Non-competitive Antagonist Research Articles

Effectiveness and safety of Perampanel in refractory status epilepticus: a case series.

Perampanel is a selective non-competitive antagonist of AMPA receptors, and the first agent of this class to become available for the treatment of epilepsy. It could be a useful tool for treatment of refractory status epilepticus (RSE). We describe a series of eight RSE cases treated with Perampanel. Perampanel was successful in terminating SE in all the described cases. Only in one patient a severe psychomotor agitation occurred, but without needing PER discontinuation. No other adverse events were observed. Our case series of eight patients, albeit small, broadens the clinical experiences on the efficacy and safety of PER as a treatment for RSE. It may also support the early use of PER, considering the role of AMPA receptors in sustaining epileptic firing in SE. Further studies are warranted to clarify the potential of Perampanel in the treatment of status epilepticus and, in particular, in RSE.

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.

Ketamine modulates the exploratory dynamics and homebase-related behaviors of adult zebrafish

Anxiety is a protective behavior when animals face aversive conditions, but commonly associated with various neuropsychiatric disorders when exacerbated. Drug repurposing has emerged as a valuable strategy to use existing pharmaceuticals for new therapeutic purposes. Ketamine, traditionally used as an anesthetic, acts as a non-competitive antagonist of the N-methyl-d-aspartate (NMDA) receptor, and evidence has shown potential anxiolytic and antidepressant effects at subanesthetic doses. However, the influence of ketamine on multiple behavioral domains in vertebrates is not completely understood. Here, we evaluated the potential modulatory effect of ketamine on the spatio-temporal exploratory dynamics and homebase-related behaviors in adult zebrafish using the open field test (OFT). Animals were exposed to subanesthetic concentrations of ketamine (0, 2, 20, and 40 mg/L) for 20 min and locomotion- exploration- and homebase-related behaviors were assessed in a single 30-min trial. Our data revealed that ketamine (20 and 40 mg/L) induced hyperlocomotion, as verified by the increased total distance traveled. All concentrations tested elicited circling behavior, a stereotyped-like response which gradually reduced across the periods of test. We also observed modulatory effects of ketamine on the spatio-temporal exploratory pattern, in which the reduced thigmotaxis and homebase activity, associated with the increased average length of trips were suggestive of anxiolytic-like effects. Collectively, our novel findings support the modulatory effects of ketamine on the spatio-temporal exploratory activity, as well as the utility of homebase-related measurements to evaluate the behavioral dynamics of zebrafish.

Recreational ketamine use and its impact on health

Ketamine, also known as 2-(2-chlorophenyl)-2-(methylamino)-cyclohexanone, is a dissociative anesthetic that has gained popularity as a recreational substance among young people, especially in nightclubs and at parties. It acts as a noncompetitive NMDA receptor antagonist, inducing a dissociative state that manifests as catalepsy, unconsciousness and amnesia. Recreational use of ketamine and the number of illicit seizures of ketamine have increased in recent years, prompting a review of current evidence on its toxicity. Recreational ketamine use is associated with a number of toxic effects, both acute and chronic. Predominant among the acute effects are psychotic symptoms, hallucinations and aggression, which can lead to serious injuries. Chronic ketamine use leads to intractable urological problems and neuropsychiatric problems, Long-term effects also include gastrointestinal problems such as abdominal pain and liver function abnormalities. This review summarizes current evidences on the acute and chronic ketamine toxicity associated with its recreational use.

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.

Development and Validation of a Simple UV-HPLC Method to Quantify the Memantine Drug Used in Alzheimer's Treatment.

Memantine, a non-competitive NMDA receptor antagonist, is used to treat Alzheimer's disease. Therefore, loading memantine in nanoparticles (NPs) could be an essential tool to improve the treatment effectiveness while reducing drug toxicity. Even though some approaches have been described to quantify memantine, none reported optimized methods using high-performance liquid chromatography resorting to ultraviolet detection (UV-HPLC) to determine encapsulation in NPs. The present research developed a HPLC method using pre-column derivatization for quantitatively analyzing memantine hydrochloride in NPs. Memantine was derivatized using 9-fluorenylmethyl chloroformate (FMOC). The developed method was fully validated regarding suitability, specificity, linearity, sensitivity, precision, accuracy, and robustness according to the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use guidelines. The retention time of memantine was 11.393 ± 0.003 min, with a mean recovery of 92.9 ± 3.7%. The new chromatographic method was validated and found to respond linearly over 5-140 μg/mL, with a high coefficient of determination. Intraday precision lay between 3.6% and 4.6%, and interday precision between 4.2% and 9.3%. The stability of memantine was also tested at 4 °C and -20 °C, and no signs of decay were found for up to 6 months. The new method was properly validated and proved simple, sensitive, specific, accurate, and precise for determining memantine encapsulation efficiency in lipid NPs. Greenness was evaluated, presenting a final score of 0.45. In the future, this methodology could also be applied to quantify memantine in different nanoformulations.

Structural basis of TRPV1 inhibition by SAF312 and cholesterol

Transient Receptor Potential Vanilloid 1 (TRPV1) plays a central role in pain sensation and is thus an attractive pharmacological drug target. SAF312 is a potent, selective, and non-competitive antagonist of TRPV1 and shows promising potential in treating ocular surface pain. However, the precise mechanism by which SAF312 inhibits TRPV1 remains poorly understood. Here, we present the cryo-EM structure of human TRPV1 in complex with SAF312, elucidating the structural foundation of its antagonistic effects on TRPV1. SAF312 binds to the vanilloid binding pocket, preventing conformational changes in S4 and S5 helices, which are essential for channel gating. Unexpectedly, a putative cholesterol was found to contribute to SAF312’s inhibition. Complemented by mutagenesis experiments and molecular dynamics simulations, our research offers substantial mechanistic insights into the regulation of TRPV1 by SAF312, highlighting the interplay between the antagonist and cholesterol in modulating TRPV1 function. This work not only expands our understanding of TRPV1 inhibition by SAF312 but also lays the groundwork for further developments in the design and optimization of TRPV1-related therapies.

Blood Vessels

Abstract: One of the primary target tissues for inflammatory and allergy mediators is the blood vessel, and cytokines have a variety of impacts on it. We describe the usefulness of isolated blood vessels immersed in organ baths as a valuable source of pharmacological data. Contractility assays provide strong potency and selectivity data on agonists, partial agonists, and competitive or noncompetitive antagonists; however, their use in the bioassay of vasoactive drugs is gradually being replaced by more advanced analytical techniques. The human umbilical vein, for instance, has been widely utilized to identify bradykinin B2 receptor ligands. Isolated segments of vascular tissue are highly reactive living tissues, particularly in terms of regulating gene products associated with inflammation (e.g., kinin B1 receptor). The venule’s extremely thin walls have the potential to burst due to their high volume. Venules allow blood to move into larger veins. Both veins and arteries have three layers in their walls. On the other hand, venous pressure is modest. Veins are less elastic and have thin walls, allowing them to maintain a high blood circulation rate. The venous system’s high capacitance enables it to store a significant amount of blood at comparatively low pressures, containing around 75% of the circulating blood at any given time. The veins’ one-way valves permit blood to move forward toward the heart through muscle contractions.

Administration of low dose intranasal ketamine exerts a neuroprotective effect on whole brain irradiation injury model in wistar rats.

Exposure to ionizing radiation leads to oxidative stress and neuroinflammation, resulting in neurocognitive impairments. Adverse effects are also associated with glutamate-induced excitotoxicity due to alterations in the composition of glutamate receptors. Ketamine, which is a noncompetitive NMDA glutamate receptor antagonist, has been stated to exert an impact on glutamatergic receptors. This study aims to reveal the possible alleviating or preventive effects of ketamine, which maintains glutamate homeostasis and decreases neurodegeneration, in a radiation-induced neurotoxicity model. Twenty-one female Wistar Queryrats were included in the study and 14 of these underwent whole brain irradiation (IR) with a 20 Gray single dose. Animals were allocated into three groups. Group 1: Normal control; Group 2: Placebo / IR + Saline; Group 3: IR + Ketamine. Ketamine was administered in addition to IR to rats in Group 3. The one-way ANOVA statistical test was used to compare groups. The value of p < 0.05 was considered statistically significant. When administered in addition to irradiation, ketamine treatment significantly increased scores in the three-chamber sociability test, open field test, and passive avoidance learning test. It also raised neuron counts in the hippocampal CA1 and CA3 regions as well as in Purkinje cells, and enhanced levels of brain-derived neurotrophic factor and tyrosine receptor kinase-B. Furthermore, ketamine administration resulted in decreased levels of glial fibrillary acidic protein, malondialdehyde, and tumor necrosis factor-alpha, indicating a reduction in neuroinflammation and oxidative stress. Ketamine exerted a significant protective impact on radiation-induced neurocognitive impairments and enhanced social-memory capacity by reducing neuronal loss, oxidative stress, and neuroinflammation. Our findings suggest that ketamine is beneficial in the treatment or prevention of neurodegeneration via the regulation of the BDNF/TrkB signaling pathway besides decreasing neuroinflammation and blocking NMDA receptors.

NMDA Receptors and Indices of Energy Metabolism in Erythrocytes: Missing Link to the Assessment of Efficiency of Oxygen Transport in Hepatic Encephalopathy.

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome that develops in patients with severe liver dysfunction and/or portocaval shunting. Despite more than a century of research into the relationship between liver damage and development of encephalopathy, pathogenetic mechanisms of hepatic encephalopathy have not yet been fully elucidated. It is generally recognized, however, that the main trigger of neurologic complications in hepatic encephalopathy is the neurotoxin ammonia/ammonium, concentration of which in the blood increases to toxic levels (hyperammonemia), when detoxification function of the liver is impaired. Freely penetrating into brain cells and affecting NMDA-receptor-mediated signaling, ammonia triggers a pathological cascade leading to the sharp inhibition of aerobic glucose metabolism, oxidative stress, brain hypoperfusion, nerve cell damage, and formation of neurological deficits. Brain hypoperfusion, in turn, could be due to the impaired oxygen transport function of erythrocytes, because of the disturbed energy metabolism that occurs in the membranes and inside erythrocytes and controls affinity of hemoglobin for oxygen, which determines the degree of oxygenation of blood and tissues. In our recent study, this causal relationship was confirmed and novel ammonium-induced pro-oxidant effect mediated by excessive activation of NMDA receptors leading to impaired oxygen transport function of erythrocytes was revealed. For a more complete evaluation of "erythrocytic" factors that diminish brain oxygenation and lead to encephalopathy, in this study, activity of the enzymes and concentration of metabolites of glycolysis and Rapoport-Lubering shunt, as well as morphological characteristics of erythrocytes from the rats with acute hyperammoniemia were determined. To elucidate the role of NMDA receptors in the above processes, MK-801, a non-competitive receptor antagonist, was used. Based on the obtained results it can be concluded that it is necessary to consider ammonium-induced morphofunctional disorders of erythrocytes and hemoglobinemia which can occur as a result of alterations in highly integrated networks of metabolic pathways may act as an additional systemic "erythrocytic" pathogenetic factor to prevent the onset and progression of cerebral hypoperfusion in hepatic encephalopathy accompanied by hyperammonemia.

Identification of aryl hydrocarbon receptor allosteric antagonists from clinically approved drugs.

The human aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, plays a pivotal role in a diverse array of pathways in biological and pathophysiological events. This position AhR as a promising target for both carcinogenesis and antitumor strategies. In this study we utilized computational modeling to screen and identify FDA-approved drugs binding to the allosteric site between α2 of bHLH and PAS-A domains of AhR, with the aim of inhibiting its canonical pathway activity. Our findings indicated that nilotinib effectively fits into the allosteric pocket and forms interactions with crucial residues F82, Y76, and Y137. Binding free energy value of nilotinib is the lowest among top hits and maintains stable within its pocket throughout entire (MD) simulations time. Nilotinib has also substantial interactions with F295 and Q383 when it binds to orthosteric site and activate AhR. Surprisingly, it does not influence AhR nuclear translocation in the presence of AhR agonists; instead, it hinders the formation of the functional AhR-ARNT-DNA heterodimer assembly, preventing the upregulation of regulated enzymes like CYP1A1. Importantly, nilotinib exhibits a dual impact on AhR, modulating AhR activity via the PAS-B domain and working as a noncompetitive allosteric antagonist capable of blocking the canonical AhR signaling pathway in the presence of potent AhR agonists. These findings open a new avenue for the repositioning of nilotinib beyond its current application in diverse diseases mediated via AhR.

Antidepressant effects of selective adenosine receptor antagonists targeting the A1 and A2A receptors administered jointly with NMDA receptor ligands: behavioral, biochemical and molecular investigations in mice

BackgroundThe objective of the study was to ascertain the antidepressant potential of the co-administration of NMDA receptor ligands and selective adenosine A1 and A2A receptor antagonists.MethodsThe forced swim test (FST) and spontaneous locomotor activity test were carried out in adult male naïve mice. Before the behavioral testing, animals received DPCPX (a selective adenosine A1 receptor antagonist, 1 mg/kg) or istradefylline (a selective adenosine A2A receptor antagonist, 0.5 mg/kg) in combination with L–701,324 (a potent NMDA receptor antagonist, 1 mg/kg), D–cycloserine (a partial agonist at the glycine recognition site of NMDA receptor, 2.5 mg/kg), CGP 37849 (a competitive NMDA receptor antagonist, 0.3 mg/kg) or MK–801 (a non-competitive NMDA receptor antagonist, 0.05 mg/kg). Additionally, serum BDNF level and the mRNA level of the Adora1, Comt, and Slc6a15 genes in the murine prefrontal cortex were determined.ResultsThe obtained results showed that DPCPX and istradefylline administered jointly with NMDA receptor ligands (except for DPCPX + D–cycloserine combination) produced an antidepressant effect in the FST in mice without enhancement in spontaneous motility of animals. An elevation in BDNF concentration was noted in the D–cycloserine-treated group. Adora1 expression increased with L–701,324, DPCPX + D–cycloserine, and DPCPX + CGP 37849, while D–cycloserine, CGP 37849, and MK–801 led to a decrease. Comt mRNA levels dropped with DPCPX + L–701,324, istradefylline + L–701,324/CGP 37849 but increased with D–cycloserine, MK–801, CGP 37849 and DPCPX + MK–801/ CGP 37849. Slc6a15 levels were reduced by D–cycloserine, DPCPX + L–701,324 but rose with DPCPX + CGP 37849/MK–801 and istradefylline + D–cycloserine/MK–801/CGP 37849.ConclusionOur study suggests that selective antagonists of adenosine receptors may enhance the antidepressant efficacy of NMDA receptor ligands highlighting a potential synergistic interaction between the adenosinergic and glutamatergic systems. Wherein, A2A receptor antagonists are seen as more promising candidates in this context. Given the intricate nature of changes in BDNF levels and the expression of Adora1, Comt, and Slc6a15 seen after drug combinations exerting antidepressant properties, further research and integrative approaches are crucial understand better the mechanisms underlying their antidepressant action.

Activation of μ receptors by SR-17018 through a distinctive mechanism

Agonists at μ opioid receptors relieve acute pain, however, their long-term use is limited by side effects, which may involve β-arrestin2. Agonists biased against β-arrestin2 recruitment may be advantageous. However, the classification of bias may be compromised by assays utilising overexpressed μ receptors which overestimate efficacy for G-protein activation. There is a need for re-evaluation with restricted receptor availability to determine accurate agonist efficacies. We depleted μ receptor availability in PathHunter CHO cells using the irreversible antagonist, β-funaltrexamine (β-FNA), and compared efficacies and apparent potencies of twelve agonists, including several previously reported as biased, in β-arrestin2 recruitment and cAMP assays. With full receptor availability all agonists had partial efficacy for stimulating β-arrestin2 recruitment relative to DAMGO, while only TRV130 and buprenorphine were partial agonists as inhibitors of cAMP accumulation. Limiting receptor availability by prior exposure to β-FNA (100 nM) revealed morphine, oxycodone, PZM21, herkinorin, U47700, tianeptine and U47931e are also partial agonists in the cAMP assay. The efficacies of all agonists, except SR-17018, correlated between β-arrestin2 recruitment and cAMP assays, with depleted receptor availability in the latter. Furthermore, naloxone and cyprodime exhibited non-competitive antagonism of SR-17018 in the β-arrestin2 recruitment assay. Limited antagonism by naloxone was also non-competitive in the cAMP assay, while cyprodime was competitive. Furthermore, SR-17018 only negligibly diminished β-arrestin2 recruitment stimulated by DAMGO (1 μM), whereas fentanyl, morphine and TRV130 all exhibited the anticipated competitive inhibition. The data suggest that SR-17018 achieves bias against β-arrestin2 recruitment through interactions with μ receptors outside the orthosteric agonist site.This article is part of the Special Issue on “Ligand Bias”.

Memantine alleviates cognitive impairment and hippocampal morphology injury in a mouse model of chronic alcohol exposure

Alcohol-related cognitive impairment (ARCI) is highly prevalent among patients with alcohol abuse and dependence. The pathophysiology of ARCI, pivotal for refined therapeutic approaches, is not fully elucidated, posing a risk of progression to severe neurological sequelae such as Korsakoff's syndrome (KS) and Alcohol-Related Dementia (ARD). This study ventures into the underlying mechanisms of chronic alcohol-induced neurotoxicity, notably glutamate excitotoxicity and cytoskeletal disruption, and explores the therapeutic potential of Memantine, a non-competitive antagonist of the N-methyl-d-aspartate (NMDA) receptor known for its neuroprotective effect against excitotoxicity. Our investigation centers on the efficacy of Memantine in mitigating chronic alcohol-induced cognitive and hippocampal damages in vivo. Male C57BL/6J mice were subjected to 30 % (v/v, 6.0 g/kg) ethanol via intragastric administration alongside Memantine co-treatment (10 mg/kg/day, intraperitoneally) for six weeks. The assessment involved Y maze, Morris water maze, and novel object recognition tests to evaluate spatial and recognition memory deficits. Histopathological evaluations of the hippocampus were conducted to examine the extent of alcohol-induced morphological changes and the potential protective effect of Memantine. The findings reveal that Memantine significantly improves chronic alcohol-compromised cognitive functions and mitigates hippocampal pathological changes, implicating a moderating effect on the disassembly of actin cytoskeleton and microtubules in the hippocampus, induced by chronic alcohol exposure. Our results underscore Memantine's capability to attenuate chronic alcohol-induced cognitive and hippocampal morphological harm may partly through regulating cytoskeleton dynamics, offering valuable insights into innovative therapeutic strategies for ARCI.

Cardioprotective and antispasmodic effects of Humulus lupulus (Hops) in an oral subacute treatment in rats

Hops (Humulus lupulus) was used to treat menopausal symptoms because it contains phytoestrogens. Since these compounds prevent cardiac ischemic diseases, it was evaluated whether oral administration of an ethanol extract (Hops-T) to rats during a week could reduce cardiac post-ischemic dysfunction. Moreover, its effects on visceral peristaltism and the mechanisms of action were studied. Rat isolated hearts were perfused inside a calorimeter, left intraventricular pressure and calorimetrical signals were recorded during ischemia/reperfusion. The NO-synthases and mKATP channels roles were evaluated by respectively blocking them with L-NAME and 5-HD before ischemia. After the experiment, western-blots for cellular pathways (p-AKT, p-PKCϵ, GSK3b and BCL-2) were done. In isolated intestinal, bladder and uterine rat tissues, contractile carbachol concentration-response curves (CCh-CRCs) were performed. The HPLC-DAD mainly showed prenylated flavonoids, beta acids and isoflavones. Hops-T increased contractile and energetic recoveries more significantly in the male rat hearts compared to females, due to beneficial NO production and mitochondrial mKATP channels activation. However, the p-AKT, p-PKCϵ, GSK3b or BCL-2 expressions were not affected after reperfusion. Hops-T inhibited CCh-CRCs in intestinal, bladder and uterine tissues through a non-competitive mechanism. Additionally, it showed a non-competitive antagonism of the Ca2+-CRCs in bladder tissues, similar to the effects observed with verapamil. In conclusion, oral Hops-T prevented cardiac mitochondrial and contractile ischemic dysfunction, and it was a good visceral antispasmodic medicine by interfering with Ca2+ influx. This is a significant finding since it pre-clinically supports the use of hops extract for prevention of visceral spasms and cardiac diseases associated with coronary insufficiency.

The Involvement of the Serotonergic System in Ketamine and Fluoxetine Combination-induced Cognitive Impairments in Mice.

Glutamatergic N-methyl-D-aspartate (NMDA) receptors play vital roles in memory formation. Changes in the activity of these receptors influence memory processes. Ketamine is a noncompetitive NMDA receptor antagonist drug with promising mood-altering and pain-reducing effects in low doses. These effects are believed to be related to altered serotonergic transmission. The present study investigated the involvement of the serotonergic system in low-dose ketamine administrations' effects on memory acquisition, consolidation, and retrieval processes. Sixty-four male BALB/c mice were used in this experiment and separated into 8t groups. Mice were treated subchronically with a selective serotonin reuptake inhibitor, fluoxetine, and a serotonin depletion agent, p-chlorophenylalanine (pCPA). A serotonin antagonist, methiothepin, and ketamine were acutely administered 60 minutes before or after the behavioral tests. A passive avoidance (PA) test measured emotional memory acquisition, consolidation, and retrieval processes. Hippocampi malondialdehyde (MDA) levels were analyzed, and histopathological examinations were performed. Ketamine alone did not significantly affect memory encoding processes in the PA test, while the ketamine-fluoxetine combination disrupted memory consolidation. Fluoxetine negatively affected the memory acquisition process, which was normalized during the consolidation and retrieval trials. Drug applications did not significantly alter hippocampal MDA levels. In all ketamine-applied groups, histopathologic alterations were evident. Low-dose ketamine administration induces neurodegeneration, and it also impairs memory functions when combined with fluoxetine, indicating increased serotonergic transmission may be involved in the memory-impairing and neurotoxic effects of ketamine.

Evaluation of the potential role of glutamatergic, cholinergic, and nitrergic systems in the dopamine release induced by the pesticide glyphosate in rat striatum.

Glyphosate (GLY) is a pesticide that severely alters nigrostriatal dopaminergic neurotransmission, inducing great increases in dopamine release from rat dorsal striatum. This GLY-induced striatal dopamine overflow occurs through mechanisms not yet fully understood, hence the interest in evaluating the role of other neurotransmitter systems in such effects. So, the main objective of this mechanistic study was to evaluate the possible mediation of the glutamatergic, cholinergic, and nitrergic systems in the GLY-induced in vivo dopamine release from rat dorsal striatum. The extracellular dopamine levels were measured by cerebral microdialysis and HPLC with electrochemical detection. Intrastriatal administration of GLY (5mmol/L) significantly increased the dopamine release (1102%). Pretreatment with MK-801 (50 or 400 μmol/L), a non-competitive antagonist of NMDA receptors, significantly decreased the effect of GLY (by 70% and 74%, respectively), whereas AP-5 (400 μmol/L), a competitive antagonist of NMDA receptors, or CNQX (500 μmol/L), an AMPA/kainate receptor antagonist, had no significant effect. Administration of the nitric oxide synthase inhibitors, L-nitroarginine (L-NAME, 100 μmol/L) or 7-nitroindazole (7-NI, 100 μmol/L), also did not alter the effect of GLY on dopamine release. Finally, pretreatment of the animals with mecamylamine, an antagonist of nicotinic receptors, decreased the effect of GLY on dopamine release by 49%, whereas atropine, a muscarinic antagonist, had no significant effect. These results indicate that GLY-induced dopamine release largely depends on the activation of NMDA and nicotinic receptors in rat dorsal striatum. Future research is needed to determine the effects of this pesticide at environmentally relevant concentrations.

Adenosine A2A and dopamine D2 receptor interaction controls fatigue resistance.

Introduction: Caffeine and the selective A2A receptor antagonist SCH58261 both have ergogenic properties, effectively reducing fatigue and enhancing exercise capacity. This study investigates in male Swiss mice the interaction between adenosine A2A receptors and dopamine D2 receptors controlling central fatigue, with a focus on the striatum where these receptors are most abundant. Methods: We employed DPCPX and SCH58261 to antagonize A1 and A2A receptors, caffeine as a non-competitive antagonist for both receptors, and haloperidol as a D2 receptor antagonist; all compounds were tested upon systemic application and caffeine and SCH58261 were also directly applied in the striatum. Behavioral assessments using the open field, grip strength, and treadmill tests allowed estimating the effect of treatments on fatigue. Results and discussion: The results suggested a complex interplay between the dopamine and adenosine systems. While systemic DPCPX had little effect on motor performance or fatigue, the application of either caffeine or SCH58261 was ergogenic, and these effects were attenuated by haloperidol. The intra-striatal administration of caffeine or SCH58261 was also ergogenic, but these effects were unaffected by haloperidol. These findings confirm a role of striatal A2A receptors in the control of central fatigue but suggest that the D2 receptor-mediated control of the ergogenic effects of caffeine and of A2A receptor antagonists might occur outside the striatum. This prompts the need of additional efforts to unveil the role of different brain regions in the control of fatigue.

Ketamine administration causes cognitive impairment by destroying the circulation function of the glymphatic system

BackgroundKetamine, as a non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptors, was originally used in general anesthesia. Epidemiological data show that ketamine has become one of the most commonly abused drugs in China. Ketamine administration might cause cognitive impairment; however, its molecular mechanism remains unclear. The glymphatic system is a lymphoid system that plays a key role in metabolic waste removal and cognitive regulation in the central nervous system. MethodsFocusing on the glymphatic system, this study evaluated the behavioral performance and circulatory function of the glymphatic system by building a short-term ketamine administration model in mice, and detected the expression levels of the 5-HT2c receptor, ΔFosb, Pten, Akt, and Aqp4 in the hippocampus. Primary astrocytes were cultured to verify the regulatory relationships among related indexes using a 5-HT2c receptor antagonist, a 5-HT2c receptor short interfering RNA (siRNA), and a ΔFosb siRNA. ResultsKetamine administration induced ΔFosb accumulation by increasing 5-HT2c receptor expression in mouse hippocampal astrocytes and primary astrocytes. ΔFosb acted as a transcription factor to recognize the AATGATTAAT bases in the 5′ regulatory region of the Aqp4 gene (−1096 bp to −1087 bp), which inhibited Aqp4 expression, thus causing the circulatory dysfunction of the glymphatic system, leading to cognitive impairment. ConclusionsAlthough this regulatory mechanism does not involve the Pten/Akt pathway, this study revealed a new mechanism of ketamine-induced cognitive impairment in non-neuronal systems, and provided a theoretical basis for the safety of clinical treatment and the effectiveness of withdrawal.