NRX-101, a Rapid-Acting Anti-Depressant, Does Not Cause Neurotoxicity Following Ketamine Administration in Preclinical Models.

Agents that act at the N-methyl-D-aspartate receptor (NMDAR), such as ketamine, have gained increasing attention as rapid-acting antidepressants; however, their use has been limited by potential neurotoxicity. Recent FDA guidance requires a demonstration of safety on histologic parameters prior to the initiation of human studies. D-cycloserine (DCS) is a partial NMDA agonist that, along with lurasidone, is being investigated as a treatment for depression. The current study was designed to investigate the neurologic safety profile of DCS. To this end, female Sprague Dawley rats (n = 106) were randomly divided into 8 study groups. Ketamine was administered via tail vein infusion. DCS and lurasidone were administered via oral gavage in escalating doses to a maximum of 2000 mg/kg DCS. To ascertain toxicity, dose escalation with 3 different doses of D-cycloserine/lurasidone was given in combination with ketamine. MK-801, a known neurotoxic NMDA antagonist, was administered as a positive control. Brain tissue was sectioned and stained with H&E, silver, and Fluoro-Jade B stains. No fatalities were observed in any group. No microscopic abnormalities were found in the brain of animal subjects given ketamine, ketamine followed by DCS/lurasidone, or DCS/lurasidone alone. Neuronal necrosis, as expected, was seen in the MK-801 (positive control) group. We conclude that NRX-101, a fixed-dose combination of DCS/lurasidone, when administered with or without prior infusion of IV ketamine was tolerated and did not induce neurotoxicity, even at supratherapeutic doses of DCS.

DHF-7 Ameliorates Behavioral Disorders and White Matter Lesions by Regulating BDNF and Fyn in a Mouse Model of Schizophrenia Induced by Cuprizone and MK-801.

BACKGROUND: Schizophrenia is a psychiatric disorder including multiple clinical symptoms such as severe psychosis and cognitive dysfunction. DHF-7 is a novel dihydroflavanone derivative that was designed and synthesized to treat schizophrenia. This study aimed to investigate the effects and mechanisms of DHF-7 in a mouse model of schizophrenia induced by a combination of cuprizone and MK-801. METHODS: After intragastric administration of DHF-7 for 7 weeks, open field, Y-maze, and novel object recognition tests were performed to detect behavioral changes in the mouse model. White matter lesions and myelin loss were determined using transmission electron microscopy and oil red O staining. Western blotting and immunohistochemistry were used to detect the expression of the related proteins. RESULTS: The results showed that DHF-7 treatment significantly improved cognitive impairment and positive symptoms in the model mice. Moreover, DHF-7 alleviated white matter lesions and demyelination and promoted the differentiation and maturation of oligodendrocytes for remyelination in the corpus callosum of model mice. The mechanistic study showed that DHF-7 increased the expression of brain-derived neurotrophic factor and phosphorylated Fyn, thus activating the tyrosine kinase receptor B (Trk B)/Fyn/N-methyl-D-aspartate receptor subunit 2 B (NMDAR2B) and Raf/mitogen-activated protein kinase (MEK)/ extracellular signal-related kinase (ERK) signaling pathways. CONCLUSIONS: Our results provide an experimental basis for the development of DHF-7 as a novel therapeutic agent for schizophrenia.

Distribution of Aquaporin-4 channels in hippocampus and prefrontal cortex in mk-801-treated balb/c mice.

Functional disorders of the glymphatic system and Aquaporin-4 (AQP-4) channels take part in the pathophysiology of neurodegenerative disease. The aim of this study was to describe the distribution of AQP-4 channels in the prefrontal cortex and hippocampus in a mouse model of NMDA receptor blocking agent-induced schizophrenia-like behavior model. NMDA receptor antagonist MK-801 was used to produce the experimental schizophrenia model. MK-801 injections were administered for eleven days to Balb/c mice intraperitoneally. Beginning from the sixth day of injection, the spatial learning and memory of the mice were tested by the Morris water maze (MWM) task. A group of mice was injected with MK-801 for ten days without the MWM task. Hippocampus and prefrontal specimens were collected from this group. Tissue samples were stained immunohistochemically and AQP-4 channels were examined by electron microscope. Time to find the platform was significantly longer at MK-801 injected group than the control group at the MWM task. Also, time spent at the target quadrant by the MK-801 group was shorter compared to the control group. AQP-4 expression increased significantly at MK-801 group glial cells, neuronal perikaryon, perineuronal and pericapillary spaces. In the MK-801 group, there was remarkable damage in neurons and glial cells. Increased AQP-4 channel expression and neurodegeneration at the MK-801 group induced with schizophrenia-like behavior model. MK-801 induced NMDA receptor blockade causes a decline in cognitive and memory functions. Increased AQP-4 expression at the prefrontal cortex and hippocampus to elicit and transport products of synaptic neurotransmitters and end metabolites is suggested.

4-Methoxycinnamic acid attenuates schizophrenia-like behaviors induced by MK-801 in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Scrophularia buergeriana has been used for traditional medicine as an agent for reducing heat in the blood and for nourishing kidney 'Yin'. Therefore, S. buergeriana might be a potential treatment for mental illness, especially schizophrenia, which may be attenuated by supplying kidney Yin and reducing blood heat. In a pilot study, we found that S. buergeriana alleviated sensorimotor gating dysfunction induced by MK-801. AIM OF THE STUDY: In the present study, we attempted to reveal the active component(s) of S. buergeriana as a candidate for treating sensorimotor gating dysfunction, and we identified 4-methoxycinnamic acid. We explored whether 4-methoxycinnamic acid could affect schizophrenia-like behaviors induced by hypofunction of the glutamatergic neurotransmitter system. MATERIALS AND METHODS: Mice were treated with 4-methoxycinnamic acid (3, 10, or 30 mg/kg, i.g.) under MK-801-induced schizophrenia-like conditions. The effect of 4-methoxycinnamic acid on schizophrenia-like behaviors were explored using several behavioral tasks. We also used Western blotting to investigate which signaling pathway(s) is involved in the pharmacological activities of 4-methoxycinnamic acid. RESULTS: 4-Methoxycinnamic acid ameliorated MK-801-induced prepulse inhibition deficits, social interaction disorders and cognitive impairment by regulating the phosphorylation levels of PI3K, Akt and GSK-3ß signaling in the prefrontal cortex. And there were no adverse effects in terms of catalepsy and motor coordination impairments. CONCLUSION: Collectively, 4-methoxycinnamic acid would be a potential candidate for treating schizophrenia with fewer adverse effects, especially the negative symptoms and cognitive dysfunctions.

Cannabidiol Attenuates MK-801-Induced Cognitive Symptoms of Schizophrenia in the Passive Avoidance Test in Mice.

Schizophrenia is a chronic mental disorder that disturbs feelings and behavior. The symptoms of schizophrenia fall into three categories: positive, negative, and cognitive. Cognitive symptoms are characterized by memory loss or attentional deficits, and are especially difficult to treat. Thus, there is intense research into the development of new treatments for schizophrenia-related responses. One of the possible strategies is connected with cannabidiol (CBD), a cannabinoid compound. This research focuses on the role of CBD in different stages of memory (acquisition, consolidation, retrieval) connected with fear conditioning in the passive avoidance (PA) learning task in mice, as well as in the memory impairment typical of cognitive symptoms of schizophrenia. Memory impairment was provoked by an acute injection of the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (animal model of schizophrenia). Our results revealed that an acute injection of CBD (30 mg/kg; intraperitoneally (i.p.) improved all phases of long-term fear memory in the PA test in mice. Moreover, the acute injection of non-effective doses of CBD (1 or 5 mg/kg; i.p.) attenuated the memory impairment provoked by MK-801 (0.6 mg/kg; i.p.) in the consolidation and retrieval stages of fear memory, but not in the acquisition of memory. The present findings confirm that CBD has a positive influence on memory and learning processes in mice, and reveals that this cannabinoid compound is able to attenuate memory impairment connected with hypofunction of glutamate transmission in a murine model of schizophrenia.

Serotonergic-Muscarinic Interaction within the Prefrontal Cortex as a Novel Target to Reverse Schizophrenia-Related Cognitive Symptoms.

Recent studies revealed that the activation of serotonergic 5-HT1A and muscarinic M1, M4, or M5 receptors prevent MK-801-induced cognitive impairments in animal models. In the present study, the effectiveness of the simultaneous activation of 5-HT1A and muscarinic receptors at preventing MK-801-induced cognitive deficits in novel object recognition (NOR) or Y-maze tests was investigated. Activators of 5-HT1A (F15599), M1 (VU0357017), M4 (VU0152100), or M5 (VU0238429) receptors administered at top doses for seven days reversed MK-801-induced deficits in the NOR test, similar to the simultaneous administration of subeffective doses of F15599 (0.05 mg/kg) with VU0357017 (0.15 mg/kg), VU0152100 (0.05 mg/kg), or VU0238429 (1 mg/kg). The compounds did not prevent the MK-801-induced impairment when administered acutely. Their activity was less evident in the Y-maze. Pharmacokinetic studies revealed high brain penetration of F15599 (brain/plasma ratio 620%), which was detected in the frontal cortex (FC) up to 2 h after administration. Decreases in the brain penetration properties of the compounds were observed after acute administration of the combinations, which might have influenced behavioral responses. This negative effect on brain penetration was not observed when the compounds were administered repeatedly. Based on our results, prolonged administration of a 5-HT1A activator with muscarinic receptor ligands may be effective at reversing cognitive decline related to schizophrenia, and the FC may play a critical role in this interaction.

Synergistic efficacy and diminished adverse effect profile of composite treatment of several ADHD medications.

Although attention-deficit/hyperactivity disorder (ADHD) is widely studied, problems regarding the adverse effect risks and non-responder problems still need to be addressed. Combination pharmacotherapy using standard dose regimens of existing medication is currently being practiced mainly to augment the therapeutic efficacy of each drug. The idea of combining different pharmacotherapies with different molecular targets to alleviate the symptoms of ADHD and its comorbidities requires scientific evidence, necessitating the investigation of their therapeutic efficacy and the mechanisms underlying the professed synergistic effects. Here, we injected male ICR mice with MK-801 to induce ADHD behavioral condition. We then modeled a "combined drug" using sub-optimal doses of methylphenidate, atomoxetine, and fluoxetine and investigated the combined treatment effects in MK-801-treated mice. No sub-optimal dose monotherapy alleviated ADHD behavioral condition in MK-801-treated mice. However, treatment with the combined drug attenuated the impaired behavior of MK-801-treated animals. Growth impediment, sleep disturbances, or risk of substance abuse were not observed in mice treated subchronically with the combined drugs. Finally, we observed that the combined ADHD drug rescued alterations in p-AKT and p-ERK1/2 levels in the prefrontal cortex and hippocampus, respectively, of MK-801-treated mice. Our results provide experimental evidence of a possible new pharmacotherapy option in ameliorating the ADHD behavioral condition without the expected adverse effects. The detailed mechanism of action underlying the synergistic therapeutic efficacy and reduced adverse reaction by combinatorial drug treatment should be investigated further in future studies.

1MeTIQ and olanzapine, despite their neurochemical impact, did not ameliorate performance in fear conditioning and social interaction tests in an MK-801 rat model of schizophrenia.

BACKGROUND: The aim of the present study was to evaluate the effect of 1MeTIQ on fear memory and social interaction in an MK-801-induced model of schizophrenia. The results obtained after administration of 1MeTIQ were compared with those obtained with olanzapine, an antipsychotic drug. METHODS: Sprague-Dawley rats received a single injection of MK-801 to induce behavioral disorders. 1MeTIQ was given either acutely in a single dose or chronically for 7 consecutive days. Olanzapine was administered once. In groups receiving combined treatments, 1MeTIQ or olanzapine was administered 20 min before MK-801 injection. Contextual fear conditioning was used to assess disturbances in fear memory (FM), and the sociability of the rats was measured in the social interaction test (SIT). Biochemical analysis was carried out to evaluate monoamine levels in selected brain structures after treatment. RESULTS: Our results are focused mainly on data obtained from neurochemical studies, demonstrating that 1MeTIQ inhibited the MK-801-induced reduction in dopamine levels in the frontal cortex and increased the 5-HT concentration. The behavioral tests revealed that acute administration of MK-801 caused disturbances in both the FM and SIT tests, while neither 1MeTIQ nor olanzapine reversed these deficits. CONCLUSION: 1MeTIQ, although pharmacologically effective (i.e., it reverses MK-801-induced changes in monoamine activity), did not influence MK-801-induced social and cognitive deficits. Thus, our FM tests and SIT did not support the main pharmacological hypotheses that focus on dopamine system stabilization and dopamine-serotonin system interactions as probable mechanisms for inhibiting the negative symptoms of schizophrenia.

Fluoxetine attenuates prepulse inhibition deficit induced by neonatal administration of MK-801 in mice.

Increasing evidence supports schizophrenia may be a neurodevelopmental and neurodegenerative disorder. Fluoxetine, a selective serotonin reuptake inhibitor, has been reported to have neuroprotective effects and be effective in treating neurodegenerative disorders including schizophrenia. The objective of the present study was to evaluate the effect and underlying neuroprotective mechanism of fluoxetine on the sensorimotor gating deficit, a schizophrenia-like behavior in a neurodevelopmental schizophrenic mouse model induced by MK-801, an N-methyl-D-aspartate glutamate receptor antagonist. On postnatal day 7, mouse pups were treated with a total seven subcutaneous daily injections of MK-801 (1 mg/kg/day), followed by intraperitoneal injection of fluoxetine (5 or 10 mg/kg/day) starting on postnatal day 14 in the MK-801-injected mice for 4 weeks. The sensorimotor gating deficit in mice was measured by prepulse inhibition (PPI) behavioral test on postnatal day 43. After the behavioral test, the protein expression of brain-derived neurotrophic factor (BDNF) was measured by western blot or ELISA in the frontal cortex of mice. Our results showed fluoxetine attenuated PPI deficit and the decrease of cerebral BDNF expression in the MK-801-injected mice. These results suggest that fluoxetine can be used to treat sensorimotor gating deficit in a neurodevelopmental mouse model of schizophrenia, and the attenuating effect of fluoxetine on sensorimotor gating deficit may be related to fluoxetine's neuroprotective effect targeting on the modulation of cerebral BDNF.

Clozapine Improves Behavioral and Biochemical Outcomes in a MK-801-Induced Mouse Model of Schizophrenia.

Glutamatergic N-methyl-D-aspartate (NMDA) receptors have critical roles in several neurological and psychiatric diseases. Dizocilpine (MK-801) is a ligand at phencyclidine recognition sites that is associated with NMDA receptor-coupled cation channels, where it acts as a potent noncompetitive antagonist of central glutamate receptors. In this study, we investigate the effect of clozapine on MK-801-induced neurochemical and neurobehavioral alterations in the prefrontal cortex of mice. Acute administration of NMDA noncompetitive antagonist MK-801 impairs motor coordination, grip strength, and locomotor activity. Clozapine is the only medication that is indicated for treating refractory schizophrenia, due to its superior efficacy among all antipsychotic agents; however, its mechanism is not well understood. To understand its mechanism, we investigated the effects of clozapine on motor coordination, locomotor activity, and grip strength in mice against the NMDA receptor antagonist MK-801. MK-801 induced elevations in acetylcholinesterase (AChE) activity, monoamine oxidase (MAO) activity, and c-fos expression. The administration of clozapine inhibited the effects caused by MK-801 (0.2 mg/kg body weight). Motor coordination and grip strength paradigms that had been altered by MK-801 were restored by clozapine. Moreover, clozapine also ameliorated MK-801-induced elevation in AChE and MAO activity. Our immunostaining results demonstrated that clozapine treatment reduced overexpression of the neuronal activity marker c-fos in cortices of the brain. Results of the current study determine that clozapine ameliorated cognition in MK-801-treated mice via cholinergic and neural mechanisms. These findings show that clozapine possesses the potential to augment cognition in diseases such as schizophrenia.

Metformin attenuates antipsychotic-induced metabolic dysfunctions in MK801-induced schizophrenia-like rats.

RATIONALE: Second-generation antipsychotics are the first-line medications prescribed for schizophrenic patients; however, some of them, such as olanzapine and risperidone, may induce metabolic dysfunctions during short-term treatment. Metformin is an effective adjuvant that attenuates antipsychotic-induced metabolic dysfunctions (AIMD) in clinical practice. Whether metformin can reverse AIMD and whether metformin affects the therapeutic effects of antipsychotics in animal models of schizophrenia are questions that still need to be investigated. METHODS: In this study, an animal model of schizophrenia was established by consecutive injections of MK801 during the neurodevelopmental period. In adulthood, different dosages of olanzapine or risperidone treatment were administered to the schizophrenia model animals for 14 days. Both therapeutic effects and metabolic adverse effects were measured by behavioral tests, histopathological tests, and biochemical tests. The coadministration of different doses of metformin with olanzapine or risperidone was used to evaluate the effects of metformin on both AIMD and the therapeutic effect of those antipsychotics. RESULTS: The MK801-treated rats showed schizophrenia-like behavior and variations in the shape and volume of the hippocampus. Both olanzapine and risperidone reversed the MK801-induced behavioral abnormalities as the dosage increased; however, they degenerated the hepatocytes in the liver and influenced the blood lipid levels and blood glucose levels. The coadministration of metformin did not affect the therapeutic effects of olanzapine or risperidone on behavioral abnormalities but attenuated the metabolic dysfunctions induced by those antipsychotics. CONCLUSION: Metformin attenuated the olanzapine- and risperidone-induced metabolic dysfunctions in MK801-induced schizophrenia-like rats without reducing the therapeutic effects of the antipsychotics.

ω-3PUFAs Improve Cognitive Impairments Through Ser133 Phosphorylation of CREB Upregulating BDNF/TrkB Signal in Schizophrenia.

Schizophrenia (SZ) is a serious mental condition and is associated with cognitive impairments. Brain-derived neurotrophic factor (BDNF) is one of the learning- and memory-related molecules found in the CNS and its level was reported to be reduced in SZ brain, while ω-3 polyunsaturated fatty acids (ω-3PUFAs) could improve SZ symptoms, but its mechanism of action remains unknown. Using MK801 injection-induced SZ rat model, we here found that supplementation with ω-3PUFAs improved the levels of p-CREB, BDNF, and p-TrkB in the brain of SZ rats, and restore hippocampal neuronal damage, thereby reducing cognitive impairments in SZ rats. However, overexpression of AAV9/CREB S133A (CREB inactivated mutation) downregulated BDNF/TrkB signaling pathway and remarkably abolished the preventive effect of ω-3PUFAs in MK801-induced schizophrenia. Interestingly, AAV9/CREB S133D (CREB activated mutation) improved synaptic dysfunctions and cognitive defects in MK801 rats. In conclusion, these findings indicate that MK801-induced SZ lesions dephosphorylate CREB at Ser133 site, leading to neuron damage, and ω-3PUFAs improve SZ cognitive impairments by upregulating the CREB/BDNF/TrkB pathway, which provides new clues for the mechanism of SZ cognitive impairments, and a basis for therapeutic intervention.

Retrograde and anterograde contextual fear amnesia induced by selective elimination of layer IV-Va neurons in the granular retrosplenial cortex (A29).

Differences in cytoarchitectural organization and connectivity distinguishes granular (or area 29, A29) and dysgranular (or area 30, A30) subdivisions of the retrosplenial cortex (RSC). Although increasing evidence supports the participation of RSC in contextual fear learning and memory, the contribution of each RSC subdivision remains unknown. Here we used orchiectomized rats and intraperitoneal (i.p.) injections of saline (control) or 5 mg/kg MK801, to trigger selective degeneration of pyramidal neurons in layers IV-Va of A29 (A29MK801 neurons). These treatments were applied 3 days before or two days after contextual fear conditioning, and contextual fear memory was evaluated by scoring freezing in the conditioned context five days after training. Afterwards, brains were fixed and c-Fos and Egr-1 expression were assessed as surrogates of neuronal activity elicited by the recall in A29, A30 and in limbic areas. We found that eliminating A29MK801 neurons after training reduces conditioned freezing to 43.1 ± 9.9% respect to control rats. This was associated with a significant reduction of c-Fos and Egr-1 expression in A30, but not in other limbic areas. On the other hand, eliminating A29MK801 neurons before training caused a mild but significant reduction of conditioned freezing to 79.7 ± 6.8%, which was associated to enhanced expression of c-Fos in A29, A30 and CA1 field of hippocampus, while Egr-1 expression in caudomedial (CEnt) entorhinal cortex was not depressed as in control animals. These observations show that severeness of amnesia differs according to whether A29MK801 neurons were eliminated before or after conditioning, likely because loss of A29MK801 neurons after conditioning disrupt memory engram while their elimination before training allow recruitment of other neurons in A29 for partial compensation of contextual fear learning and memory. These observations add further support for the critical role of A29MK801 neurons in contextual fear learning and memory by connecting limbic structures with A30.

Neuroprotective role of taurine on MK-801-induced memory impairment and hyperlocomotion in zebrafish.

Schizophrenia is a neuropsychiatric condition that reaches around 1% of people worldwide. Because taurine exerts a neuroprotective role in the brain, this molecule is a promising candidate to reduce schizophrenia-like symptoms. Here, we investigated a possible neuroprotective role of taurine against MK-801-induced memory deficit and hyperlocomotion in zebrafish using the inhibitory avoidance task and the novel tank diving test, respectively. First, we assessed the influence of different MK-801 doses (0.1, 0.3, 0.5, 1 and 2 mg/kg, i.p.) on memory consolidation. Although all MK-801 doses tend to reduce the retention index, only 2 mg/kg MK-801 showed robust amnesic effects. Then, we evaluated whether taurine pretreatments (42, 150 and 400 mg/L for 60 min) prevent MK-801-induced cognitive impairment. Immediately after the training, animals were exposed to non-chlorinated water or taurine and subsequently challenged with 2 mg/kg MK-801, i.p. The test session was performed 24 h after training. Although taurine alone did not change memory retention when compared with control, taurine pretreatments prevented MK-801-induced memory deficit. Importantly, no locomotor changes were observed 24 h after the training session. In the novel tank diving test, MK-801 induced hyperlocomotion and disrupted vertical activity, while 400 mg/L taurine pretreatment prevented these effects. Overall, our novel findings indicate a neuroprotective role of taurine against MK-801-induced memory deficit and hyperlocomotion, reinforcing the growing utility of zebrafish models to investigate the beneficial effects of different compounds against glutamate excitotoxicity.

Effects of beta-hydroxybutyrate administration on MK-801-induced schizophrenia-like behaviour in mice.

RATIONALE: Impaired cerebral glucose metabolism is a core pathological feature of schizophrenia. We recently demonstrated that a ketogenic diet, causing a shift from glycolysis to ketosis, normalized schizophrenia-like behaviours in an acute N-methyl-D-aspartate (NMDA) receptor antagonist model of the illness. Ketogenic diet produces the ketone body, ß-hydroxybutyrate (BHB), which may serve as an alternative fuel source in its own right without a strict dietary regime. OBJECTIVE: We hypothesized that chronic administration of BHB replicates the therapeutic effects of ketogenic diet in an acute NMDA receptor hypofunction model of schizophrenia in mice. METHODS: C57Bl/6 mice were either treated with acute doses of 2 mmol/kg, 10 mmol/kg, or 20 mmol/kg BHB or received daily intraperitoneal injections of 2 mmol/kg BHB or saline for 3 weeks. Behavioural testing assessed the effect of acute challenge with 0.2 mg/kg MK-801 or saline on open field behaviour, social interaction, and prepulse inhibition of startle (PPI). RESULTS: Acute BHB administration dose-dependently increased BHB plasma levels, whereas the 2 mmol/kg dose increased plasma glucose levels. The highest acute dose of BHB supressed spontaneous locomotor activity, MK-801-induced locomotor hyperactivity and MK-801-induced disruption of PPI. Chronic BHB treatment normalized MK-801-induced hyperlocomotion, reduction of sociability, and disruption of PPI. CONCLUSION: In conclusion, BHB may present a novel treatment option for patients with schizophrenia by providing an alternative fuel source to normalize impaired glucose metabolism in the brain.

The protective effects of Mogroside V and its metabolite 11-oxo-mogrol of intestinal microbiota against MK801-induced neuronal damages.

RATIONALE: Animal models, notably with non-competitive NMDA receptor antagonist MK801, are commonly used to investigate the mechanisms of schizophrenia and to pursue its mechanism-related drug discoveries. OBJECTIVES: In the current study, we have extensively examined the protective effects of MogrosideV (MogV), a plant-derived three terpene glucoside known to exhibit anti-oxidative and anti-inflammatory activities. METHODS AND RESULTS: Here, we investigated its protective effects against neuronal damages elicited by MK-801 treatment. Our behavioral experimental results showed that MK-801-induced PPI deficits and social withdrawal were prevented by MogV treatment. Moreover, the cellular and neurochemical responses of MK-801 in medial prefrontal cortical cortex (mPFC) were also ameliorated by MogV treatment. Also, profiling metabolites assay through artificial intestinal microbiota was performed to identify bioactive components of MogV. An in vitro study of primary neuronal culture demonstrated that MogV and its metabolite 11-oxo-mogrol treatment prevented the MK-801-induced neuronal damages through the mechanisms of promoting neurite outgrowth, inhibiting cell apoptosis, and [Ca2+]i release. Additionally, 11-oxo-mogrol reversed inactivation of phosphorylation levels of AKT and mTOR induced by MK801. CONCLUSIONS: These results suggest therapeutic potential of MogV for schizophrenia.

Subchronic MK-801 treatment during adolescence induces long-term, not permanent, excitatory-inhibitory imbalance in the rat hippocampus.

Adolescence is a critical neurodevelopmental period for both excitatory and inhibitory (E/I) neurotransmission and often witnesses the typical onsets of schizophrenia. One possibility is that disruptions in adolescent neurodevelopmental processes may produce schizophrenia-like behavioral and neurobiological abnormalities. We previously reported that subchronic treatment of adolescent animals with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 induced cognitive deficits and reduced interneuron densities in rat medial prefrontal cortex, and these changes persisted one week after MK-801 exposure. However, it remains unclear how this treatment may affect E/I balance in hippocampus, which has long been associated with the pathophysiology of schizophrenia. Here, we examined hippocampal E/I biomarkers in adolescent rats treated with MK-801 (0.2 mg/kg, i.p., 14 days) and found increases in the ratio of the expression levels of vesicular glutamate transporter-1 (VGluT1) and vesicular gamma-aminobutyric acid (GABA) transporter (VGAT) 24 h and 7 days after MK-801 exposure. Interestingly, the increased VGluT1/VGAT ratio at the two time points was driven by upregulated VGluT1 expression and downregulated VGAT expression, respectively. The decrease in VGAT expression persisted 14 days after MK-801 exposure and recovered two weeks later. No alterations in hippocampal interneuron densities were observed. Behaviorally, the treatment decreased prepulse inhibition at 24 h but not 14 days, after MK-801 exposure. Taken together, these results demonstrate that subchronic NMDA receptor blockade during adolescence induces long-term, but not permanent, E/I imbalance in the rat hippocampus, which could be attributed to the dysregulation of glutamatergic transmission in the short term and of GABAergic transmission in the long term.

Simultaneous activation of mGlu2 and muscarinic receptors reverses MK-801-induced cognitive decline in rodents.

The activity of an allosteric agonist of muscarinic M1 receptor, VU0357017, and a positive allosteric modulator (PAM) of M5 receptor, VU0238429, were investigated alone or in combination with the mGlu2 receptor PAM, LY487379 using the following behavioural tests: prepulse inhibition (PPI), novel object recognition (NOR), and spatial delayed alternation (SDA). VU0357017 (10 and 20 mg/kg) and VU0238429 (5 and 10 mg/kg) reversed deficits in PPI while VU0238429 (2.5 and 5 mg/kg) was effective in SDA. The simultaneous administration of subeffective doses of M1 or M5 activators (5, 1, or 0.25 mg/kg) with LY487379 (0.5 mg/kg) induced the same effect as that observed for the active dose of each compound. Selective M1 or M5 receptor blockers antagonized the effect exerted by these combinations, and pharmacokinetic studies confirmed independent transport through the blood-brain barrier. The expression of both receptors (M1 and M5) was established in brain structures involved in cognition (neocortex, hippocampus, and entorhinal cortex) in both the rat and the mouse brains by immunofluorescence staining. Specifically, double neuronal staining of mGlu2-M1 and mGlu2-M5 receptors was observed in many areas of the rat brain, while the number of double-stained mGlu2-M1 receptors was moderate in the mouse brain with no mGlu2-M5 colocalization. Finally, the combined administration of subeffective doses of the compounds did not alter prolactin levels or motor coordination, in contrast to the compounds given alone at the highest dose or in combination with standard neuroleptics.

Intracellular mechanisms and behavioral changes in mouse model of attention deficit hyperactivity disorder: Importance of age-specific NMDA receptor blockade.

Exposure of NMDA receptor antagonists during developmental stages leads to behavioral consequences like attention deficit hyperactivity disorder (ADHD). However, the underlying molecular mechanisms have remained poorly understood. Herein, we studied the phosphorylated Akt (pAkt) and caspase-3, the key regulators of neuronal cell survival/death, as the probable downstream targets of MK-801 often used to engender ADHD-like condition. Swiss albino mice at postnatal days (PND) 7, 14 or 21 were injected with a single dose of MK-801 and evaluated for hyperactivity (open field test) and memory deficit at adolescence (PND 30) and adult stages (PND 60). PND 7 or 14 treatment groups (but not PND 21) consistently showed hyperactivity at the adolescence stage. A significant increase in working and reference memory errors in radial arm maze was noted at the adolescence age. PND 7 group continued to display the symptoms even in adulthood. All the treatment groups showed a significant decrease in the percent alterations (Y-maze) and discrimination index (novel object recognition test) at adolescence age. A significant increase in caspase-3 expression was noted in the prefrontal cortex (PFC) and hippocampus, whereas increased pAkt was noticed only in the hippocampus, following a single injection of MK-801 at PND 7. Concurrently, PND 7 treatment group showed significantly decreased neuronal nuclei (NeuN) expression (a marker for mature neurons) in the dentate gyrus, cornu ammonis-3 and PFC, but not in cornu ammonis-1, at adolescence age. We suggest that the observed symptoms of ADHD at adolescence and adulthood stages may be linked to alteration in pAkt and caspase-3 followed MK-801 treatment at PND 7.

The mGluR2/3 agonist LY379268 reverses NMDA receptor antagonist effects on cortical gamma oscillations and phase coherence, but not working memory impairments, in mice.

BACKGROUND: Abnormalities in neural oscillations that occur in the gamma frequency range (30-80 Hz) may underlie cognitive deficits in schizophrenia. Both cognitive impairments and gamma oscillatory disturbances can be induced in healthy people and rodents by administration of N-methyl-D-aspartate receptor (NMDAr) antagonists. AIMS: We studied relationships between cognitive impairment and gamma abnormalities following NMDAr antagonism, and attempted to reverse deficits with the metabotropic glutamate receptor type 2/3 (mGluR2/3) agonist LY379268. METHODS: C57/Bl6 mice were trained to perform the Trial-Unique Nonmatching to Location (TUNL) touchscreen test for working memory. They were then implanted with local field potential (LFP) recording electrodes in prefrontal cortex and dorsal hippocampus. Mice were administered either LY379268 (3 mg/kg) or vehicle followed by the NMDAr antagonist MK-801 (0.3 or 1 mg/kg) or vehicle prior to testing on the TUNL task, or recording LFPs during the presentation of an auditory stimulus. RESULTS: MK-801 impaired working memory and increased perseveration, but these behaviours were not improved by LY379268 treatment. MK-81 increased the power of ongoing gamma and high gamma (130-180 Hz) oscillations in both brain regions and regional coherence between regions, and these signatures were augmented by LY379268. However, auditory-evoked gamma oscillation deficits caused by MK-801 were not affected by LY379268 pretreatment. CONCLUSIONS: NMDA receptor antagonism impairs working memory in mice, but this is not reversed by stimulation of mGluR2/3. Since elevations in ongoing gamma power and regional coherence caused by MK-801 were improved by LY379268, it appears unlikely that these specific oscillatory abnormalities underlie the working memory impairment caused by NMDAr antagonism.