Chronic MK-801 Application in Adolescence and Early Adulthood: A Spatial Working Memory Deficit in Adult Long-Evans Rats But No Changes in the Hippocampal NMDA Receptor Subunits

Behavioral and transcriptional effects of repeated electroconvulsive seizures in the neonatal MK-801-treated rat model of schizophrenia

RATIONALE

Electroconvulsive therapy (ECT) is an effective treatment modality for schizophrenia. However, its antipsychotic-like mechanism remains unclear.

OBJECTIVES

To gain insight into the antipsychotic-like actions of ECT, this study investigated how repeated treatments of electroconvulsive seizure (ECS), an animal model for ECT, affect the behavioral and transcriptomic profile of a neurodevelopmental animal model of schizophrenia.

METHODS

Two injections of MK-801 or saline were administered to rats on postnatal day 7 (PN7), and either repeated ECS treatments (E10X) or sham shock was conducted daily from PN50 to PN59. Ultimately, the rats were divided into vehicle/sham (V/S), MK-801/sham (M/S), vehicle/ECS (V/E), and MK-801/ECS (M/E) groups. On PN59, prepulse inhibition and locomotor activity were tested. Prefrontal cortex transcriptomes were analyzed with mRNA sequencing and network and pathway analyses, and quantitative real-time polymerase chain reaction (qPCR) analyses were subsequently conducted.

RESULTS

Prepulse inhibition deficit was induced by MK-801 and normalized by E10X. In M/S vs. M/E model, Egr1, Mmp9, and S100a6 were identified as center genes, and interleukin-17 (IL-17), nuclear factor kappa B (NF-κB), and tumor necrosis factor (TNF) signaling pathways were identified as the three most relevant pathways. In the V/E vs. V/S model, mitophagy, NF-κB, and receptor for advanced glycation end products (RAGE) pathways were identified. qPCR analyses demonstrated that Igfbp6, Btf3, Cox6a2, and H2az1 were downregulated in M/S and upregulated in M/E.

CONCLUSIONS

E10X reverses the behavioral changes induced by MK-801 and produces transcriptional changes in inflammatory, insulin, and mitophagy pathways, which provide mechanistic insight into the antipsychotic-like mechanism of ECT.

MK-801 and cognitive functions: Investigating the behavioral effects of a non-competitive NMDA receptor antagonist

RATIONALE

MK-801 (dizocilpine) is a non-competitive NMDA receptor antagonist originally explored for anticonvulsant potential. Despite its original purpose, its amnestic properties led to the development of pivotal models of various cognitive impairments widely employed in research and greatly impacting scientific progress. MK-801 offers several advantages; however, it also presents drawbacks, including inducing dose-dependent hyperlocomotion or ambiguous effects on anxiety, which can impact the interpretation of behavioral research results.

OBJECTIVES

The present review attempts to summarize and discuss the effects of MK-801 on different types of memory and cognitive functions in animal studies.

RESULTS

A plethora of behavioral research suggests that MK-801 can detrimentally impact cognitive functions. The specific effect of this compound is influenced by variables including developmental stage, gender, species, strain, and, crucially, the administered dose. Notably, when considering the undesirable effects of MK-801, doses up to 0.1 mg/kg were found not to induce stereotypy or hyperlocomotion.

CONCLUSION

Dizocilpine continues to be of significant importance in preclinical research, facilitating the exploration of various procognitive therapeutic agents. However, given its potential undesirable effects, it is imperative to meticulously determine the appropriate dosages and conduct supplementary evaluations for any undesirable outcomes, which could complicate the interpretation of the findings.

Tailoring Risperidone-Loaded Glycethosomal In Situ Gels Using Box-Behnken Design for Treatment of Schizophrenia-Induced Rats via Intranasal Route

Schizophrenic patients often face challenges with adherence to oral regimens. The study aimed to highlight the potentiality of intranasal ethanol/glycerin-containing lipid-nanovesicles (glycethosomes) incorporated into in situ gels for sustaining anti-psychotic risperidone (RS) release. The Box-Behnken Design (BBD) was followed for in vitro characterization. Glycethosomal-based in situ gels were examined by physical, ex vivo, and in vivo investigations. The ethanol impact on minimizing the vesicle size (VS) and enhancing the zeta potential (ZP) and entrapment efficiency (EE%) of nanovesicles was observed. Glycerin displayed positive action on increasing VS and ZP of nanovesicles, but reduced their EE%. After incorporation into various mucoadhesive agent-enriched poloxamer 407 (P407) in situ gels, the optimized gel containing 20% P407 and 1% hydroxypropyl methyl cellulose-K4M (HPMC-K4M) at a 4:1 gel/glycethosomes ratio showed low viscosity and high spreadability with acceptable pH, gel strength, and mucoadhesive strength ranges. The ethanol/glycerin mixture demonstrated a desirable ex vivo skin permeability of RS through the nasal mucosa. By pharmacokinetic analysis, the optimized gel showed eight-fold and three-fold greater increases in RS bioavailability than the control gel and marketed tablet, respectively. Following biochemical assessments of schizophrenia-induced rats, the optimized gel boosted the neuroprotective, anti-oxidant, and anti-inflammatory action of RS in comparison to other tested preparations. Collectively, the intranasal RS-loaded glycethosomal gel offered a potential substitute to oral therapy for schizophrenic patients.

Repeated dextromethorphan administration in adolescent rats produces long-lasting behavioral alterations

Initiation of non-medical dextromethorphan (DXM) use often occurs in adolescence, yet little is known about the consequences when use begins during this developmental period. The current experiments examined the acute response and the effects of repeated exposure to DXM in adolescence on behavior in adulthood. We examined locomotor activity, locomotor sensitization, and cognitive function, in rats that received repeated administration of DXM. Groups of adolescent (PND 30) and adult (PND 60) male rats were treated with DXM (60 mg/kg) once daily for 10 days. Locomotor activity in response to DXM was assessed following the first injection, on the 10th day of injection (adolescent - PND 39; adult - PND 69), and following 20 days of abstinence (adolescent - PND 60; adult - PND 90). Acute locomotor effects and locomotor sensitization were compared in adolescents and adults; cross-sensitization to ketamine, another dissociative with abuse potential, was also examined. In a separate group of rodents cognitive deficits were assessed following a 20 day abstinence period (adolescent - PND 60; adult - PND 90) in spatial learning and novel object recognition tasks. The locomotor stimulant effect of DXM was much greater in adolescents than adults. Also, only adolescent rats that were repeatedly administered DXM demonstrated locomotor sensitization at the end of 10 days of injection. However, sensitization occurred after the abstinence period in all rats regardless of age. Nonetheless, cross-sensitization to ketamine was only evident in adolescent-treated rats. DXM also led to an increase in perseverative errors in reversal learning only in the adolescent-treated group. We conclude that repeated use of DXM produces long-lasting neuroadaptations that may contribute to addiction. Deficits in cognitive flexibility occur in adolescents, although further work is necessary to confirm these findings. The results extend the understanding of potential long-term consequences of DXM use in adolescents and adults.

Receptor-Mediated AKT/PI3K Signalling and Behavioural Alterations in Zebrafish Larvae Reveal Association between Schizophrenia and Opioid Use Disorder

The link between substance abuse and the development of schizophrenia remains elusive. In this study, we assessed the molecular and behavioural alterations associated with schizophrenia, opioid addiction, and opioid withdrawal using zebrafish as a biological model. Larvae of 2 days post fertilization (dpf) were exposed to domperidone (DMP), a dopamine-D2 dopamine D2 receptor antagonist, and morphine for 3 days and 10 days, respectively. MK801, an N-methyl-D-aspartate (NMDA) receptor antagonist, served as a positive control to mimic schizophrenia-like behaviour. The withdrawal syndrome was assessed 5 days after the termination of morphine treatment. The expressions of schizophrenia susceptibility genes, i.e., pi3k, akt1, slc6a4, creb1 and adamts2, in brains were quantified, and the levels of whole-body cyclic adenosine monophosphate (cAMP), serotonin and cortisol were measured. The aggressiveness of larvae was observed using the mirror biting test. After the short-term treatment with DMP and morphine, all studied genes were not differentially expressed. As for the long-term exposure, akt1 was downregulated by DMP and morphine. Downregulation of pi3k and slc6a4 was observed in the morphine-treated larvae, whereas creb1 and adamts2 were upregulated by DMP. The levels of cAMP and cortisol were elevated after 3 days, whereas significant increases were observed in all of the biochemical tests after 10 days. Compared to controls, increased aggression was observed in the DMP-, but not morphine-, treated group. These two groups showed reduction in aggressiveness when drug exposure was prolonged. Both the short- and long-term morphine withdrawal groups showed downregulation in all genes examined except creb1, suggesting dysregulated reward circuitry function. These results suggest that biochemical and behavioural alterations in schizophrenia-like symptoms and opioid dependence could be controlled by common mechanisms.

Differential expression of miR-148b, miR-129-2 and miR-296 in animal models of schizophrenia-Relevance to NMDA receptor hypofunction

Hypofunction of N-methyl-d-aspartate receptors (NMDAR) is a key component in the pathophysiology of schizophrenia. Alterations in the regulation of NMDARs by microRNAs (miRNAs) are possible since numerous miRNAs are differentially expressed in post mortem schizophrenia brain samples. We screened the miRNAs that are altered in schizophrenia against the targets, Grin2A and Grin2B subunits of NMDAR using bioinformatic tools. Among the predicted miRNAs some interacted with the 3'-UTR sequences of Grin2A (miR-296, miR-148b, miR-129-2, miR-137) and Grin2B (miR-296, miR-148b, miR-129-2, miR-223) in dual luciferase assays. This was supported by downregulation of the GluN2B protein in primary hippocampal neurons upon overexpressing Grin2B targeting miRNAs. In two models of schizophrenia-pharmacological MK-801 model and neurodevelopmental methylazoxymethanol acetate (MAM) model which showed cognitive deficits - protein levels of GluN2A and GluN2B were downregulated but their transcript levels were upregulated. miR-296-3p, miR-148b-5p and miR-137 levels showed upregulation in both models which could have interacted with Grin2A/Grin2B transcripts resulting in translational arrest. In MAM model, reciprocal changes in the expression of the 3p and 5p forms of miR-148b and miR-137 were observed. Expression of some genes implicated in schizophrenia such as Neuregulin 1 (NRG1), BDNF and CaMKIIα, were also altered in these models. This is the first report showing downregulation of GluN2A and GluN2B by miR-296, miR-148b and miR-129-2 in vitro and association between them in animal models. Mining miRNAs regulating NMDA receptors might give insights into the pathophysiology of this disorder, providing avenues in therapeutics.

CBD Effects on Motor Profile and Neurobiological Indices Related to Glutamatergic Function Induced by Repeated Ketamine Pre-Administration

Clinical evidence and experimental studies have shown the psychotomimetic properties induced by ketamine. Moreover, acute or chronic ketamine (KET) administration has been widely used for modeling schizophrenia-like symptomatology and pathophysiology. Several studies have reported the antipsychotic potential of cannabidiol (CBD), while there is limited information on the cannabidiol effect on KET-induced schizophrenia-like impairments. Therefore, the goal of the present study was to evaluate neuroplastic changes induced by repeated KET administration, which is used as an experimental model of schizophrenia—with a behavioral focus on positive-like symptomatology– and to assess the modulatory role of CBD treatment. The present findings have shown a robust increase in motor activity in KET-treated rats, following a 10-day period of chronic administration at the sub-anesthetic dose of 30 mg/kg (i.p), that was reversed to normal by subsequent chronic CBD treatment. Concerning the expression of glutamate receptors, the current findings have shown region-dependent KET-induced constitutional alterations in NMDA and AMPA receptors that were modified by subsequent CBD treatment. Additionally, repeated KET administration increased ERK1/2 phosphorylation state in all regions examined, apart from the ventral hippocampus that was modulated by subsequent CBD treatment. The present results show, for the first time, a stimulated motor output coupled with a specific glutamatergic-related status and ERK1/2 activation following chronic KET administration that were attenuated by CBD treatment, in a region-dependent manner. These findings provide novel information concerning the antipsychotic potential of CBD using a specific design of chronic KET administration, thus contributing to experimental approaches that mirror the symptomatology and pathophysiology of schizophrenia.

Evaluation of acute and chronic nociception in subchronically administered MK-801-induced rat model of schizophrenia

Patients diagnosed with schizophrenia have been reported to exhibit atypically low pain sensitivity and to vary in their experience of chronic pain. To the best of our knowledge, there has yet to be an animal study that provides information concerning the relationship between models of schizophrenia and pain. In the present study, we investigated several distinct nociceptive behaviors in a translational rat model of schizophrenia (0. 5 mg/kg MK-801, twice a day for 7 days followed by a 7-day washout period). The presence of the expected cognitive deficit was confirmed with novel object recognition (NOR) paradigm prior to nociception testing. MK-801-treated rats with lack of novelty interest in NOR testing showed: hyposensitivity to thermal and mechanical stimuli; short-term hypoalgesia followed by augmented hyperalgesia in response to formalin-induced spontaneous nociception and increased thermal and mechanical hyperalgesia in the complete Freund's adjuvant (CFA) induced chronic pain model. In conclusion, MK-801 induced antinociception effects for thermal stimuli in rats that were consistent with the decreased pain sensitivity observed in schizophrenia patients. Additionally, the amplified biphasic response exhibited by the MK-801 group in the formalin-induced spontaneous nociception test affirms the suitability of the test as a model of acute to delayed pain transition.

Schizophrenia, the gut microbiota, and new opportunities from optogenetic manipulations of the gut-brain axis

Schizophrenia research arose in the twentieth century and is currently rapidly developing, focusing on many parallel research pathways and evaluating various concepts of disease etiology. Today, we have relatively good knowledge about the generation of positive and negative symptoms in patients with schizophrenia. However, the neural basis and pathophysiology of schizophrenia, especially cognitive symptoms, are still poorly understood. Finding new methods to uncover the physiological basis of the mental inabilities related to schizophrenia is an urgent task for modern neuroscience because of the lack of specific therapies for cognitive deficits in the disease. Researchers have begun investigating functional crosstalk between NMDARs and GABAergic neurons associated with schizophrenia at different resolutions. In another direction, the gut microbiota is getting increasing interest from neuroscientists. Recent findings have highlighted the role of a gut-brain axis, with the gut microbiota playing a crucial role in several psychopathologies, including schizophrenia and autism.

There have also been investigations into potential therapies aimed at normalizing altered microbiota signaling to the enteric nervous system (ENS) and the central nervous system (CNS). Probiotics diets and fecal microbiota transplantation (FMT) are currently the most common therapies. Interestingly, in rodent models of binge feeding, optogenetic applications have been shown to affect gut colony sensitivity, thus increasing colonic transit. Here, we review recent findings on the gut microbiota–schizophrenia relationship using in vivo optogenetics. Moreover, we evaluate if manipulating actors in either the brain or the gut might improve potential treatment research. Such research and techniques will increase our knowledge of how the gut microbiota can manipulate GABA production, and therefore accompany changes in CNS GABAergic activity.

Behavioral Consequences of a Combination of Gad1 Haplodeficiency and Adolescent Exposure to an NMDA Receptor Antagonist in Long-Evans Rats

Glutamate decarboxylase 67-kDa isoform (GAD67), which is encoded by the GAD1 gene, is one of the key enzymes that produce GABA. The reduced expression of GAD67 has been linked to the pathophysiology of schizophrenia. Additionally, the excitatory glutamatergic system plays an important role in the development of this disorder. Animal model studies have revealed that chronic blockade of NMDA-type glutamate receptors can cause GABAergic dysfunction and long-lasting behavioral abnormalities. Based on these findings, we speculated that Gad1 haplodeficiency combined with chronic NMDA receptor blockade would lead to larger behavioral consequences relevant to schizophrenia in a rat model. In this study, we administered an NMDAR antagonist, MK-801 (0.2 mg/kg), to CRISPR/Cas9-generated Gad1^+/− rats during adolescence to test this hypothesis. The MK-801 treated Gad1^+/− rats showed a shorter duration in each rearing episode in the open field test than the saline-treated Gad1^+/+ rats. In contrast, immobility in the forced swim test was increased and fear extinction was impaired in Gad1^+/− rats irrespective of MK-801 treatment. Interestingly, the time spent in the center region of the elevated plus-maze was significantly affected only in the saline-treated Gad1^+/− rats. Additionally, the MK-801-induced impairment of the social novelty preference was not observed in Gad1^+/− rats. These results suggest that the synergistic and additive effects of Gad1 haplodeficiency and NMDA receptor blockade during adolescence on the pathogenesis of schizophrenia may be more limited than expected. Findings from this study also imply that these two factors mainly affect negative or affective symptoms, rather than positive symptoms.

NMDA receptors control development of somatosensory callosal axonal projections

Callosal projections from primary somatosensory cortex (S1) are key for processing somatosensory inputs and integrating sensory-motor information. How the callosal innervation pattern in S1 is formed during early postnatal development is not clear. We found that the normal termination pattern of these callosal projections is disrupted in cortex specific NMDAR mutants. Rather than projecting selectively to the primary/secondary somatosensory cortex (S1/S2) border, axons were uniformly distributed throughout S1. In addition, the density of this projection increased over postnatal life until the mice died by P30. By combining genetic and antibody-mediated loss of function, we demonstrated that it is GluN2B-containing NMDA receptors in target S1 that mediate this guidance phenotype, thus playing a central role in interhemispheric connectivity. Furthermore, we found that this function of NMDA receptors in callosal circuit formation is independent of ion channel function and works with the EPHRIN-B/EPHB system. Thus, NMDAR in target S1 cortex regulates the formation callosal circuits perhaps by modulating EPH-dependent repulsion.

Is Cannabidiol During Neurodevelopment a Promising Therapy for Schizophrenia and Autism Spectrum Disorders?

Schizophrenia and autism spectrum disorders (ASD) are psychiatric neurodevelopmental disorders that cause high levels of functional disabilities. Also, the currently available therapies for these disorders are limited. Therefore, the search for treatments that could be beneficial for the altered course of the neurodevelopment associated with these disorders is paramount. Preclinical and clinical evidence points to cannabidiol (CBD) as a promising strategy. In this review, we discuss clinical and preclinical studies on schizophrenia and ASD investigating the behavioral, molecular, and functional effects of chronic treatment with CBD (and with cannabidivarin for ASD) during neurodevelopment. In summary, the results point to CBD's beneficial potential for the progression of these disorders supporting further investigations to strengthen its use.

Enriched environment improves sevoflurane-induced cognitive impairment during late-pregnancy via hippocampal histone acetylation

Fetal exposure to sevoflurane induces long-term cognitive impairment. Histone acetylation regulates the transcription of genes involved in memory formation. We investigated whether sevoflurane exposure during late-pregnancy induces neurocognitive impairment in offspring, and if this is related to histone acetylation dysfunction. We determined whether the effects could be reversed by an enriched environment (EE). Pregnant rats were exposed to 2.5% sevoflurane or control for 1, 3, or 6 h on gestational day 18 (G18). Sevoflurane reduced brain-derived neurotrophic factor (BDNF), acetyl histone H3 (Ac-H3), and Ac-H4 levels and increased histone deacetylases-2 (HDAC2) and HDAC3 levels in the hippocampus of the offspring on postnatal day 1 (P1) and P35. Long-term potentiation was inhibited, and spatial learning and memory were impaired in the 6-h sevoflurane group at P35. EE alleviated sevoflurane-induced cognitive dysfunction and increased hippocampal BDNF, Ac-H3, and Ac-H4. Exposure to 2.5% sevoflurane for 3 h during late-pregnancy decreased hippocampal BDNF, Ac-H3, and Ac-H4 in the offspring but had no effect on cognitive function. However, when the exposure time was 6 h, impaired spatial learning and memory were linked to reduced BDNF, Ac-H3, and Ac-H4, which could be reversed by EE.

Evidence of Synaptic and Neurochemical Remodeling in the Retina of Aging Degus

Accumulation of amyloid-beta (Aβ) peptides is regarded as the hallmark of neurodegenerative alterations in the brain of Alzheimer’s disease (AD) patients. In the eye, accumulation of Aβ peptides has also been suggested to be a trigger of retinal neurodegenerative mechanisms. Some pathological aspects associated with Aβ levels in the brain are synaptic dysfunction, neurochemical remodeling and glial activation, but these changes have not been established in the retina of animals with Aβ accumulation. We have employed the Octodon degus in which Aβ peptides accumulated in the brain and retina as a function of age. This current study investigated microglial morphology, expression of PSD95, synaptophysin, Iba-1 and choline acetyltransferase (ChAT) in the retina of juvenile, young and adult degus using immunolabeling methods. Neurotransmitters glutamate and gamma-aminobutyric acid (GABA) were detected using immunogold labeling and glutamate receptor subunits were quantified using Western blotting. There was an age-related increase in presynaptic and a decrease in post-synaptic retinal proteins in the retinal plexiform layers. Immunolabeling showed changes in microglial morphology characteristic of intermediate stages of activation around the optic nerve head (ONH) and decreasing activation toward the peripheral retina. Neurotransmitter expression pattern changed at juvenile ages but was similar in adults. Collectively, the results suggest that microglial activation, synaptic remodeling and neurotransmitter changes may be consequent to, or parallel to Aβ peptide and phosphorylated tau accumulation in the retina.

Parvalbumin Interneuron Activation-Dependent Adult Hippocampal Neurogenesis Is Required for Treadmill Running to Reverse Schizophrenia-Like Phenotypes

Physical exercise can alleviate some of the schizophrenia symptoms in patients, the mechanisms, however, are still unclear. To investigate whether the GABAergic interneuron involved in the therapeutic effect of treadmill running on schizophrenia, the parvalbumin (PV)-positive GABAergic interneurons in the dentate gyrus (DG) was specifically activated or abolished and the effects were evaluated. In the MK801-induced schizophrenia-like animal model, we found:(1) Treadmill running rescued the schizophrenia-related behavioral phenotypes, promoted the adult hippocampal neurogenesis, and increased the dendrite number and complexity of newborn neurons. (2) Treadmill running increased the number of PV-positive interneurons in the DG; genetic ablation of these interneurons reduced adult neurogenesis and abolished the effect of treadmill running on the schizophrenia-related behaviors. Consistently, chemogenetic activation of these interneurons improved neurogenesis and alleviated the schizophrenia-related behaviors. These results suggest a pivotal role of PV-positive interneuron-mediated adult neurogenesis in exercise. (3) However, schizophrenia-related behavioral phenotypes and adult neurogenesis in the DG could still be reversed by exercise after specifically knocking out the schizophrenia-related gene ErbB4 in PV interneurons, as a means to reduce their GABA release. These results suggest that activation of PV interneurons in the DG is sufficient for treadmill running to reverse schizophrenia-like phenotypes.

Applying vinpocetine to reverse synaptic ultrastructure by regulating BDNF-related PSD-95 in alleviating schizophrenia-like deficits in rat

BACKGROUND

Schizophrenia is a mental disorder characterized by hyperlocomotion, cognitive symptoms, and social withdrawal. Brain-derived neurotrophic factor (BDNF) and postsynaptic density (PSD)-95 are related to schizophrenia-like deficits via regulating the synaptic ultrastructure, and play a role in drug therapy. Vinpocetine is a nootropic phosphodiesterase-1 (PDE-1) inhibitor that can reverse ketamine-induced schizophrenia-like deficits by increasing BDNF expression. However, the effects of vinpocetine on alleviating schizophrenia-like deficits via reversing the synaptic ultrastructure by regulating BDNF-related PSD-95 have not been sufficiently studied.

METHODS

In this study, the schizophrenic model was built using ketamine (30 mg/kg) for 14 consecutive days. The effect of vinpocetine on reversing schizophrenia-like behaviors was examined via behavioral testing followed by treatment with certain doses of vinpocetine (20 mg/kg, i.p.). The BDNF and PSD-95 levels in the posterior cingulate cortex (PCC) were measured using biochemical assessments. In addition, the synaptic ultrastructure was observed using transmission electron microscopy (TEM).

RESULTS

Ketamine induced drastic schizophrenia-like behaviors, lower protein levels of BDNF and PSD-95, and a change in the synaptic ultrastructure in the PCC. After treatment, the vinpocetine revealed a marked amendment in schizophrenia-like behaviors induced by ketamine, including higher locomotor behavior, lower cognitive behavior, and social withdrawal defects. Vinpocetine could increase the PSD-95 protein level by up-regulating the expression of BDNF. In addition, the synaptic ultrastructure was changed after vinpocetine administration, including a reduction in the thickness and curvature of the synaptic interface, as well as an increase in synaptic cleft width in the PCC.

CONCLUSION

Vinpocetine can reverse the synaptic ultrastructure by regulating BDNF-related PSD-95 to alleviate schizophrenia-like deficits induced by ketamine in rats.

Reversal of MK-801-Induced Disruptions in Social Interactions and Working Memory with Simultaneous Administration of LY487379 and VU152100 in Mice

Negative and cognitive symptoms of schizophrenia contribute to an impaired social and professional life for schizophrenic patients, and in most cases, these symptoms are treatment resistant. Therefore, identification of new treatment strategies is sorely needed. Metabotropic glutamate receptors (mGlu) and muscarinic (M) receptors for acetylcholine have been considered promising targets for novel antipsychotics. Among them, mGlu₂ and M₄ subtypes seem to be of particular importance. In the present study, the effect of mutual activation of mGlu₂ and M₄ receptors was assessed in MK-801-based animal models of negative and cognitive symptoms of schizophrenia, that is, social interaction and novel object recognition tests. Low sub-effective doses of LY487379 (0.5 mg/kg), a positive allosteric activator of the mGlu₂ receptor, and VU152100 (0.25−0.5 mg/kg), a positive allosteric modulator of the M₄ receptor, were simultaneously administered in the aforementioned tests. Combined administration of these compounds prevented MK-801-induced disturbances in social interactions and object recognition when acutely administered 30 min before MK-801. Prolonged (7 days) administration of these compounds resulted in the loss of effectiveness in preventing MK-801-induced disruptions in the novel object recognition test but not in the social interaction test. In the next set of experiments, MK-801 (0.3 mg/kg) was administered for seven consecutive days, and the activity of the compounds was investigated on day eight, during which time MK-801 was not administered. In this model, based on prolonged MK-801 administration, the effectiveness of the compounds to treat MK-801-induced disruptions was evident at low doses which were ineffective in preventing the behavioural disturbances induced by an acute MK-801 injection. Combined administration of the compounds did not exert better efficacy than each compound given alone. Pharmacokinetic analysis confirmed a lack of possible drug–drug interactions after combined administration of LY487379 and VU152100. Our data show that modulation of M₄ and mGlu₂ receptors may potentially be beneficial in the treatment of negative and cognitive symptoms of schizophrenia.

Metformin reverses the schizophrenia-like behaviors induced by MK-801 in rats

Schizophrenia is known to be a complex and disabling psychiatric disorder. Dopamine receptor antagonists have a significant therapeutic effect in improving the positive symptoms that are associated with the illness. Therefore, dopamine receptor antagonists are commonly used in the treatment of schizophrenia; however, they do not achieve satisfactory results in improving negative symptoms and cognitive impairment. Metformin, widely known as an antidiabetic drug, has been found to enhance spatial memory formation and improve anxiety-like behaviors in rodents. Metformin's neuroprotective effect has been well documented in several neurological disorders including Alzheimer's disease, Parkinson's disease, strokes, Huntington's disease, and seizures. In the present study, we used a rat model to explore the effect of metformin on schizophrenia-like behaviors induced by MK-801 (dizocilpine), an N-methyl-D-aspartate (NMDA) receptor antagonist. We found that the pre-pulse inhibition (PPI) deficit caused by MK-801 could be alleviated by metformin. The hyperlocomotion in the open field test induced by chronic treatment of MK-801 was reversed by administration of metformin. Metformin has no effect on the baseline level of anxiety in normal naive rats, while metformin could relieve the anxiety-like behaviors in MK-801-treatment rats, though this effect is not reaching a significant level. Additionally, metformin could significantly ameliorate working memory impairments induced by MK-801. Moreover, the increased level of phosphorylation of Akt and GSK3β in the frontal cortex induced by MK-801 was normalized by metformin. In conclusion, our results demonstrate that metformin improved schizophrenia-like symptoms in rats, and is therefore a potential agent for the treatment of schizophrenia.

Effects of adult enriched environment on cognition, hippocampal-prefrontal plasticity and NMDAR subunit expression in MK-801-induced schizophrenia model

Schizophrenia is a mental disorder characterized by psychosis, negative symptoms and cognitive impairment. Cognitive deficits are enduring and represent the most disabling symptom but are currently poorly treated. N-methyl D-aspartate receptor (NMDAR) hypofunction hypothesis has been notably successful in explaining the pathophysiological findings and symptomatology of schizophrenia. Thereby, NMDAR blockade in rodents represents a useful tool to identify new therapeutic approaches. In this regard, enriched environment (EE) could play an essential role. Using a multilevel approach of behavior, electrophysiology and protein analysis, we showed that a short-term exposure to EE in adulthood ameliorated spatial learning and object-place associative memory impairment observed in postnatally MK-801-treated Long Evans rats. Moreover, EE in adult life restored long-term potentiation (LTP) in hippocampal-medial prefrontal pathway abolished by MK-801 treatment. EE in adulthood also induced a set of modifications in the expression of proteins related to glutamatergic neurotransmission. Taken together, these findings shed new light on the neurobiological effects of EE to reverse the actions of MK-801 and offer a preclinical testing of a therapeutic strategy that may be remarkably effective for managing cognitive symptoms of schizophrenia.

Long-lasting effects of repeated ketamine administration in adult and adolescent rats

Initiation of ketamine use often occurs in adolescence, yet little is known about long-term consequences when use begins in this developmental period. The current experiments were designed to examine the effects of repeated exposure to ketamine in adolescence on behavior in adulthood. We examined locomotor activity, as well as cognitive function, in animals that received repeated administration of ketamine. Groups of adolescent and adult male rats were treated with ketamine (25 mg/kg) once daily for 10 days. Locomotor activity was assessed following the first injection, following 10 days of injection, and following 20 days of abstinence. Acute locomotor effects and locomotor sensitization were compared in adolescents and adults; cross-sensitization to dextromethorphan, another dissociative with abusive potential, was also examined. In a separate group of animals cognitive deficits were assessed following the 20 day abstinence period in spatial learning and novel object recognition tasks. The locomotor stimulant effect of ketamine was much greater in adolescents than adults. Animals that were repeatedly administered ketamine demonstrated locomotor sensitization immediately after the final injection. However, sensitization only persisted after the abstinence period in animals treated as adults. No cross-sensitization to dextromethorphan was evident. Ketamine failed to produce statistically significant cognitive deficits in either age group, although drug-treated adults showed a trend towards deficits in spatial learning. Repeated use of ketamine produces long-lasting neuroadaptations that may contribute to addiction. Mild lasting memory deficits may occur in adults, although further work is necessary to confirm these findings. The results extend the understanding of potential long-term consequences of ketamine use in adolescents and adults.

Vinpocetine halts ketamine-induced schizophrenia-like deficits in rats: impact on BDNF and GSK-3β/β-catenin pathway

There are increasing evidences supporting the involvement of oxidative stress and neuroinflammation in schizophrenia. Vinpocetine, a nootropic phosphodiesterase-1 inhibitor, was proven to possess anti-oxidant and anti-inflammatory potentials. This research aimed to reveal the likely protective features of vinpocetine against ketamine-induced schizophrenia-like deficits in rats. Additionally, the probable mechanisms contributing to this neuroprotection were also elucidated. Vinpocetine was given (20 mg/kg, i.p.) once a day for 14 days commencing 7 days before administrating ketamine (25 mg/kg i.p.). Risperidone was applied as a reference antipsychotic. Vinpocetine pre-treatment revealed a marked amendment in the hyperlocomotion, anxiety, and short-term memory deficits induced by ketamine in rats. In rats' hippocampus, ketamine induced a drastic increase in tissue levels of dopamine, lipid peroxidation, and pro-inflammatory cytokines along with a significant decrease in glutamate, GABA, SOD, and total anti-oxidant capacity. Also, ketamine induced a reduced level of BDNF together with the potentiation of GSK-3β/β-catenin pathway that led to the destruction of β-catenin. Pre-treatment of ketamine-challenged animals with vinpocetine significantly attenuated oxidative stress, inflammation, and neurotransmitter alterations. Vinpocetine also elevated BDNF expression and prevented ketamine-induced stimulation of the GSK-3β/β-catenin signaling. This research presents enlightenments into the role of vinpocetine in schizophrenia. This role may be accomplished through its effect on oxidative stress, inflammation as well as modulating BDNF and the GSK-3β/β-catenin pathway.