Enriched environment prevents cognitive and motor deficits associated with postnatal MK-801 treatment

Correlation between desynchrony of hippocampal neural activity and hyperlocomotion in the model mice of schizophrenia and therapeutic effects of aripiprazole

AIMS

The hippocampus has been reported to be morphologically and neurochemically altered in schizophrenia (SZ). Hyperlocomotion is a characteristic SZ-associated behavioral phenotype, which is associated with dysregulated dopamine system function induced by hippocampal hyperactivity. However, the neural mechanism of hippocampus underlying hyperlocomotion remains largely unclear.

METHODS

Mouse pups were injected with N-methyl-D-aspartate receptor antagonist (MK-801) or vehicle twice daily on postnatal days (PND) 7-11. In the adulthood phase, one cohort of mice underwent electrode implantation in field CA1 of the hippocampus for the recording local field potentials and spike activity. A separate cohort of mice underwent surgery to allow for calcium imaging of the hippocampus while monitoring the locomotion. Lastly, the effects of atypical antipsychotic (aripiprazole, ARI) were evaluated on hippocampal neural activity.

RESULTS

We found that the hippocampal theta oscillations were enhanced in MK-801-treated mice, but the correlation coefficient between the hippocampal spiking activity and theta oscillation was reduced. Consistently, although the rate and amplitude of calcium transients of hippocampal neurons were increased, their synchrony and correlation to locomotion speed were disrupted. ARI ameliorated perturbations produced by the postnatal MK-801 treatment.

CONCLUSIONS

These results suggest that the disruption of neural coordination may underly the neuropathological mechanism for hyperlocomotion of SZ.

Enriched environment as a nonpharmacological neuroprotective strategy

The structure and functions of the central nervous system are influenced by environmental stimuli, which also play an important role in brain diseases. Enriched environment (EE) consists of producing modifications in the environment of standard laboratory animals to induce an improvement in their biological conditions. This paradigm promotes transcriptional and translational effects that result in ameliorated motor, sensory, and cognitive stimulation. EE has been shown to enhance experience-dependent cellular plasticity and cognitive performance in animals housed under these conditions compared with animals housed under standard conditions. In addition, several studies claim that EE induces nerve repair by restoring functional activities through morphological, cellular, and molecular adaptations in the brain that have clinical relevance in neurological and psychiatric disorders. In fact, the effects of EE have been studied in different animal models of psychiatric and neurological diseases, such as Alzheimer's disease, Parkinson's disease, schizophrenia, ischemic brain injury, or traumatic brain injury, delaying the onset and progression of a wide variety of symptoms of these disorders. In this review, we analyze the action of EE focused on diseases of the central nervous system and the translation to humans to develop a bridge to its application.

LncRNA XR_351665 Contributes to Chronic Pain-Induced Depression by Upregulating DNMT1 via Sponging miR-152-3p

Chronic pain is frequently comorbid with depression. However, the mechanisms underlying chronic pain-induced depression remain unclear. Here, we found that DNA methyltransferase 1 (DNMT1) was upregulated in the central amygdala (CeA) of spared nerve injury (SNI)-induced chronic pain-depression rats, and knockdown of DNMT1 could improve the depression-like behaviors in SNI rats. Additionally, a panel of differentially expressed lncRNAs, including 38 upregulated and 12 downregulated lncRNAs, were identified by microarray analysis. Bioinformatics analysis suggested that the upregulated lncRNA XR_351665 was the upstream molecule to regulate DNMT1 expression. The knockdown of XR_351665 significantly alleviated the depression-like behaviors in SNI rats, whereas overexpression of XR_351665 induced the depression-like behaviors in naïve rats. Further mechanism-related researches uncovered that XR_351665 functioned as a competing endogenous RNA (ceRNA) to upregulate DNMT1 by competitively sponging miR-152-3p, and subsequently promoted the development of chronic pain-induced depression. Our findings suggest that lncRNA XR_351665 is involved in the development of chronic pain-induced depression by upregulating DNMT1 via sponging miR-152-3p. These data provide novel insight into understanding the pathogenesis of chronic pain-induced depression and identify a potential therapeutic target. PERSPECTIVE: LncRNA XR_351665 in CeA functions as a ceRNA to block the inhibitory effect of miR-152-3p on DNMT1 and contributes to the development of chronic pain-induced depression. These data suggest that manipulation of XR_351665/miR-152-3p/DNMT1 axis may be a potential method to attenuate chronic pain-induced depression.

Cortical and thalamic modulation of auditory gating in the posterior parietal cortex of awake mice

Auditory gating (AG) is an adaptive mechanism for filtering out redundant acoustic stimuli to protect the brain against information overload. AG deficits have been found in many mental illnesses, including schizophrenia (SZ). However, the neural correlates of AG remain poorly understood. Here, we found that the posterior parietal cortex (PPC) shows an intermediate level of AG in auditory thalamocortical circuits, with a laminar profile in which the strongest AG is in the granular layer. Furthermore, AG of the PPC was decreased and increased by optogenetic inactivation of the medial dorsal thalamic nucleus (MD) and auditory cortex (AC), respectively. Optogenetically activating the axons from the MD and AC drove neural activities in the PPC without an obvious AG. These results indicated that AG in the PPC is determined by the integrated signal streams from the MD and AC in a bottom-up manner. We also found that a mouse model of SZ (postnatal administration of noncompetitive N-methyl-d-aspartate receptor antagonist) presented an AG deficit in the PPC, which may be inherited from the dysfunction of MD. Together, our findings reveal a neural circuit underlying the generation of AG in the PPC and its involvement in the AG deficit of SZ.

Evaluation of Ayres Sensory Integration® Intervention on Sensory Processing and Motor Function in a Child with Rubinstein-Taybi Syndrome: A Case Report

The Rubinstein-Taybi Syndrome (RSTS) literature is limited about sensory integration, which is a foundational neurological function of the central nervous system that may affect the development of cognitive, social, and motor skills. The aim of this case report was to investigate the effects of Ayres Sensory Integration^® (ASI) intervention on processing and integrating sensations, motor functions and parental goals of 3-year-old child with RSTS. Analysis of assessment data reviewed before and after treatment. Assessment collected by interview, Sensory Profile (SP), Sensory Processing Measure-Preschool (SPM-P) Home, Peabody Developmental Motor Scales-2 (PDMS-2), Gross Motor Function Measurement-88 (GMFM-88), and Gross Motor Function Classification System (GMFCS). Progress toward goals and objectives was measured with Goal Attainment Scale (GAS). ASI intervention was implemented 3 times per week for 8 weeks. At pre-intervention, SP and SPM-P Home revealed prominent sensory processing and integration difficulties in this case. PDMS-2 scores indicated the child was far behind his peers in fine and gross motor areas. In addition, systematic observations determined that the child's GMFCS level was III. After 8 weeks of ASI intervention significant improvements were found in parent reports of sensory processing in the areas of vestibular, tactile, and oral functioning on the Sensory Profile. Gains in functional motor skills were found on the GMFM-88 and the GMFCS. Consistent with these results, significant gains at or above expected levels of performance were found on GAS goals which reflected the family's main concerns for social participation, feeding, play, and movement. There are limited studies on sensory processing and integration in children with RSTS. This case report identified sensory processing and integration difficulties for the first time in a child with RSTS. Results also provide preliminary support for the positive effects of ASI intervention on sensory processing, functional motor skills, and parental goals of a child with RSTS.

Beneficial effects of enriched environment on behavior, cognitive functions, and hippocampal brain-derived neurotrophic factor level following postnatal serotonin depletion in male rats

The neurotransmitter serotonin (5-HT) is one of the most important modulators of neural circuitry and has a critical role in neural development and functions. Previous studies indicated that changes in serotonergic system signaling in early life critically impact mental health, behavior, the morphology of hippocampal neurons, and cognitive functions across the lifespan. The enriched environment (EE) has indicated beneficial effects on behavior and cognitive functions in the developmental period of life, but its impacts on cognitive impairments and behavioral changes following postnatal serotonin depletion are unknown. Therefore, the present study aimed to evaluate the influences of the EE housing (postnatal days [PNDs] 21-60) following postnatal serotonin depletion (by para-chlorophenylalanine [PCPA], 100 mg/kg, s.c, in PNDs 10-20) on anxiety-related behaviors, cognitive functions, and brain-derived neurotrophic factor (BDNF) mRNA expression in the hippocampus of male rats. Memory and behavioral parameters were examined in early adulthood and after that, the hippocampi of rats were removed to determine the BDNF mRNA expression by PCR (PNDs 60-70). The findings of the present work indicated that adolescent EE exposure alleviated memory impairment, decreased BDNF levels, and anxiety disorders induced by experimental depletion of serotonin. Overall, these results indicate that serotonergic system dysregulation during the developmental periods can be alleviated by adolescent EE exposure.

The effects and mechanism of environmental enrichment on MK-801 induced cognitive impairment in rodents with schizophrenia

Schizophrenia is a severe mental disorder characterized by positive, negative, and cognitive symptoms. Cognitive symptoms are a kind of symptoms with high incidence and great impact on patients. There is no effective treatment in clinical practice. N-methyl-d-aspartic acid (NMDA) receptor hypofunction may be an important cause of cognitive symptoms. MK-801 (also named Dizocilpine), a noncompetitive antagonist of NMDA receptor, is often used to construct a model of NMDA receptor dysfunction. In terms of treatment, environmental enrichment (EE) as an environmental intervention can effectively improve the symptoms of cognitive impairment in rodents. In this paper, we first briefly introduce the background of cognitive symptoms and EE in schizophrenia, and then investigate the manifestations of MK-801 induced cognitive impairment, the improvement of EE on these cognitive impairments based on the MK-801 induced schizophrenia rodent models, and the possible mechanism of EE in improving cognitive symptoms. This article reviews the literature in recent years, which provides an important reference for MK-801 to construct a cognitive symptom model of schizophrenia and the mechanism of EE in improving cognitive symptoms of schizophrenia.

Effect of prenatal different auditory environment on learning ability and fearfulness in chicks

Objective

Early environmental enrichment in life can improve cognition in animals. The effect of prenatal auditory stimulation on learning ability and fear level in chick embryos remained unexplored. Therefore, this study investigated the effect of prenatal auditory stimulation on the learning ability and fear level of chicks.

Methods

A total of 450 fertilized eggs were randomly divided into 5 groups, including control group (C), low-sound intensity music group (LM), low-sound intensity noise group (LN), high-sound intensity noise group (HN) and high-sound intensity music group (HM). From the 10th day of embryonic development until hatching, group LM and group LN received 65 to 75 dB of music and noise stimulation. Group HN and group HM received 85 to 95 dB of noise and music stimulation, and group C received no additional sound. At the end of incubation, the one-trial passive avoidance learning (PAL) task and tonic immobility (TI) tests were carried out, and the serum corticosterone (CORT) and serotonin (5-HT) concentrations were determined.

Results

The results showed that compared with the group C, 65 to 75 dB of music and noise stimulation did not affect the PAL avoidance rate (p>0.05), duration of TI (p>0.05) and the concentration of CORT (p>0.05) and 5-HT (p>0.05) in chicks. However, 85 to 95 dB of music and noise stimulation could reduce duration of TI (p<0.05) and the concentration of CORT (p<0.05), but no significant effect was observed on the concentration of 5-HT (p>0.05) and PAL avoidance rate (p>0.05).

Conclusion

Therefore, the prenatal auditory stimulation of 85 to 95 dB can effectively reduce the fear level of chicks while it does not affect the learning ability.

Adolescent enriched environment exposure alleviates cognitive impairment in sleep-deprived male rats: Role of hippocampal BDNF

Developmental life experience has long-lasting influences on the brain and behavior. The present study aims to examine the long-term effects of the enriched environment (EE), which was imposed during the adolescence period of life, on their passive avoidance and recognition memories as well as anxiety-like behaviors and hippocampal brain-derived neurotrophic factor (BDNF) levels, in sleep-deprived male rats. In the present study, the male pups were separated from their mothers in postnatal day 21 (PND21) and were housed in the standard or EE for 40 days. In PND 61, the rats were allocated in four groups: control, SD (sleep deprivation), EE, and EE+SD groups. Sleep deprivation was induced in rats by a modified multiple platform model for 24 hours. Open field, novel object recognition memory, and passive avoidance memory tests were used to examine behavior and cognitive ability. The expression of hippocampal BDNF levels was determined by PCR. The results revealed that SD increased anxiety-like behaviors and impaired cognitive ability, while adolescent EE housing alleviated these changes. In addition, EE reversed SD-induced changes in hippocampal BDNF level. We also demonstrated that EE not only has beneficial effects on the cognitive functions of normal rats but also declined memory deficits induced by sleep deprivation. In conclusion, our results suggest that housing in EE during the adolescence period of life reduces cognitive impairment induced by SD. The increase of the BDNF level in the hippocampus is a possible mechanism to alleviate cognitive performance in sleep-deprived rats.

Activation of D1/D5 Receptors Ameliorates Decreased Intrinsic Excitability of Hippocampal Neurons Induced by Neonatal Blockade of NMDA Receptors

BACKGROUND AND PURPOSE

Dysregulation of dopaminergic transmission combined with transient hypofunction of N-methyl-D-aspartate receptors (NMDARs) is a key mechanism that may underlie cognitive symptoms of schizophrenia.

EXPERIMENTAL APPROACH

Therefore, we aimed to identify electrophysiologic alterations in animals neonatally treated with the NMDA receptor antagonist, MK-801 or with saline solution.

KEY RESULTS

Patch-clamp whole-cell recordings from MK-801-treated animals revealed altered passive and active electrophysiologic properties compared with CA1 pyramidal cells from saline-treated animals, including upregulation of the K⁺ inward-rectifier conductance and fast-inactivating and slow/non-inactivating K⁺ currents. Upregulation of these membrane ionic currents reduced the overall excitability and altered the firing properties of CA1 pyramidal cells. We also explored the capability of cells treated with MK-801 to express intrinsic excitability potentiation, a non-synaptic form of hippocampal plasticity associated with cognition and memory formation. CA1 pyramidal cells from animals treated with MK-801 were unable to convey intrinsic excitability potentiation and had blunted synaptic potentiation. Furthermore, MK-801-treated animals also exhibited reduced cognitive performance in the Barnes maze task. Notably, activation of D1/D5 receptors with SKF-38, 393 partially restored electrophysiologic alterations caused by neonatal treatment with MK-801.

CONCLUSION AND IMPLICATIONS

Our results offer a molecular and mechanistic explanation based on dysregulation of glutamatergic in addition to dopaminergic transmission that may contribute to the understanding of the cognitive deterioration associated with schizophrenia.

Antipsychotic-like profile of CIQ isomers in animal models of schizophrenia

Earlier, we have shown the efficacy of racemic (±) CIQ, a positive allosteric modulator of GluN2C/2D receptor against MK-801 induced impairment of prepulse inhibition as well as working memory. The present study investigated the antipsychotic-like profile of different CIQ (±, +, -) isomers against schizophrenia-like symptoms in series of behavioural animal models like apomorphine climbing, social isolation behaviour and NMDA receptor antagonist MK-801 induced cognitive deficits. Further, we also tested CIQ (±, +, -) isomers in neurodevelopmental model against MK-801induced deficits using open field test, Y-maze test and novel object recognition test. CIQ (±, +, -) isomers decreased climbing behaviour, increased social interaction and improved the MK-801 induced deficits in working memory in Y-maze. Further, CIQ (±, +) but not CIQ (-) improved the recognition memory in novel object recognition test as well as reduced hyperlocomotion and stereotyped behaviour. We conclude that CIQ (±, +) but not CIQ (-) exhibit the significant antipsychotic-like profile.

Environmental enrichment or selective activation of parvalbumin-expressing interneurons ameliorates synaptic and behavioral deficits in animal models with schizophrenia-like behaviors during adolescence

Synaptic deficit-induced excitation and inhibition (E/I) imbalance have been implicated in the pathogenesis of schizophrenia. Using in vivo two-photon microscopy, we examined the dynamic plasticity of dendritic spines of pyramidal neurons (PNs) and "en passant" axonal bouton of parvalbumin-expressing interneurons (PVINs) in the frontal association (FrA) cortex in two adolescent mouse models with schizophrenia-like behaviors. Simultaneous imaging of PN dendritic spines and PV axonal boutons showed that repeated exposure to N-methyl-D-aspartate receptor (NMDAR) antagonist MK801 during adolescence disrupted the normal developmental balance of excitatory and inhibitory synaptic structures. This MK801-induced structural E/I imbalance significantly correlated with animal recognition memory deficits and could be ameliorated by environmental enrichment (EE). In addition, selective chemogenetic activation of PVINs in the FrA mimicked the effects of EE on both synaptic plasticity and animal behavior, while selective inhibition of PVIN abolished EE's beneficial effects. Electrophysiological recordings showed that chronic MK801 treatment significantly suppressed the frequency of mEPSC/mIPSC ratio of layer (L) 2/3 PNs and significantly reduced the resting membrane potential of PVINs, the latter was rescued by selective activation of PVINs. Such manipulations of PVINs also showed similar effects in PV-Cre; ErbB4^fl/fl animal model with schizophrenia-like behaviors. EE or selective activation of PVINs in the FrA restored behavioral deficits and structural E/I imbalance in adolescent PV-Cre; ErbB4^fl/fl mice, while selective inhibition of PVINs abolished EE's beneficial effects. Our findings suggest that the PVIN activity in the FrA plays a crucial role in regulating excitatory and inhibitory synaptic structural dynamics and animal behaviors, which may provide a potential therapeutic target for schizophrenia treatment.

Enriched Environment Rearing from Birth Reduced Anxiety, Improved Learning and Memory, and Promoted Social Interactions in Adult Male Mice

Rearing rodents in an enriched environment (EE), with increased sensory stimulations and social interactions, is a well-established model for naturally increasing neural activity. It is well-known that EE-rearing of rodents from adolescence or during adulthood leads to extensive biochemical, morphological, electrophysiological and behavioral changes. Here, we examine the effects of EE-rearing from birth on adult behavior. Through a battery of assays, we found that mice EE-reared from birth had better acquisition and consolidation of memory, in both aversive-based fear conditioning and reward-based contextual association tasks. Moreover, EE-reared mice showed reduced anxiety in novel environments and enhanced social interactions. Together, these results demonstrated that EE-rearing from birth significantly improved motor ability, learning and memory and sociability, while reducing anxiety. A better understanding of how early environmental influences affect behavior is not only important for understanding neural circuit wiring, but also provides insight into developing more effective intervention programs for neurodevelopmental disorders.

Effects of psychological or physical prenatal stress on attention and locomotion in juvenile rats

Background: Prenatal stress has been shown to affect the cognition of offspring, including memory and learning abilities.Methods: In the current study, the long-term effects of chronic prenatal exposure to the physical or psychological stress on locomotion and attention were evaluated by using open field test (OFT) and prepulse inhibition (PPI) of the acoustic startle reflex (ASR). In addition, the level of corticosterone was measured after the ASR trial.Results: Male and female rodents that underwent prenatal physical and psychological stress had an augmented velocity in OFT, and only male animals showed an increased ASR. Neither male nor female offsprings had an alteration in the level of corticosterone and PPI values regardless of the stress type.Conclusion: Our results revealed that exposure to stress during the development of fetus increases ASR in a sex-dependent manner. This finding might implicate the effect of prenatal stress on attention in male offspring regardless of the stress type.

Memory deterioration based on the tobacco smoke exposure and methylazoxymethanol acetate administration vs. aripiprazole, olanzapine and enrichment environment conditions

Enrichment environment conditions, as well as tobacco smoke exposure, may affect cognitive function (e.g. spatial memory) in an animal model of schizophrenia and schizophrenic patients. The aim of this study was to find whether spatial memory function impairment is found in methylazoxymethanol acetate treated rats (an animal model of schizophrenia) and whether aripiprazole (1.5 mg/kg) and olanzapine (0.5 mg/kg) modify these functions. We also were able to determine whether tobacco smoke exposure and enrichment environment conditions have an impact on drug efficacy. The effect of methylazoxymethanol acetate, tobacco smoke exposure, enrichment environment and the use of drugs were studied in the Morris Water Maze test (spatial memory). The results of our study clearly show that enriched environment may have a procognitive effect while tobacco smoke and methylazoxymethanol acetate have a contradictory effect. This paper also confirmed that the use of neuroleptics, namely ARI and OLA, reduced the process of spatial memory deterioration tested in the Morris water maze both in terms of the number of escape latencies and crossed quadrants.

Enriched Environment Reverts Somatostatin Interneuron Loss in MK-801 Model of Schizophrenia

Dysregulation of the inhibitory drive has been proposed to be a central mechanism to explain symptoms and pathophysiological hallmarks in schizophrenia. A number of recent neuroanatomical studies suggest that certain types of inhibitory cells are deficient in schizophrenia, including somatostatin-immunoreactive interneurons (SST+). The present study sought to use stereological methods to investigate whether the number of SST+ interneurons decreased after repeated injections of NMDA receptor antagonist MK-801 (0.5 mg/kg) and to determine the effect of limited exposure to an enriched environment (EE) in adult life on this sub-population of inhibitory cells. Considering that somatostatin expression is highly dependent on neurotrophic support, we explored the changes in the relative expression of proteins related to brain-derived neurotrophic factor-tyrosine kinase B (BDNF-TrkB) signaling between the experimental groups. We observed that early-life MK-801 treatment significantly decreased the number of SST+ interneurons in the medial prefrontal cortex (mPFC) and the hippocampus (HPC) of adult Long Evans rats. Contrarily, short-term exposure to EE increased the number of SST+ interneurons in MK-801-injected animals, except in the CA1 region of the hippocampus, whereas this increase was not observed in vehicle-injected rats. We also found upregulated BDNF-TrkB signaling after EE that triggered an increase in the pERK/ERK ratio in mPFC and HPC, and the pAkt/Akt ratio in HPC. Thus, the present results support the notion that SST+ interneurons are markedly affected after early-life NMDAR blockade and that EE promotes SST+ interneuron expression, which is partly mediated through the BDNF-TrkB signaling pathway. These results may have important implications for schizophrenia, as SST+ interneuron loss is also observed in the MK-801 pre-clinical model, and its expression can be rescued by non-pharmacological approaches.

Short-Term Exposure to Enriched Environment in Adult Rats Restores MK-801-Induced Cognitive Deficits and GABAergic Interneuron Immunoreactivity Loss

Perinatal injections of N-methyl-D-aspartate (NMDA) receptor antagonist in rodents emulate some cognitive impairments and neurochemical alterations, such as decreased GABAergic (gamma aminobutyric acid) interneuron immunoreactivity, also found in schizophrenia. These features are pervasive, and developing neuroprotective or neurorestorative strategies is of special interest. In this work, we aimed to investigate if a short exposure to enriched environment (EE) in early adulthood (P55-P73) was an effective strategy to improve cognitive dysfunction and to restore interneuron expression in medial prefrontal cortex (mPFC) and hippocampus (HPC). For that purpose, we administered MK-801 intraperitoneally to Long Evans rats from postnatal days 10 to 20. Twenty-four hours after the last injection, MK-801 produced a transient decrease in spontaneous motor activity and exploration, but those abnormalities were absent at P24 and P55. The open field test on P73 manifested that EE reduced anxiety-like behavior. In addition, MK-801-treated rats showed cognitive impairment in novel object recognition test that was reversed by EE. We quantified different interneuron populations based on their calcium-binding protein expression (parvalbumin, calretinin, and calbindin), glutamic acid decarboxylase 67, and neuronal nuclei-positive cells by means of unbiased stereology and found that EE enhanced interneuron immunoreactivity up to normal values in MK-801-treated rats. Our results demonstrate that a timely intervention with EE is a powerful tool to reverse long-lasting changes in cognition and neurochemical markers of interneurons in an animal model 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.

NMDA receptor dependence of reversal learning and the flexible use of cognitively demanding search strategies in mice

Cognitive flexibility helps organisms to respond adaptively to environmental changes. Deficits in this executive function have been associated with a variety of brain disorders, and it has been shown to rely on various concomitant neurobiological mechanisms. However, the involvement of the glutamatergic system in general, and NMDA receptors in particular, has been debated. Therefore, we injected C57BL/6 mice repeatedly with low-doses of the non-competitive NMDA receptor antagonist MK-801 (dizocilpine, 0.1 mg/kg, i.p.). Reversal learning and the use of specific cognitive strategies were assessed in a non-spatial discrimination touchscreen task and the Morris water maze (MWM) spatial learning task. In addition, mice were subjected to a non-mnemonic test battery. Although initial acquisition learning was not affected by MK-801 administration, it did induce deficits in reversal learning, both in the non-spatial and spatial task. Defects in non-spatial reversal learning appeared to be caused by perseverative errors. Also, MK-801 administration induced perseverative behaviours as well as inefficient spatial strategy use during MWM reversal learning. These effects could not be reduced to changes in exploratory (anxiety-related) behaviours, nor to motor deficits. This was consistent with results in the non-mnemonic test battery, during which MK-801 evoked hyperlocomotion and subtle motor defects, but failed to alter general motor activity and exploratory behaviours. In conclusion, NMDA receptors appear to be involved in the flexible cognitive processes that underlie reversal learning in spatial as well as non-spatial tasks. Our results also indicate that reversal learning as well as the use of cognitively demanding strategies are more sensitive to NMDA receptor blockage than some other functions that have been suggested to be NMDA receptor dependent.

Effects of Intraperitoneal N-methyl-D-aspartate (NMDA) Administration on Nociceptive/Repetitive Behaviors in Juvenile Mice

Dysregulation of excitatory neurotransmission has been implicated in the pathogenesis of neuropsychiatric disorders. Pharmacological inhibition of N-methyl-D-aspartate (NMDA) receptors is widely used to model neurobehavioral pathologies and underlying mechanisms. There is ample evidence that overstimulation of NMDA-dependent neurotransmission may induce neurobehavioral abnormalities, such as repetitive behaviors and hypersensitization to nociception and cognitive disruption, pharmacological modeling using NMDA has been limited due to the induction of neurotoxicity and blood brain barrier breakdown, especially in young animals. In this study, we examined the effects of intraperitoneal NMDA-administration on nociceptive and repetitive behaviors in ICR mice. Intraperitoneal injection of NMDA induced repetitive grooming and tail biting/licking behaviors in a dose- and age-dependent manner. Nociceptive and repetitive behaviors were more prominent in juvenile mice than adult mice. We did not observe extensive blood brain barrier breakdown or neuronal cell death after peritoneal injection of NMDA, indicating limited neurotoxic effects despite a significant increase in NMDA concentration in the cerebrospinal fluid. These findings suggest that the observed behavioral changes were not mediated by general NMDA toxicity. In the hot plate test, we found that the latency of paw licking and jumping decreased in the NMDA-exposed mice especially in the 75 mg/kg group, suggesting increased nociceptive sensitivity in NMDA-treated animals. Repetitive behaviors and increased pain sensitivity are often comorbid in psychiatric disorders (e.g., autism spectrum disorder). Therefore, the behavioral characteristics of intraperitoneal NMDA-administered mice described herein may be valuable for studying the mechanisms underlying relevant disorders and screening candidate therapeutic molecules.

Enriched Environment Significantly Reduced Senile Plaques in a Transgenic Mice Model of Alzheimer's Disease, Improving Memory

Alzheimer's disease (AD) is associated with a progressive dementia, and there is good evidence that it is more pronounced in individuals that have fewer stimuli during their lives. Environmental stimulation promotes morphological and functional changes in the brain, leading to amplification of cognitive functions, and has been described in humans and animals. In this study, we evaluated the effects of enriched environment (EE) stimulation on spatial memory and senile plaque formation in transgenic mice PDGFB-APPSwInd (TG) that overexpress the human amyloid precursor protein, normally resulting in an increased density of senile plaques. We compared this group of EE stimulated transgenic mice (TG-EE) with an EE stimulated control group of age-matched C57Bl/6 wild type animals (WT-EE). Both groups were exposed to EE stimulation between the ages of 8 and 12 months. As controls of the experiment, there were a group of TG mice not exposed to EE (TG-Ctrl) and a group of WT mice not exposed to EE (WT-Ctrl). The TG-EE group presented improved spatial memory when compared to the TG-Ctrl animals. In addition, the TG-EE group showed a 69.2% reduction in the total density of senile plaques in the hippocampus when compared to the TG-Ctrl group. In this group, the concentration of senile plaques was greater in the dorsal part of the hippocampus, which is linked to spatial localization, and the reduction of this density after the submission to EE was as high as 85.1%. EE stimulation had no effect on the density of amyloid-β (Aβ) oligomers. However, amyloid scavenger receptor class B member 1 (SR-B1) density was significantly decreased in the TG-Ctrl mice, but not in the TG-EE mice, suggesting that cognitive stimulation had an effect on the formation of a cognitive reserve that could prevent the accumulation of senile plaques. It is suggested that the stimulation of old mice by EE for 4 months led to the formation of brain resilience that protected the brain from the deposition of senile plaques, one of the hallmarks of AD, leading to improvement in spatial memory.

Evaluation of prepulse inhibition and memory impairments at early stage of cirrhosis may be considered as a diagnostic index for minimal hepatic encephalopathy

Minimal hepatic encephalopathy (MHE), which represents the early stage of this condition, is not clinically apparent and is prevalent in up to 80% of patients. The poor outcomes of MHE encouraged us to identify more simple methods for early diagnosis of MHE. To this purpose, we evaluated the contemporary manifestations of motor, cognitive and sensorimotor gaiting deficits following bile duct-ligation (BDL). Male Wistar rats were undergone BDL to induce cirrhosis and locomotor, spatial learning and memory and sensorimotor gating were assessed 2, 3, and 4weeks after the operation by rotarod, Morris water-maze and prepulse inhibition (PPI) tests. PPI was examined 6weeks after BDL until appearance of hepatic encephalopathy. Results showed that although PPI was significantly enhanced in the 6-week BDL animals, locomotor activity reduced in 4-week BDL rats compared to the BDL rats after a 2-week period. The total distance travelled and swimming time to reach the platform increased in the 4-week BDL rats and, in contrast, the percentage of time spent and space travelled in correct quadrant decreased. Moreover, memory index decreased in the 3-week BDL group compared to sham-operated group. It was observed an increase in global PPI in 3- and 4-week BDL animals in comparison with either 2-week BDL or sham-operated rats. Consequently, it is indicated that BDL animals manifest spatial learning and memory deficits and PPI disruption in early stage of HE and evaluation of these factors can be considered as indices for simple and early diagnosis of MHE.

Postnatal Administration of Dizocilpine Inhibits Neuronal Excitability in PFC and Induces Social Deficits Detected by MiceProfiler

Schizophrenia is a devastating mental disease with social deficit as its core component of negative symptoms, which could be induced in rodents by dizocilpine (MK-801), a noncompetitive NMDA receptor antagonist. NMDA receptors are highly expressed during the postnatal period. However, less attention has been paid to the effects of postnatal MK-801 administration on social interaction. In this study, we evaluated the effects of postnatal administration of MK-801 on social interaction and explored the possible mechanisms. Postnatal day-7 mice were intraperitoneally injected with MK-801 twice daily for 5 days, and their social interaction repertoire was monitored by a computerized video in the 10th week. The contact event, relative position event, stop-state, and dynamic event were analyzed with MiceProfiler automatic idTracker system. The results showed that MK-801 reduced the number of the contact events, relative position events, and stop-states, while increased the number and duration of dynamic events. These changes implied that MK-801-injected mice had indifference and lower motivation in social interaction and could be a useful model for studies on the social deficit of schizophrenia. The prefrontal cortex is the key region for social interaction behaviors. Slice patch clamp was performed to analyze the cellular excitability of prefrontal cortical neurons after postnatal treatment with MK-801 in mice. The results demonstrated that MK-801 injection reduced the frequency and amplitude of action potentials, but increased the frequency of miniature inhibitory postsynaptic currents. These data illustrated that the excitability of neurons in the prefrontal cortex was inhibited. Finally, immunoblotting data demonstrated that MK-801 significantly decreased the levels of sirtuin 1 (SIRT1) and phosphorylated protein kinase B (p-PKB) in the prefrontal cortex (both P < 0.05). Taken together, our results indicated that administration of MK-801 to postnatal mice induces social interaction deficits possibly due to inhibiting the neuronal excitability and decreasing the levels of SIRT1 and p-PKB in the prefrontal cortex.

Prenatal immune activation in mice blocks the effects of environmental enrichment on exploratory behavior and microglia density

Adverse environmental factors including prenatal maternal infection are capable of inducing long-lasting behavioral and neural alterations which can enhance the risk to develop schizophrenia. It is so far not clear whether supportive postnatal environments are able to modify such prenatally-induced alterations. In rodent models, environmental enrichment influences behavior and cognition, for instance by affecting endocrinologic, immunologic, and neuroplastic parameters. The current study was designed to elucidate the influence of postnatal environmental enrichment on schizophrenia-like behavioral alterations induced by prenatal polyI:C immune stimulation at gestational day 9 in mice. Adult offspring were tested for amphetamine-induced locomotion, social interaction, and problem-solving behavior as well as expression of dopamine D1 and D2 receptors and associated molecules, microglia density and adult neurogenesis. Prenatal polyI:C treatment resulted in increased dopamine sensitivity and dopamine D2 receptor expression in adult offspring which was not reversed by environmental enrichment. Prenatal immune activation prevented the effects of environmental enrichment which increased exploratory behavior and microglia density in NaCl treated mice. Problem-solving behavior as well as the number of immature neurons was affected by neither prenatal immune stimulation nor postnatal environmental enrichment. The behavioral and neural alterations that persist into adulthood could not generally be modified by environmental enrichment. This might be due to early neurodevelopmental disturbances which could not be rescued or compensated for at a later developmental stage.

Effects of enriched environment on alterations in the prefrontal cortex GFAP- and S100B-immunopositive astrocytes and behavioral deficits in MK-801-treated rats

A plethora of studies have indicated that enriched environment (EE) paradigm provokes plastic and morphological changes in astrocytes with accompanying increments of their density and positively affects the behavior of rodents. We also previously documented that EE could be employed to preclude several behavioral abnormalities, mainly cognitive deficits, attributed to postnatal N-methyl-d-aspartate (NMDA) receptor antagonist (MK-801) treatment, as a rodent model of schizophrenia (SCH) aspects. Given this, the current study quantitatively investigated the number of cells, presumed to be astrocytes, expressing two astroglia-associated proteins (S100B and glial fibrillary acidic protein (GFAP)) by immunohistochemistry in the prefrontal cortex (PFC), along with anxiety and passive avoidance (PA) learning behaviors by utilizing elevated plus maze (EPM) and shuttle-box tests, in MK-801-treated male wistar rats submitted to EE and non-EE rats. Following a treatment regime of sub-chronic MK-801 (1.0mg/kg i.p. daily for five consecutive days from postnatal day (P) 6), S-100B-positive cells and anxiety level were markedly increased, while the GFAP-positive cells and PA learning were notably attenuated. The trend of diminished GFAP-immunopositive cells and elevated S100B-immunostained cells in the PFC was reversed in the SCH-like rats by exposure of animals to EE, commencing from birth up to the time of experiments on P28-85. Additionally, EE exhibited an ameliorating effect on the behavioral abnormalities evoked by MK-801. Overall, present findings support that improper astrocyte functioning and behavioral changes, reminiscent of the many facets of SCH, occur consequential to repetitive administration of MK-801 and that raising rat pups in an EE mitigates these alterations.

Enriched environment improves synaptic plasticity and cognitive deficiency in chronic cerebral hypoperfused rats

Recent studies have indicated that environmental enrichment (EE) increases the sensorial and social stimulations and leads to strengthened plastic changes in the brain. In models of chronic cerebral hypoperfusion, the ability of an EE to restore the cognition depends on hippocampal synaptic plasticity. The mechanisms for this effect have not, however, been adequately studied. Thus, the aim of the present study was to evaluate the neuroprotective effects and underlying mechanism of environmental enrichment by assessment of spatial memory tasks as well as parameters of synaptic plasticity in rats subjected to occlusion of the bilateral common carotid arteries (2-VO) model. Male Sprague-Dawley rats were used in this study. The model group was established by occlusion of the bilateral common carotid arteries. The animals were tested for learning, memory performance and synaptic plasticity using Morris water maze (MWM), 8-arm Radial Maze (RM), and field potential recording, respectively. The rats subjected to 2-VO in EE exhibited a significantly lower number of working errors and reference errors in RM. Moreover, the enriched environment recovered the memory performance of hypoperfused rats and decreased the swimming time to reach the platform in MWM. In addition, conditions of the environment did not have any effect on baseline synaptic transmission and presynaptic plasticity, but housing the animals in EE rescued the impairment of LTP induction induced by 2-VO. These results suggest that EE ameliorates the LTP and spatial memory impairment induced by 2-VO. Our data indicated that the LTP recovery by EE in the rat models of 2-VO is probably mediated by post-synaptic mechanisms.

Postnatal MK-801 treatment of female rats impairs acquisition of working memory, but not reference memory in an eight-arm radial maze; no beneficial effects of enriched environment

RATIONALE

Memory impairment has been documented in MK-801 (NMDA receptor antagonist) model of schizophrenia, but less is known on the rescue and/or differential effects of MK-801 on short- and long-term memories.

OBJECTIVES

We determined the effects of MK-801 treatment and/or enriched environment (EE) on acquisition of reference and working memory in developing rats.

METHODS

Female Wistar rats were injected with MK-801 (1 mg/kg) from postnatal days (P) 6-10. Task acquisition, working memory error (WME), and reference memory error (RME) were assessed in an eight-arm radial maze task. Behavioral performance of rats was also tested in an open field test before (P35-P40) and after (P65-P70) radial maze training to assess anxiety and locomotion. EE was applied from birth up to the end of experiments.

RESULTS

MK-801 treatment did not influence task acquisition in the radial maze; however, by the end of training, MK-801-treated rats made significantly more WME, but not RME, compared to control rats. Ratio of WME to total error was also significantly higher in MK-801 group. EE prevented MK-801-associated behaviors in the open field but did not exert beneficial effects on working memory deficit in the radial maze task. EE per se affected behavioral performance of rats only in the open field test.

CONCLUSIONS

Our results suggest that postnatal MK-801 treatment differentially affects working and reference memory in a young brain. Anxiety and hyperactivity associated with MK-801 are observed more severely in adulthood. Dissociation of the positive effects of EE may suggest selective modification of distinct pathways.

Sex-specific restoration of MK-801-induced sensorimotor gating deficit by environmental enrichment

Despite ample evidence of N-methyl-D-aspartate (NMDA) receptor dysfunction in schizophrenia, no study has addressed the effects of enriched environment (EE) on sensorimotor gating deficits induced by postnatal NMDA receptor blockade. We evaluated the effect of EE on sensorimotor gating (measured by prepulse inhibition, PPI), or on sensorimotor gating deficit induced by the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) in both sexes of Wistar rats. Rats were injected with MK-801 (1 mg/kg) on postnatal days (P) 6-10. EE was provided from birth up to the time of experiments on P28-30 or P58-60. PPI data were collected at three prepulse intensities and then averaged to yield global PPI. MK-801 treatment reduced PPI significantly in both sexes. While EE per se had no significant effect on PPI, it restored MK-801-induced PPI deficit only in male rats. An extended period of EE did not influence PPI deficit in female rats. Our results indicate that postnatal exposure to MK-801 may exert long-lasting effects on neuronal circuits underlying sensorimotor gating. Sex-specific modulation of such effects by EE suggests sexually dimorphic mechanisms are involved.