Prefrontal cortex lesions cause only minor effects on the hyperlocomotion induced by MK-801 and its reversal by clozapine

Particulate matter (PM10) exacerbates on MK-801-induced schizophrenia-like behaviors through the inhibition of ERK-CREB-BDNF signaling pathway

Particulate matter (PM), released into the air by a variety of natural and human activities, is a key indicator of air pollution. Although PM is known as the extensive health hazard to affect a variety of illness, few studies have specifically investigated the effects of PM10 exposure on schizophrenic development. In the present study, we aimed to investigate the impact of PM10 on MK-801, N-methyl-D-aspartate (NMDA) receptor antagonist, induced schizophrenia-like behaviors in C57BL/6 mouse. Preadolescent mice were exposed PM10 to 3.2 mg/m3 concentration for 4 h/day for 2 weeks through a compartmentalized whole-body inhalation chamber. After PM10 exposure, we conducted behavioral tests during adolescence and adulthood to investigate longitudinal development of schizophrenia. We found that PM10 exacerbated schizophrenia-like behavior, such as psychomotor agitation, social interaction deficits and cognitive deficits at adulthood in MK-801-induced schizophrenia animal model. Furthermore, the reduced expression levels of brain-derived neurotrophic factor (BDNF) and the phosphorylation of BDNF related signaling molecules, extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB), were exacerbated by PM10 exposure in the adult hippocampus of MK-801-treated mice. Thus, our present study demonstrates that exposure to PM10 in preadolescence exacerbates the cognitive impairment in animal model of schizophrenia, which are considered to be facilitated by the decreased level of BDNF through reduced ERK-CREB expression.

Paeonol, the active component of Cynanchum paniculatum, ameliorated schizophrenia-like behaviors by regulating the PI3K-Akt-GSK3β-NF-κB signalling pathway in MK-801-treated mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cynanchum paniculatum (Bunge) Kitag. ex H. Hara (Asclepiadaceae) have been traditionally used in East Asia as analgesic or antiviral agents. Interestingly, some Chinese and Korean traditional medicinal books reported that the use of C. paniculatum in the treatment of psychotic symptoms, such as hallucinations and delusions.

AIM OF THE STUDY

In this study, we aimed to investigate whether C. paniculatum could improve sensorimotor gating disruption in mice with MK-801-induced schizophrenia-like behaviors. We also aimed to identify the active component of C. paniculatum that could potentially serve as a treatment for schizophrenia and found that paeonol, the major constituent compound of C. paniculatum, showed potential as a treatment for schizophrenia.

MATERIALS AND METHODS

To assess the effect of paeonol on mice with MK-801-induced schizophrenia-like behaviors, we carried out a series of behavioral tests related with symptoms of schizophrenia. In addition, we utilized Western blotting and ELISA techniques to investigate the antipsychotic actions of paeonol.

RESULT

C. paniculatum extract (100 or 300 mg/kg) and paenol (10 or 30 mg/kg) significantly reversed MK-801-induced prepulse deficits in acoustic startle response test. In addition, paeonol (10 or 30 mg/kg) attenuated social novelty preference and novel object recognition memory on MK-801-induced schizophrenia-like behaviour in mice. Furthermore, the phosphorylation levels of PI3K, Akt, GSK3β and NF-κB, as well as related pro-inflammatory cytokine, such as IL-1β and TNF-α, were significantly reversed by the administration of paeonol (10 or 30 mg/kg) in the prefrontal cortex of MK-801-treated mice.

CONCLUSIONS

Collectively, these data show that paeonol can potentially be used as an agent for treating sensorimotor gating deficits, negative symptoms, and cognitive deficits, such as those observed in schizophrenia with few adverse effects.

Discrimination of motor and sensorimotor effects of phencyclidine and MK-801: Involvement of GluN2C-containing NMDA receptors in psychosis-like models

Non-competitive NMDA receptor (NMDA-R) antagonists like ketamine, phencyclidine (PCP) and MK-801 are routinely used as pharmacological models of schizophrenia. However, the NMDA-R subtypes, neuronal types (e.g., GABA vs. glutamatergic neurons) and brain regions involved in psychotomimetic actions are not fully understood. PCP activates thalamo-cortical circuits after NMDA-R blockade in reticular thalamic GABAergic neurons. GluN2C subunits are densely expressed in thalamus and cerebellum. Therefore, we examined their involvement in the behavioral and functional effects elicited by PCP and MK-801 using GluN2C knockout (GluN2CKO) and wild-type mice, under the working hypothesis that psychotomimetic effects should be attenuated in mutant mice. PCP and MK-801 induced a disorganized and meandered hyperlocomotion in both genotypes. Interestingly, stereotyped behaviors like circling/rotation, rearings and ataxia signs were dramatically reduced in GluN2CKO mice, indicating a better motor coordination in absence of GluN2C subunits. In contrast, other motor or sensorimotor (pre-pulse inhibition of the startle response) aspects of the behavioral syndrome remained unaltered by GluN2C deletion. PCP and MK-801 evoked a general pattern of c-fos activation in mouse brain (including thalamo-cortical networks) but not in the cerebellum, where they markedly reduced c-fos expression, with significant genotype differences paralleling those in motor coordination. Finally, resting-state fMRI showed an enhanced cortico-thalamic-cerebellar connectivity in GluN2CKO mice, less affected by MK-801 than controls. Hence, the GluN2C subunit allows the dissection of the behavioral alterations induced by PCP and MK-801, showing that some motor effects (in particular, motor incoordination), but not deficits in sensorimotor gating, likely depend on GluN2C-containing NMDA-R blockade in cerebellar circuits.

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-3β 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.

Spirulina platensis reduces the schizophrenic-like symptoms in rat model by restoring altered APO-E and RTN-4 protein expression in prefrontal cortex

AIMS

Schizophrenia (SZ) is recognized as a neuropsychiatric disorder in humans with accelerated mortality and profound morbidity followed with impairments in social as well as vocational functioning. Though various antipsychotics are being considered as approved treatment therapy for the psychotic symptoms of SZ but they also exert adverse effects and also lack efficacy in treating full spectrum of the disorder. Spirulina platensis (blue-green algae), a nutritional supplement, constitutes a variety of multi-nutrients and possesses a large number of neuroprotective activities. Therefore, present experimental work was designed to evaluate the neuroprotective effects of spirulina in ameliorating the psychosis-like symptoms in dizocilpine-induced rat model of SZ.

MATERIALS AND METHODS

The spirulina was tested as preventive and therapeutic regimen at the dose of 180 mg/kg. After pre- and post-treatment with spirulina, rats were subjected to behavioral assessments followed by biochemical and neurochemical estimations. Biomarkers including APO-E, RTN-4, TNF-α, and IL-6 were also estimated using ELISA.

KEY FINDINGS

Present results showed that administration of spirulina not only improved behavioral deficits induced by dizocilpine but it also regulates neurotransmission, oligodendrocyte dysfunction and APO-E over expression. Moreover, it also restores the immune response dysfunction by reducing inflammatory cytokines.

SIGNIFICANCE

Thus, from present findings it may be suggested that spirulina aids in ameliorating the psychosis-like symptoms induced by dizocilpine in animal model possibly via regulation of neurotransmission and other biomarkers that are extensively used to uncover the etiopathology of SZ. Hence, blue-green algae can be used as an effective therapy for preventive or therapeutic measures in SZ.

Neuro-behavioral effects after systemic administration of MK-801 and disinhibition of the anterior thalamic nucleus in rats: Potential relevance in schizophrenia

Non-competitive N-methyl-d-aspartate receptor (NMDA-R) antagonists have been suggested to evoke psychotomimetic-like behaviors by selectively targeting GABAergic elements in cortical and thalamic circuits. In previous studies, we had reported the involvement of the reticular and anterior thalamic nuclei (ATN) in the MK-801-evoked hyperactivity and other motor alterations. Consistent with the possibility that these responses were mediated by thalamic disinhibition, we examined the participation of cortical and hippocampal areas innervated by ATN in the responses elicited by the systemic administration of MK-801 (0.2 mg/kg) and compared them to the effects produced by the microinjection of a subconvulsive dose of bicuculline (GABA_A receptor antagonist) in the ATN. We used the expression of Fos related antigen 2 (Fra-2) as a neuronal activity marker in the ATN and its projection areas such as hippocampus (HPC), retrosplenial cortex (RS), entorhinal cortex (EC) and medial prefrontal cortex (mPFC). Dorsal (caudate-putamen, CPu) and ventral striatum (nucleus accumbens, core and shell, NAc,co and NAc,sh) were also studied. Behavioral and brain activation results suggest a partial overlap after the effect of MK-801 administration and ATN disinhibition. MK-801 and ATN disinhibition increases locomotor activity and disorganized movements, while ATN disinhibition also reduces rearing behavior. A significant increase in Fra-2 immunoreactivity (Fra-2-IR) in the ATN, mPFC (prelimbic area, PrL) and NAc,sh was observed after MK-801, while a different pattern of Fra-2-IR was detected following ATN disinhibition (e.g., increase in DG and NAc,sh, and decrease in PrL cortex). Overall, our data may contribute to the understanding of dysfunctional neural circuits involved in schizophrenia.

Vortioxetine Differentially Modulates MK-801-Induced Changes in Visual Signal Detection Task Performance and Locomotor Activity

Attention impairment is a common feature of Major Depressive Disorder (MDD), and MDD-associated cognitive dysfunction may play an important role in determining functional status among this patient population. Vortioxetine is a multimodal antidepressant that may improve some aspects of cognitive function in MDD patients, and may indirectly increase glutamate neurotransmission in brain regions classically associated with attention function. Previous non-clinical research suggests that vortioxetine has limited effects on attention. This laboratory previously found that vortioxetine did not improve attention function in animals impaired by acute scopolamine administration, using the visual signal detection task (VSDT). However, vortioxetine has limited effects on acetylcholinergic neurotransmission, and thus it is possible that attention impaired by other mechanisms would be attenuated by vortioxetine. This study sought to investigate whether acute vortioxetine administration can attenuate VSDT impairments and hyperlocomotion induced by the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801. We found that acute vortioxetine administration had no effect on VSDT performance on its own, but potentiated MK-801-induced VSDT impairments. Furthermore, vortioxetine had no effect on locomotor activity on its own, and did not alter MK-801-induced hyperlocomotion. We further investigated whether vortioxetine's effect on MK-801 could be driven by a kinetic interaction, but found that plasma and brain exposure for vortioxetine and MK-801 were similar whether administered alone or in combination. Thus, it appears that vortioxetine selectively potentiates MK-801-induced impairments in attention without altering its effects on locomotion, and further that this interaction must be pharmacodynamic in nature. A theoretical mechanism for this interaction is discussed.

EEG 40 Hz Coherence Decreases in REM Sleep and Ketamine Model of Psychosis

Cognitive processes are carried out during wakefulness by means of extensive interactions between cortical and subcortical areas. In psychiatric conditions, such as psychosis, these processes are altered. Interestingly, REM sleep where most dreams occurs, shares electrophysiological, pharmacological, and neurochemical features with psychosis. Because of this fact, REM sleep is considered a natural model of psychosis. Ketamine is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist that at sub-anesthetic dose induces psychotomimetic-like effects in humans and animals, and is employed as a pharmacological model of psychosis. Oscillations in the gamma frequency band of the electroencephalogram (EEG), mainly at about 40 Hz, have been involved in cognitive functions. Hence, the present study was conducted to analyze the EEG low gamma (30-45 Hz) band power and coherence of the cat, in natural (REM sleep) and pharmacological (sub-anesthetic doses of ketamine) models of psychosis. These results were compared with the gamma activity during alert (AW) and quiet wakefulness (QW), as well as during non-REM (NREM) sleep. Five cats were chronically prepared for polysomnographic recordings, with electrodes in different cortical areas. Basal recordings were obtained and ketamine (5, 10, and 15 mg/kg, i.m.) was administrated. Gamma activity (power and coherence) was analyzed in the abovementioned conditions. Compared to wakefulness and NREM sleep, following ketamine administration gamma coherence decreased among all cortical regions studied; the same coherence profile was observed during REM sleep. On the contrary, gamma power was relatively high under ketamine, and similar to QW and REM sleep. We conclude that functional interactions between cortical areas in the gamma frequency band decrease in both experimental models of psychosis. This uncoupling of gamma frequency activity may be involved in the cognitive features shared by dreaming and psychosis.

Acute N-methyl-D-aspartate receptor hypofunction induced by MK801 evokes sex-specific changes in behaviors observed in open-field testing in adult male and proestrus female rats

Schizophrenia is a complex constellation of positive, negative and cognitive symptoms. Acute administration of the non-competitive antagonist of the N-methyl-d-aspartate receptor (NMDAR) dizocilpine (MK801) in rats is one of few preclinical animal models of this disorder that has both face and/or construct validity for these multiple at-risk behavioral domains and predictive power for the efficacy of therapeutic drugs in treating them. This study asked whether and to what extent the rat NMDAR hypofunction model also embodies the sex differences that distinguish the symptoms of schizophrenia and their treatment. Thus, we compared the effects of acute MK801, with and without pretreatment with haloperidol or clozapine, on seven discrete spontaneous open-field activities in adult male and female rats. These analyses revealed that MK801 was more effective in stimulating ataxia and locomotion and inhibiting stationary behavior in females while more potently stimulating stereotypy and thigmotaxis and inhibiting rearing and grooming in males. Haloperidol and clozapine pretreatments had markedly different efficacies in terms of behaviors but strong similarities in their effectiveness in male and female subjects. These results bear intriguing relationships with the complex male/female differences that characterize the symptoms of schizophrenia and suggest possible applications for acute NMDAR hypofunction as a preclinical model for investigating the neurobiology that underlies them.

Importance of inter-hemispheric prefrontal connection in the effects of non-competitive NMDA receptor antagonists

Previous studies have shown that systemic, but not unilateral intra-prefrontal cortex administration of non-competitive NMDA antagonists, increased prefrontal activity, the cortical efflux of serotonin, and induced stereotypies. In this work we used in-vivo microdialysis and immunohistochemistry to test the hypothesis as to whether MK-801 and ketamine need to act on both prefrontal cortices to reproduce these neurochemical and behavioural changes. Dialysis probes were implanted in the medial prefrontal cortex, and extracellular serotonin as well as behavioural stereotypies was measured after systemic administration of MK-801 and ketamine (1 mg/kg and 25 mg/kg, respectively), and unilateral and bilateral perfusion of both drugs (300 μm and 3 mm, respectively). Additionally, the prefrontal (glutamatergic) level of activity was measured using c-Fos immunohistochemistry. Systemic and bilateral (but not unilateral) prefrontal administration of MK-801 and ketamine increased serotonin efflux whereas only systemic administration of both drugs produced hyperlocomotion and stereotypies. The unilateral perfusion of 1 μm tetrodotoxin in the medial prefrontal cortex reduced increases of serotonin in both hemispheres, the expression of c-Fos in the contralateral side, and stereotypy scores after systemic NMDA antagonists. Our results support the hypothesis that a bilateral impairment of cortical inhibition in the medial prefrontal cortex is needed for non-competitive NMDA antagonists to induce the state of pyramidal cell hyperactivity and concurrent efflux of serotonin. Furthermore, hyperlocomotion and stereotypies produced by MK-801 and ketamine do not appear to result from changes in the activity of prefrontal cortex although this structure exerts some control over these behaviours.

Role of the anterior thalamic nucleus in the motor hyperactivity induced by systemic MK-801 administration in rats

Non-competitive N-methyl-D-aspartate receptor (NMDA-R) antagonists have been extensively used in rodents to model psychotic symptoms of schizophrenia. Although the motor syndrome induced by acute and systemic administration of low doses of dizocilpine (MK-801) has been extensively characterized, its neurobiological basis is not fully understood. NMDA-R antagonists can disinhibit excitatory inputs in certain brain areas, but the precise circuitry is not fully known. We examined the involvement of the anterior thalamic nucleus (ATN) in hyperlocomotion and other related behaviors (stereotypies, ataxia signs) induced after acute systemic administration of MK-801. Since GABAergic neurons of the reticular thalamic nucleus (RTN) exert the main inhibitory control on thalamic projection neurons, we hypothesized that systemically injected MK-801 might block NMDA-R on RTN GABAergic neurons. This effect would subsequently result in disinhibition of GABAergic inputs onto ATN projections to cortical motor areas, thereby inducing behavioral effects. We evaluated the behavioral syndrome induced by the systemic administration MK-801 (0.2 mg/kg) in control rats and in rats subjected to a bilateral stereotaxic infusion of the GABA(A) agonist muscimol (0.2 μl of 2.5 and 5.0 mM; 0.5-1 nmol per application, respectively) into the ATN. As previously reported, MK-801-induced hyperlocomotion in parallel with disorganized movements (e.g. not guided by normal exploration) slight ataxia signs and stereotypies. All responses were antagonized by pre-infusion of muscimol but not saline into the ATN. According to our results we suggest that the ATN plays a role on hyperlocomotion evoked by MK-801 and could involve a thalamic GABAergic disinhibition mechanism.

Effect of antipsychotics on spontaneous hyperactivity and hypersensitivity to MK-801-induced hyperactivity in rats prenatally exposed to methylazoxymethanol

Exposure to methylazoxymethanol (MAM) at embryonic day 17 (E17) in the rat has been proposed to be a promising model for schizophrenia that mimics behavioural abnormalities and deficits in prefrontal cortex (PFC) networks. In this study, we investigated for the first time the effects of antipsychotics on abnormal behaviours observed in prenatally MAM-exposed rats. We first examined spontaneous and MK-801-induced locomotor activity in an open field in adult E17 MAM- or saline-exposed rats. Then, the effect of single injections of haloperidol, clozapine and risperidone was investigated in MAM- or sham-exposed rats on spontaneous and MK-801 (0.05 mg/kg)-induced hyperactivity. Risperidone more selectively counteracted the spontaneous hyperactivity in MAM than in sham rats, while haloperidol and clozapine induced similar effects on spontaneous locomotion in both groups. The main result of this study is that all the tested antipsychotics were more effective in attenuating the MK-801-induced hyperlocomotion in MAM than in sham rats. These findings further support the validity of E17 MAM exposure as a model for schizophrenia and add to its heuristic value in screening therapies for schizophrenia.

Coca-paste seized samples characterization: chemical analysis, stimulating effect in rats and relevance of caffeine as a major adulterant

Coca-paste (CP) is a drug of abuse that so far has not been extensively characterized. CP is an intermediate product of the cocaine alkaloid extraction process from coca leaves, hence it has a high content of cocaine base mixed with other chemical substances (impurities) and it is probably adulterated when it reaches the consumers. Despite its high prevalence and distribution through South America, little is known about its effects on the central nervous system. In the present study, a chemical analysis of CP samples from different police seizures was performed to determine the cocaine base content and the presence and content of impurities and adulterants. Some CP representative samples were selected to study the effects on the locomotor activity induced after acute systemic administration in rats as a measure of its stimulant action. The behavioral response was compared to equivalent doses of cocaine. As expected, cocaine was the main component in most of the CP samples assayed. Caffeine was the only active adulterant detected. Interestingly, several CP samples elicited a higher stimulant effect compared to that observed after cocaine when administered at equivalent doses of cocaine base. Combined treatment of cocaine and caffeine, as surrogate of different CP samples mimicked their stimulant effect. We demonstrated that cocaine and caffeine are the main components responsible for the CP-induced stimulant action while the contribution of the impurities was imperceptible.

Blockade of NMDA receptors in the prefrontal cortex increases dopamine and acetylcholine release in the nucleus accumbens and motor activity

OBJECTIVES

The present study investigates the effects of injections of a specific N-methyl-D-aspartic acid (NMDA) antagonist 3-[(R)-2-carboxypiperazin-4-yl]-propyl-1-phophonic acid (CPP) into the prefrontal cortex (PFC) on the extracellular concentrations of dopamine and acetylcholine in the nucleus accumbens (NAc) and on motor activity in the freely moving rat.

MATERIALS AND METHODS

Sprague-Dawley male rats were implanted with guide cannulas into the medial PFC and NAc to perform bilateral microinjections and microdialysis experiments. Spontaneous motor activity was monitored in the open field.

RESULTS

Injections of CPP (1 microg/0.5 microL) into the PFC produced a significant increase of the baseline extracellular concentrations of dopamine (up to 130%), dihydroxyphenylacetic acid (DOPAC; up to 120%), homovanillic acid (HVA; up to 130%), and acetylcholine (up to 190%) in the NAc as well as motor hyperactivity. In the NAc, perfusion of the NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate antagonists CPP (50 microM)+6,7-dinitroquinoxaline-2,3-dione (DNQX; 50 microM) through the microdialysis probe blocked acetylcholine release, but not DOPAC and HVA increases produced by CPP injections into the PFC. Also, increases in motor activity produced by prefrontal injections of CPP were significantly reduced by bilateral injections into the NAc of a mixed D1/D2 antagonist, flupenthixol (5 and 25 microg/0.5 microL). Injections into the NAc of the muscarinic antagonist scopolamine (1 and 10 microg/0.5 microL) further increased, and of the nicotinic antagonist mecamylamine (1 and 10 microg/0.5 microL) did not change, the increases in motor activity produced by prefrontal CPP injections.

CONCLUSIONS

These results suggest that the dysfunction of NMDA receptors in the PFC could be a key factor in the neurochemical and motor effects associated with corticolimbic hyperactivity.