can increase aggression when combined with substances of abuse or during periods of heightened stress. This is likely due to mechanistic differences operating at specific synapses under different contexts. Previous findings from our lab and others have shown that early life stress, substance abuse, and attack experience promote aggression through NMDAR-dependent synaptic plasticity within aggression-related brain circuits. Ketamine and memantine affect these types of aggression in opposite ways. This has led us to propose that ketamine and memantine oppositely affect aggression brought on by early life stress, substance abuse, or attack experience through opposite effects on NMDAR-dependent synaptic plasticity. This would account for the persistent effects of these drugs on aggression and suggest they could be leveraged as a more long-lasting treatment option. However, a more thorough examination of the effects of ketamine and memantine on cellular and synaptic function will be necessary for responsible administration. Additionally, because the effects of ketamine and memantine are highly dependent on prior drug use, traumatic stress, or a history of aggressive behavior, we propose a more thorough medical evaluation and psychiatric assessment will be necessary to avoid possible adverse interactions with these drugs.

Characterization of a differential reinforcement of low rates of responding task in non-deprived male and female rats: Role of Sigma-1 receptors

Impulsive action can be defined as the inability to withhold a response and represents one of the dimensions of the broad construct impulsivity. Here, we characterized a modified differential reinforcement of low rates of responding (DRL) task developed in our laboratory, in which impulsive action is measured in ad libitum fed/watered subjects. Specifically, we first determined the effects of both sex and estrous cycle on impulsive action by systematically comparing male and estrous-synchronized female subjects. In addition, we evaluated the convergent validity of this modified DRL task by testing the effects of the D2R/5HT2AR antagonist, aripiprazole, and the noncompetitive NMDAR antagonist, MK-801. Finally, we tested the effects of the selective antagonist BD-1063 and agonist PRE-084 of Sigma-1 receptor (Sig-1R) on impulsive action using this modified DRL task. We found that female rats showed and increased inability to withhold a response when compared to males, and this effect was driven by the metestrus/diestrus phase of the estrous cycle. In addition, aripiprazole and MK-801 fully retained their capability to reduce and increase impulsive action, respectively. Finally, the selective Sig-1R antagonist, BD-1063 dose-dependently reduced the inability to withhold a response in both sexes, though more potently in female rats. In summary, we show that impulsive action, as measured in a modified DRL task which minimizes energy-homeostatic influences, is a function of both sex and estrous cycle. Furthermore, we validate the convergent validity of the task and provide evidence that Sig-1R antagonism may represent a novel pharmacological strategy to reduce impulsive action.

Subanesthetic ketamine rapidly alters medial prefrontal miRNAs involved in ubiquitin-mediated proteolysis.

Ketamine is a dissociative anesthetic and a non-competitive NMDAR antagonist. At subanesthetic dose, ketamine can relieve pain and work as a fast-acting antidepressant, but the underlying molecular mechanism remains elusive. This study aimed to investigate the mode of action underlying the effects of acute subanesthetic ketamine treatment by bioinformatics analyses of miRNAs in the medial prefrontal cortex of male C57BL/6J mice. Gene Ontology and KEGG pathway analyses of the genes putatively targeted by ketamine-responsive prefrontal miRNAs revealed that acute subanesthetic ketamine modifies ubiquitin-mediated proteolysis. Validation analysis suggested that miR-148a-3p and miR-128-3p are the main players responsible for the subanesthetic ketamine-mediated alteration of ubiquitin-mediated proteolysis through varied regulation of ubiquitin ligases E2 and E3. Collectively, our data imply that the prefrontal miRNA-dependent modulation of ubiquitin-mediated proteolysis is at least partially involved in the mode of action by acute subanesthetic ketamine treatment.

Involvement of NMDA receptors containing the GluN2C subunit in the psychotomimetic and antidepressant-like effects of ketamine

Acute ketamine administration evokes rapid and sustained antidepressant effects in treatment-resistant patients. However, ketamine also produces transient perceptual disturbances similarly to those evoked by other non-competitive NMDA-R antagonists like phencyclidine (PCP). Although the brain networks involved in both ketamine actions are not fully understood, PCP and ketamine activate thalamo-cortical networks after NMDA-R blockade in GABAergic neurons of the reticular thalamic nucleus (RtN). Given the involvement of thalamo-cortical networks in processing sensory information, these networks may underlie psychotomimetic action. Since the GluN2C subunit is densely expressed in the thalamus, including the RtN, we examined the dependence of psychotomimetic and antidepressant-like actions of ketamine on the presence of GluN2C subunits, using wild-type and GluN2C knockout (GluN2CKO) mice. Likewise, since few studies have investigated ketamine’s effects in females, we used mice of both sexes. GluN2C deletion dramatically reduced stereotyped (circling) behavior induced by ketamine in male and female mice, while the antidepressant-like effect was fully preserved in both genotypes and sexes. Despite ketamine appeared to induce similar effects in both sexes, some neurobiological differences were observed between male and female mice regarding c-fos expression in thalamic nuclei and cerebellum, and glutamate surge in prefrontal cortex. In conclusion, the GluN2C subunit may discriminate between antidepressant-like and psychotomimetic actions of ketamine. Further, the abundant presence of GluN2C subunits in the cerebellum and the improved motor coordination of GluN2CKO mice after ketamine treatment suggest the involvement of cerebellar NMDA-Rs in some behavioral actions of ketamine.

Ketamine activated glutamatergic neurotransmission by GABAergic disinhibition in the medial prefrontal cortex

The fast-onset antidepressant actions of ketamine at subanaesthetic doses have attracted enormous interest in psychiatric disease treatment. However, the severe psychotomimetic side effects foster an urgent need to deeply understand the fast-onset antidepressant mechanism of ketamine. Ketamine, as a non-competitive NMDAR antagonist, increases the overall excitability of the mPFC, which is presumed to be essential for the antidepressant action of ketamine. However, the underlying mechanism is still elusive. Here, our results showed that low concentration of ketamine increased the activity and the excitatory/inhibitory ratio of pyramidal neurons; these changes were accompanied by diminished interneurons activity in the mPFC. Moreover, ketamine induced increases in excitatory transmission and antidepressant-like effects, which might rely on the functional intact of GABAergic system in the mPFC. These results suggest a critical role of the mPFC GABAergic system in the fast antidepressant effects of a subanaesthetic dose ketamine.

Amantadine Combines Astroglial System Xc- Activation with Glutamate/NMDA Receptor Inhibition.

A glutamate/NMDA receptor (NMDA-R) antagonist, amantadine (AMA) exhibits a broad spectrum of clinically important properties, including antiviral, antiparkinsonian, neuroprotective, neuro-reparative and cognitive-enhancing effects. However, both clinical and pre-clinical studies have demonstrated that noncompetitive NMDA-R antagonists induce severe schizophrenia-like cognitive deficits. Therefore, this study aims to clarify the clinical discrepancy between AMA and noncompetitive NMDA-R antagonists by comparing the effects of AMA with those of a noncompetitive NMDA-R antagonist, MK801, on rat tripartite glutamatergic synaptic transmission using microdialysis and primary cultured astrocytes. Microdialysis study demonstrated that the stimulatory effects of AMA on L-glutamate release differed from those of MK801 in the globus pallidus, entorhinal cortex and entopeduncular nucleus. The stimulatory effect of AMA on L-glutamate release was modulated by activation of cystine/glutamate antiporter (Sxc). Primary cultured astrocytes study demonstrated that AMA also enhanced glutathione synthesis via Sxc activation. Furthermore, carbon-monoxide induced damage of the astroglial glutathione synthesis system was repaired by AMA but not MK801. Additionally, glutamate/AMPA receptor (AMPA-R) antagonist, perampanel enhanced the protective effects of AMA. The findings of microdialysis and cultured astrocyte studies suggest that a combination of Sxc activation with inhibitions of ionotropic glutamate receptors contributes to neuroprotective, neuro-reparative and cognitive-enhancing activities that can mitigate several neuropsychiatric disorders.

Neuropharmacological Screening of Chiral and Non-chiral Phthalimide- Containing Compounds in Mice: in vivo and in silico Experiments.

Thalidomide, the first synthesized phthalimide, has demonstrated sedative- hypnotic and antiepileptic effects on the central nervous system. N-substituted phthalimides have an interesting chemical structure that confers important biological properties. Non-chiral (ortho and para bis-isoindoline-1,3-dione, phthaloylglycine) and chiral phthalimides (N-substituted with aspartate or glutamate) were synthesized and the sedative, anxiolytic and anticonvulsant effects were tested. Homology modeling and molecular docking were employed to predict recognition of the analogues by hNMDA and mGlu receptors. The neuropharmacological activity was tested with the open field test and elevated plus maze (EPM). The compounds were tested in mouse models of acute convulsions induced either by pentylenetetrazol (PTZ; 90 mg/kg) or 4-aminopyridine (4-AP; 10 mg/kg). The ortho and para non-chiral compounds at 562.3 and 316 mg/kg, respectively, decreased locomotor activity. Contrarily, the chiral compounds produced excitatory effects. Increased locomotor activity was found with S-TGLU and R-TGLU at 100, 316 and 562.3 mg/kg, and S-TASP at 316 and 562.3 mg/kg. These molecules showed no activity in the EPM test or PTZ model. In the 4-AP model, however, S-TGLU (237.1, 316 and 421.7 mg/kg) as well as S-TASP and R-TASP (316 mg/kg) lowered the convulsive and death rate. The chiral compounds exhibited a non-competitive NMDAR antagonist profile and the non-chiral molecules possessed selective sedative properties. The NMDAR exhibited stereoselectivity for S-TGLU while it is not a preference for the aspartic derivatives. The results appear to be supported by the in silico studies, which evidenced a high affinity of phthalimides for the hNMDAR and mGluR type 1.

Buspirone Counteracts MK-801-Induced Schizophrenia-Like Phenotypes through Dopamine D3 Receptor Blockade.

Background: Several efforts have been made to develop effective antipsychotic drugs. Currently, available antipsychotics are effective on positive symptoms, less on negative symptoms, but not on cognitive impairment, a clinically relevant dimension of schizophrenia. Drug repurposing offers great advantages over the long-lasting, risky and expensive, de novo drug discovery strategy. To our knowledge, the possible antipsychotic properties of buspirone, an azapirone anxiolytic drug marketed in 1986 as serotonin 5-HT1A receptor (5-HT1AR) partial agonist, have not been extensively investigated despite its intriguing pharmacodynamic profile, which includes dopamine D3 (D3R) and D4 receptor (D4R) antagonist activity. Multiple lines of evidence point to D3R as a valid therapeutic target for the treatment of several neuropsychiatric disorders including schizophrenia. In the present study, we tested the hypothesis that buspirone, behaving as dopamine D3R antagonist, may have antipsychotic-like activity.Materials and Methods: Effects of acute administration of buspirone was assessed on a wide-range of schizophrenia-relevant abnormalities induced by a single administration of the non-competitive NMDAR antagonist MK-801, in both wild-type mice (WT) and D3R-null mutant mice (D3R-/-).Results: Buspirone (3 mg⋅kg-1, i.p.) was devoid of cataleptogenic activity in itself, but resulted effective in counteracting disruption of prepulse inhibition (PPI), hyperlocomotion and deficit of temporal order recognition memory (TOR) induced by MK-801 (0.1 mg⋅kg-1, i.p.) in WT mice. Conversely, in D3R-/- mice, buspirone was ineffective in preventing MK-801-induced TOR deficit and it was only partially effective in blocking MK-801-stimulated hyperlocomotion.Conclusion: Taken together, these results indicate, for the first time, that buspirone, might be a potential therapeutic medication for the treatment of schizophrenia. In particular, buspirone, through its D3R antagonist activity, may be a useful tool for improving the treatment of cognitive deficits in schizophrenia that still represents an unmet need of this disease.

Acute systemic MK-801 induced functional uncoupling between hippocampal areas CA3 and CA1 with distant effect in the retrosplenial cortex

The hippocampus and retrosplenial cortex are integrated within a higher-order cognitive circuit supporting relational (spatial, contextual, episodic) forms of learning and memory. Hippocampal place cells can coordinate multiple parallel representations in the same physical environment. Novel environment exploration triggers expression of immediate-early genes (IEGs) Arc and Homer1a in spatial context-specific ensembles of CA1 and CA3 neurons. Less is know about ensemble coding in the retrosplenial cortex (RSC), a region directly connected and functionally coupled to CA1. Hippocampal and retrosplenial damage is found in patients with schizophrenia alongside cognitive deficits affecting relational memory. Systemic administration of non-competitive NMDAR antagonists such as MK-801 is used to model psychosis in animals and humans. Acute systemic MK-801 (0.15 mg/kg) impaired cognitive control in rats and ensemble code for spatial context in CA1. Here, we use expression of immediate-early genes Arc and Homer 1a to examine ensemble coding in rat CA3 and RSC to test if the effect of MK-801 extends upstream and downstream of CA1, respectively. Different rats explored the same context twice (A/A), explored two distinct contexts (A/B) or remained in their home cage (CC). In contrast to CA1, MK-801 did not affect ensemble coding in CA3. Unlike CA3 and CA1, similarity of RSC ensembles active during exploration did not reflect change in spatial context, but MK-801 (0.15 mg/kg) increased similarity in RSC ensembles active during spontaneous behavior in the home cage. The data provide support for MK-801-induced functional uncoupling between CA3 and CA1 and suggest that ensemble coding deficit may extend downstream of CA1. This deficit may reflect hyperassociative state in the cognitive circuit underlying cognitive disorganization in psychosis. © 2016 Wiley Periodicals, Inc.

NMDA receptor antagonist prevents cell death in the hippocampal dentate gyrus induced by hyponatremia accompanying adrenal insufficiency in rats

Selective apoptosis of granule cells in the hippocampal dentate gyrus (DG) of rats with bilateral adrenalectomy (ADX) and in patients who died of adrenal insufficiency has been reported. Although adrenal insufficiency is a common disease and is usually associated with hyponatremia, its effect on the central nervous system and in apoptosis in the hippocampus remain to be elucidated. Using rat models to represent clinical hyponatremia accompanying adrenal insufficiency, we show that reduced serum [Na+] was associated with selective apoptosis in the DG. Nine days after ADX, apoptotic cells were observed in the DG of rats whose serum [Na+] was <125mEq/L (moderate hyponatremia), but rarely in those whose serum [Na+] was ≥125mEq/L or in normonatremic rats. Although all hyponatremic ADX rats survived following treatment with corticosterone and saline started 7days after ADX when apoptosis had not yet occurred, selective apoptosis on day 9 was not prevented in moderately hyponatremic rats. Interestingly, treatment with memantine, a noncompetitive NMDAR antagonist, prevented the selective apoptosis in the DG in moderately hyponatremic, ADX rats, and improved electrophysiological dysfunction, including impaired basal synaptic transmission and long-term potentiation at the entorhinal cortex-DG synapses. These results demonstrated that in adrenal insufficient rats, hyponatremia was associated with apoptosis in the DG, and that memantine prevented the apoptosis and improved cell function. Our data imply the importance of assessing the possibility of neurological impairments after treatment with CORT in patients with moderate or severe hyponatremia accompanying adrenal insufficiency and that memantine may represent a beneficial therapeutic strategy to prevent neurological impairments in such patients.

The serotonergic hallucinogen 5-methoxy-N,N-dimethyltryptamine disrupts cortical activity in a regionally-selective manner via 5-HT1A and 5-HT2A receptors

5-Methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is a natural hallucinogen, acting as a non-selective serotonin 5-HT1A/5-HT2A-R agonist. Psychotomimetic agents such as the non-competitive NMDA-R antagonist phencyclidine and serotonergic hallucinogens (DOI and 5-MeO-DMT) disrupt cortical synchrony in the low frequency range (<4 Hz) in rat prefrontal cortex (PFC), an effect reversed by antipsychotic drugs. Here we extend these observations by examining the effect of 5-MeO-DMT on low frequency cortical oscillations (LFCO, <4 Hz) in PFC, visual (V1), somatosensory (S1) and auditory (Au1) cortices, as well as the dependence of these effects on 5-HT1A-R and 5-HT2A-R, using wild type (WT) and 5-HT2A-R knockout (KO2A) anesthetized mice. 5-MeO-DMT reduced LFCO in the PFC of WT and KO2A mice. The effect in KO2A mice was fully prevented by the 5-HT1A-R antagonist WAY-100635. Systemic and local 5-MeO-DMT reduced 5-HT release in PFC mainly via 5-HT1A-R. Moreover, 5-MeO-DMT reduced LFCO in S1, Au1 and V1 of WT mice and only in V1 of KO2A mice, suggesting the involvement of 5-HT1A-R activation in the 5-MeO-DMT-induced disruption of V1 activity. In addition, antipsychotic drugs reversed 5-MeO-DMT effects in WT mice. The present results suggest that the hallucinogen action of 5-MeO-DMT is mediated by simultaneous alterations of the activity of sensory (S1, Au1, V1) and associative (PFC) cortical areas, also supporting a role of 5-HT1A-R stimulation in V1 and PFC, in addition to the well-known action on 5-HT2A-R. Moreover, the reversal by antipsychotic drugs of 5-MeO-DMT effects adds to previous literature supporting the usefulness of the present model in antipsychotic drug development.

Strain-dependent effects on acquisition and reversal of visual and spatial tasks in a rat touchscreen battery of cognition

AimThe use of touch-screen equipped operant boxes is an increasingly popular method for modeling human cognition in the rodent. A concern of this approach is that the dependence upon vision may limit the strains of rats that can be tested in the apparatus. This is of particular concern because of the increased availability of genetically modified rats that are disproportionately on an albino background and may have compromised vision. Here we test pigmented and albino strains of rats on three touch-screen tasks of learning and memory that may require different levels of visual ability. In tests where albino animals have similar levels of performance as the pigmented rats we also tested common pharmacological models of cognitive impairment to determine the generalizability of these challenges across strains. By doing this work we hope to determine the robustness of common models of pharmacological impairment in albino rats. MethodsWe tested four strains of rats (albino: Wistar and Sprague Dawley, pigmented: Long Evans and Lister Hooded) in three touchscreen-based tasks of cognition with differing visual requirements: visual discrimination (VD) acquisition and reversal learning, and the more spatial and less visually demanding, automated spatial search task (AST). Furthermore, we tested the effects of the muscarinic antagonist scopolamine and the non-competitive NMDAR antagonist MK801 on performance of the four strains in AST. Finally, visual acuity was also assessed via a movement detection test. ResultsThe rate of acquisition (% correct) in albino rats was significantly slower than in pigmented rats. Wistar rats were significantly slower to acquire the task, and showed differences in reversal learning when compared to the pigmented strains. Moreover, SD rats performed so badly during the acquisition phase of the VD that they failed to reach inclusion criteria (80% correct responses over 3-sessions) for the reversal phase. In contrast, no effect of strain was found in AST. Some of these differences can likely be attributed to differences in visual acuity as albino animals appeared to have reduced visual acuity when compared to the pigmented animals as previously reported in the literature. Pharmacological challenge with scopolamine or MK801 induced dissociable effects between compounds, but generally comparable impairments in all four strains. ConclusionsAlbino animals showed a clear impairment on tasks that are dependent upon intact vision, while no impairment was observed in the visually less demanding spatial task. Despite a published report to the contrary, these results demonstrate that albino strains may not be appropriate for use in touchscreen tasks that are dependent upon a visual discrimination. Furthermore, the spatial search task showed distinct impairment profiles as a result of treatment with either MK-801 or scopolamine. While an interaction did exist between strain and treatment, the dissociation between MK-801 and scopolamine was consistent across 3 of 4 strains. These results highlight the importance of selecting the appropriate strain for use in tasks of visual learning and memory and also demonstrate the potential robustness of pharmacological models of cognitive impairment across strains.

NMDA-receptor antagonists block B-cell function but foster IL-10 production in BCR/CD40-activated B cells.

BackgroundB cells are important effectors and regulators of adaptive and innate immune responses, inflammation and autoimmunity, for instance in anti-NMDA-receptor (NMDAR) encephalitis. Thus, pharmacological modulation of B-cell function could be an effective regimen in therapeutic strategies. Since the non-competitive NMDAR antagonist memantine is clinically applied to treat advanced Alzheimer`s disease and ketamine is supposed to improve the course of resistant depression, it is important to know how these drugs affect B-cell function.ResultsNon-competitive NMDAR antagonists impaired B-cell receptor (BCR)- and lipopolysaccharide (LPS)-induced B-cell proliferation, reduced B-cell migration towards the chemokines SDF-1α and CCL21 and downregulated IgM and IgG secretion. Mechanistically, these effects were mediated through a blockade of Kv1.3 and KCa3.1 potassium channels and resulted in an attenuated Ca2+-flux and activation of Erk1/2, Akt and NFATc1. Interestingly, NMDAR antagonist treatment increased the frequency of IL-10 producing B cells after BCR/CD40 stimulation.ConclusionsNon-competitive NMDAR antagonists attenuate BCR and Toll-like receptor 4 (TLR4) B-cell signaling and effector function and can foster IL-10 production. Consequently, NMDAR antagonists may be useful to target B cells in autoimmune diseases or pathological systemic inflammation. The drugs’ additional side effects on B cells should be considered in treatments of neuronal disorders with NMDAR antagonists.

The reduction of nNOS and ROS associated with decreased Ca2+ in hippocampus of prenatally stressed female offspring

Prenatal stress (PS) has been known to induce oxidative damage in the offspring hippocampus. Previous researches observe that the alterations of expression of nNOS, ROS and intracellular Ca2+ in the hippocampus are advanced in the prenatally stressed female offspring rats. The objective of this study was to explore whether MK-801, a non-competitive NMDAR antagonist, could have protective effect on the oxidative stress induced by PS. Pregnant rats were randomly divided into four groups: CON group; PS group; PS+NS group; PS+MK-801 group. Eight female offspring rats were used in each group in the present experiment. Prenatally stressed rats (PS group; PS+NS group; PS+MK-801 group) exposed to restraint stress from day 14 to 20 of gestation three times daily for 45 min every time. We assayed the expression of nNOS with immunohistochemistry, ROS production with fluorescent dye Fluo3-AM dye. To measure whether intracellular Ca2+ was involved in the changes of nNOS and ROS, we also assayed the concentration of intracellular Ca2+ with DCFH-DA. Our findings showed that MK-801 lowered the increase of the nNOS expression in the hippocampus subregions and ROS in the CA3 region of female offspring, which may be relevant to the decreasing concentration of intracellular Ca2+. These results suggest that MK-801 may be associated with the protective effect on oxidative stress induced by PS.

Effects of rhynchophylline on GluN1 and GluN2B expressions in primary cultured hippocampal neurons

N-methyl-d-aspartate (NMDA) receptor subunits GluN1 and GluN2B in hippocampal neurons play key roles in anxiety. Our previous studies show that rhynchophylline, an active component of the Uncaria species, down-regulates GluN2B expression in the hippocampal CA1 area of amphetamine-induced rat. The effects of rhynchophylline on expressions of GluN1 and GluN2B in primary hippocampal neurons in neonatal rats in vitro were investigated. Neonatal hippocampal neurons were cultured with neurobasal-A medium. After incubation for 6h or 48h with rhynchophylline (non-competitive NMDAR antagonist) and MK-801 (non-competitive NMDAR antagonist with anxiolytic effect, as the control drug) from day6, neuron toxicity, mRNA and protein expressions of GluN1 and GluN2B were analyzed. GluN1 is mainly distributed on neuronal axons and dendritic trunks, cytoplasm and cell membrane near axons and dendrites. GluN2B is mainly distributed on the membrane, dendrites, and axon membranes. GluN1 and GluN2B are codistributed on dendritic trunks and dendritic spines. After 48h incubation, a lower concentration of rhynchophylline (lower than 400μmol/L) and MK-801 (lower than 200μmol/L) have no toxicity on neonatal hippocampal neurons. Rhynchophylline up-regulated GluN1 mRNA expression at 6h and mRNA and protein expressions at 48h, but down-regulated GluN2B mRNA and protein expressions at 48h. However, GluN1 and GluN2B mRNA expressions were down-regulated at 6h, and mRNA and protein expressions were both up-regulated by MK-801 at 48h. These findings show that rhynchophylline reciprocally regulates GluN1 and GluN2B expressions in hippocampal neurons, indicating a potential anxiolytic property for rhynchophylline.