BACKGROUND: The pathophysiology and molecular mechanisms of schizophrenia (SCZ) remain unclear, and the effective treatment resources are still limited. The goal of this study is to identify the expression of AQP4 in SCZ patients and explore whether AQP4 inhibition could ameliorate schizophrenia-like behaviors and its mechanisms.
METHODS: Microarray datasets of PFC compared with healthy control were searched in the Gene Expression Omnibus (GEO) database, and differentially expressed genes (DEGs) were analyzed with the GEO2R online tool. The Venny online tool and metascape online software were used to identify common abnormally expressed genes and conduct cell type signature enrichment analysis. SCZ mouse models were induced with MK-801, an NMDA receptor antagonist (intraperitoneal injection, 0.1 mg/kg/day for 7 days), and C6 cell models were treated with 100 μM MK-801. RT-qPCR, Western Blotting, and immunofluorescence were employed to determine the expression of AQP4, proinflammatory cytokines, and GFAP. Open field tests and social interaction tests were performed to evaluate the schizophrenia-like behaviors.
RESULTS: Bioinformatics analysis identified upregulation of AQP4 in the PFC of SCZ patients compared with healthy controls. Cell type signature enrichment analysis showed that all three DEGs lists were strongly enriched in the FAN EMBRYONIC CTX ASTROCYTE 2 category. Upregulation of AQP4 was also observed in MK-801-treated C6 cells and the PFC of MK-801-induced SCZ mouse model. Moreover, AQP4 inhibition with TGN-020 (an inhibitor of AQP4) improved anxiety-like behavior and social novelty preference defects in MK-801-treated mice. AQP4 inhibition also reduced the expression of IL-1β, IL-6, and TNF-α in MK-801-treated C6 cells and mouse model.
CONCLUSIONS: AQP4 is upregulated in the PFC of SCZ patients compared with healthy controls. AQP4 inhibition could alleviate the anxiety-like behavior and social novelty defects in MK-801-treated mice, this may be due to the role of AQP4 in the regulation of the expression of proinflammatory cytokines.

BACKGROUND: Each year, 3-4% of the global population experiences post-traumatic stress disorder (PTSD), a chronic mental disorder with significant social and economic repercussions. Although it has been shown that ketamine can effectively alleviate PTSD symptoms in individuals, the specific mechanism of action underlying its anti-PTSD effects remains unclear. In this study, we investigated how a single, low dose of ketamine affected the glycogen synthase kinase 3β (GSK-3β)/glucocorticoid receptor (GR) signaling pathway in a single prolonged stress (SPS)-induced PTSD rat model.
METHODS: After establishing the model, stress-related behavioral alterations in the rats were assessed following intraperitoneal injections of ketamine (10 mg/kg) and GSK-3β antagonist SB216763 (5 mg/kg). In the hippocampus, alterations in the expression of specific proteins implicated in PTSD development, such as GR, brain-derived neurotrophic factor (BDNF), GSK-3β, and phosphorylated glycogen synthase kinase 3β (p-GSK-3β), were assessed. We also measured changes in the mRNA expression levels of GR, BDNF, GSK-3β, FK501 binding protein 51 (FKBP5), and corticotropin-releasing hormone (CRH), as well as synaptic ultrastructure, in the hippocampus, and measured changes in corticosterone levels in the blood.
RESULTS: SPS induced anxiety-like and depression-like behaviors in rats and induced morphological changes in synapse, which were accompanied by higher GSK-3β protein expression and conversely, decreased expression of GR, BDNF, p-GSK-3β, FKBP5 and CRH. Intraperitoneal administration of ketamine (10 mg/kg) after SPS prevented SPS-induced anxiety-like behaviors. Most importantly, ketamine attenuated SPS-induced dysfunctions in GSK-3β/GR signaling and synaptic deficits. Furthermore, treatment with a GSK-3β inhibitor played the same effect as ketamine on behavioral changes of SPS model rats.
CONCLUSIONS: Single doses of ketamine effectively ameliorate SPS-induced anxiety-like symptoms, potentially by improving synaptic plastic in the hippocampus by regulating GSK-3β/GR signaling.

Schizophrenia is a complex neuropsychiatric disorder with positive, negative, and cognitive symptoms. In rats, sub-chronic administration of ketamine is used for the induction of schizophrenia model. Increased locomotor activity is one of the most important features of psychotic-like symptoms in rodents. On the other hand, risperidone is a potent antipsychotic medication that is approved for the treatment of schizophrenia and bipolar disorder. In the present research, we aimed to investigate the effect of sub-chronic treatment of ketamine on cognitive and behavioral functions, and brain-derived neurotrophic factor (BDNF) expression level in the prefrontal cortex. Also, we assessed the efficacy of risperidone on cognitive and behavioral impairments induced by ketamine. Possible sex differences were also measured. Ketamine was intraperitoneally injected at the dose of 30 mg/kg for five consecutive days. Risperidone was also intraperitoneally injected at the dose of 2 mg/kg. Novel object recognition memory, pain threshold, locomotor activity, rearing behavior, and BDNF level were evaluated. The results showed that ketamine injection for five consecutive days impaired the acquisition of long-term recognition memory and decreased BDNF level in the prefrontal cortex in both sexes. Also, it decreased pain threshold in females, increased rearing behavior in males, and induced hyperlocomotion with greater effect in females. On the other hand, risperidone restored or attenuated the effect of ketamine on all the behavioral effects and BDNF level. In conclusion, we suggested that there were sex differences in the effects of ketamine on pain perception, locomotion, and rearing behavior in a rat model of schizophrenia.

Monocular deprivation (MD) causes an initial decrease in synaptic responses to the deprived eye in juvenile mouse primary visual cortex (V1) through Hebbian long-term depression (LTD). This is followed by a homeostatic increase, which has been attributed either to synaptic scaling or to a slide threshold for Hebbian long-term potentiation (LTP) rather than scaling. We therefore asked in mice of all sexes whether the homeostatic increase during MD requires GluN2B-containing NMDA receptor activity, which is required to slide the plasticity threshold but not for synaptic scaling. Selective GluN2B blockade from 2-6 d after monocular lid suture prevented the homeostatic increase in miniature excitatory postsynaptic current (mEPSC) amplitude in monocular V1 of acute slices and prevented the increase in visually evoked responses in binocular V1 in vivo. The decrease in mEPSC amplitude and visually evoked responses during the first 2 d of MD also required GluN2B activity. Together, these results support the idea that GluN2B-containing NMDA receptors first play a role in LTD immediately following eye closure and then promote homeostasis during prolonged MD by sliding the plasticity threshold in favor of LTP.

Glutamate activates the NMDARs, significantly affecting multiple processes such as learning, memory, synaptic integration, and excitatory transmission in the central nervous system. Uncontrolled activation of NMDARs is a significant contributor to synaptic dysfunction. Having a properly functioning NMDAR and synapse is crucial for maintaining neuronal communication. In addition, the dysfunction of NMDAR and synapse function could contribute to the development of neurological disorders at the neuronal level; hence, targeting NMDARs with antagonists in the fight against neurological disorders is a promising route. Recently published results from the animal study on different kinds of brain diseases like stroke, epilepsy, tinnitus, ataxia, Alzheimer\'s disease, Parkinson\'s disease, and spinal cord injury have demonstrated promising therapeutic scopes. Several NMDA receptor antagonists, such as memantine, MK801, ketamine, ifenprodil, gacyclidine, amantadine, agmatine, etc., showed encouraging results against different brain disease mouse models. Given the unique expression of different subunits of the well-organized NMDA receptor system by neurons. It could potentially lead to the development of medications specifically targeting certain receptor subtypes. For a future researcher, conducting more targeted research and trials is crucial to fully understand and develop highly specific medications with good clinical effects and potential neuroprotective properties.

Contextual fear conditioning is a protocol used to assess associative learning across species, including fish. Here, our goal was to expand the analysis of behavioral parameters that may reflect aversive behaviors in a contextual fear conditioning protocol using adult zebrafish (Danio rerio) and to verify how such parameters can be modulated. First, we analyzed the influence of an aversive stimulus (3 mild electric shocks for 5 s each at frequencies of 10, 100 or 1000 Hz) on fish behavior, and their ability to elicit fear responses in the absence of shock during a test session. To confirm whether the aversive responses are context-dependent, behaviors were also measured in a different experimental environment in a test session. Furthermore, we investigated the effects of dizocilpine (MK-801, 2 mg/kg, i.p.) on fear-related responses. Zebrafish showed significant changes in baseline activity immediately after shock exposure in the training session, in which 100 Hz induced robust contextual fear responses during the test session. Importantly, when introduced to a different environment, animals exposed to the aversive stimulus did not show any differences in locomotion and immobility-related parameters. MK-801 administered after the training session reduced fear responses during the test, indicating that glutamate NMDA-receptors play a key role in the consolidation of contextual fear-related memory in zebrafish. In conclusion, by further exploring fear-related behaviors in a contextual fear conditioning task, we show the effects of different shock frequencies and confirm the importance of context on aversive responses for associative learning in zebrafish. Additionally, our data support the use of zebrafish in contextual fear conditioning tasks, as well as for advancing pharmacological studies related to associative learning in translational neurobehavioral research.

N-methyl-D-aspartate receptors (NMDARs) play a significant role in developing several central nervous system (CNS) disorders. Currently, memantine, used for treating Alzheimer\'s disease, and ketamine, known for its anesthetic and antidepressant properties, are two clinically used NMDAR open-channel blockers. However, despite extensive research into NMDAR modulators, many have shown either harmful side effects or inadequate effectiveness. For instance, dizocilpine (MK-801) is recognized for its powerful psychomimetic effects due to its high-affinity and nearly irreversible inhibition of the GluN1/GluN2 NMDAR subtypes. Unlike ketamine, memantine and MK-801 also act through a unique, low-affinity \"membrane-to-channel inhibition\" (MCI). We aimed to develop an open-channel blocker based on MK-801 with distinct inhibitory characteristics from memantine and MK-801. Our novel compound, K2060, demonstrated effective voltage-dependent inhibition in the micromolar range at key NMDAR subtypes, GluN1/GluN2A and GluN1/GluN2B, even in the presence of Mg2+. K2060 showed reversible inhibitory dynamics and a partially trapping open-channel blocking mechanism with a significantly stronger MCI than memantine. Using hippocampal slices, 30 µM K2060 inhibited excitatory postsynaptic currents in CA1 hippocampal neurons by ∼51 %, outperforming 30 µM memantine (∼21 % inhibition). K2060 exhibited No Observed Adverse Effect Level (NOAEL) of 15 mg/kg upon intraperitoneal administration in mice. Administering K2060 at a 10 mg/kg dosage resulted in brain concentrations of approximately 2 µM, with peak concentrations (Tmax) achieved within 15 minutes. Finally, applying K2060 with trimedoxime and atropine in mice exposed to tabun improved treatment outcomes. These results underscore K2060\'s potential as a therapeutic agent for CNS disorders linked to NMDAR dysfunction.

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.

Ketamine is an NMDA (N-methyl-d-aspartate) glutamate receptor antagonist, which has a myriad of dose-dependent pharmacological and behavioral effects, including anesthetic, sedative, amnestic, analgesic, and anti-inflammatory properties. Intriguingly, ketamine at subanesthetic doses displays a relevant profile both in mimicking symptoms of schizophrenia and also as the first fast-acting treatment for depression. Here, we present an overview of the state-of-the-art knowledge about ketamine as an antidepressant as well as a pharmacological model of schizophrenia in animal models and human participants. Ketamine\'s dual effect appears to arise from its mechanism of action involving NMDA receptors, with both immediate and downstream consequences being triggered as a result. Finally, we discuss the feasibility of a unified approach linking the glutamatergic hypothesis of schizophrenia to the promising preclinical and clinical success of ketamine in the treatment of refractory depression.

Promising new pharmacological strategies for the enhancement of cognition target either nicotinic acetylcholine receptors (nAChR) or N-methyl-D-aspartate receptors (NMDAR). There is also an increasing interest in low-dose combination therapies co-targeting the above neurotransmitter systems to reach greater efficacy over the monotreatments and to reduce possible side effects of high-dose monotreatments. In the present study, we assessed modulatory effects of the α7 nAChR-selective agonist PHA-543613 (PHA), a novel α7 nAChR positive allosteric modulator compound (CompoundX) and the NMDAR antagonist memantine on the in vivo firing activity of CA1 pyramidal neurons in the rat hippocampus. Three different test conditions were applied: spontaneous firing activity, NMDA-evoked firing activity and ACh-evoked firing activity. Results showed that high but not low doses of memantine decreased NMDA-evoked firing activity, and low doses increased the spontaneous and ACh-evoked firing activity. Systemically applied PHA robustly potentiated ACh-evoked firing activity with having no effect on NMDA-evoked activity. In addition, CompoundX increased both NMDA- and ACh-evoked firing activity, having no effects on spontaneous firing of the neurons. A combination of low doses of memantine and PHA increased firing activity in all test conditions and similar effects were observed with memantine and CompoundX but without spontaneous firing activity increasing effects. Our present results demonstrate that α7 nAChR agents beneficially interact with Alzheimer\'s disease medication memantine. Moreover, positive allosteric modulators potentiate memantine effects on the right time and the right place without affecting spontaneous firing activity. All these data confirm previous behavioral evidence for the viability of combination therapies for cognitive enhancement.